In recent years, substantial improvement in transducer technology has led to a growing interest in the US evaluation of the hand and wrist (Bianchi et al. 1999, 2001; Chiou et al. 2001; Creteur and Peetrons 2000; Ferrara and Marcelis 1997; Fornage and Rifkin 1988; Lee 1998; Milbrat et al. 1990; Read et al. 1996; Teefey et al. 2000; Lee and Healy 2005). US transducers with frequencies ranging from 10 to 15 MHz allow accurate assessment of tendons, joints, nerves and vessels of the extremities without requiring stand-off pads. The association of standard radiographs with high-resolution US works well in the evaluation of wrist and hand disorders. Radiographs can recognize most bone and joint disorders and US can be used to assess a wide spectrum of pathologic conditions affecting soft-tissue structures.
From the anatomic point of view, the wrist is complex. For this reason, we will take a little time here to review the basic anatomy of the wrist with emphasis on the structures that can be assessed with US.
The wrist is composed of eight carpal bones arranged in two rows: proximal and distal. From lateral to medial, the proximal row includes the scaphoid, lunate, triquetrum and pisiform, whereas the distal row is formed by the trapezium, trapezoid, capitate and hamate. The arrangement of the carpal bones forms a ventral concavity which is transformed in an osteofibrous tunnel, the carpal tunnel, by the transverse carpal ligament. There are three joints in the wrist which, in normal conditions, do not communicate with one another: the distal radio-ulnar, radiocarpal and midcarpal joints (Fig. 1). Wrist movements are obtained by the concurrent action of the radiocarpal joint and midcarpal joint: wrist flexion and extension is produced half at the radiocarpal joint and half at the midcarpal joint, whereas radial and ulnar deviation of the wrist involves, at a higher extent (60%), the midcarpal joint.
The distal radio-ulnar joint articulates the rounded head of the ulna with the ulnar notch of the distal epiphysis of the radius and the triangular fibrocartilage. The distal radio-ulnar joint cavity is L-shaped and is separated from the radiocarpal joint by the triangular fibrocartilage. The capsule is formed by ventral and dorsal bands which extend from the surface of the radius to the ulna and includes a proximal pouch. The distal radio-ulnar joint is a pivotal type of articulation which allows pronation and supination movements of the hand.
The radiocarpal joint, which is also referred to as the proper “wrist joint”, is a condyloid type of synovial joint located between the distal end of the radius and the carpus. In the radiocarpal joint, the proximal concave articular surface is formed by the articular facet of the radius and the distal surface of the triangular fibrocartilage, a fibrocartilaginous structure filling the space between the ulnar head and the ulnar side of the carpus; the distal surface is composed of the convex surfaces of the scaphoid, lunate and triquetrum. On its ulnar side, the radiocarpal joint space may be in communication with the pisotriquetral joint, formed by the pisiform, a sesamoid bone found inside the flexor carpi ulnaris tendon, and the anterior facet of the triquetrum. The capsule of the radiocarpal joint is attached to the distal margins of the radius and ulna and to the proximal row of the carpal bones and is reinforced by extrinsic carpal ligaments.
The midcarpal (intercarpal) joint is located between the proximal and distal rows of carpal bones. Its capsule connects the proximal and distal rows and is reinforced by a high number of intrinsic ligaments. The midcarpal joint improves the range of movements of the radiocarpal joint and especially the grasp of the hand. More distally, the carpometacarpal joints articulate the bases of the metacarpals with the distal row of the carpal bones. These latter spaces normally communicate with the midcarpal joint.
The wrist ligaments can be classified as extrinsic and intrinsic. The extrinsic ligaments stabilize the wrist connecting the radius, the ulna and the bases of metacarpals with the carpal bones. Extrinsic ligaments are thicker and stronger on the volar side of the wrist. They are intracapsular and extrasynovial in location, being located between the capsule and the synovial layer of the joint. Overall, they have little clinical significance. Intrinsic (interosseous) ligaments connect and stabilize the carpal bones to one another, thus retaining the carpal bones (and especially those of the proximal carpal row) in the proper position during the complex movements of the hand. From a biomechanical point of view, the most relevant intrinsic ligaments of the wrist are the scapholunate ligament and the lunotriquetral ligament (Fig. 10.1). The scapholunate ligament has thick volar and dorsal components with a thinner portion in between them. Relative to the scapholunate ligament, the lunotriquetral ligament is smaller but has a similar shape. Intrinsic ligament tears may lead to instability of the adjacent joints and to irreversible degenerative changes resulting in limitation of range of movements, impaired function and pain.
The triangular fibrocartilage complex is formed by several soft-tissue structures located in the ulnocarpal space which increase stability to the ulnar side of the wrist and the distal radio-ulnar joint and absorb mechanical forces across the ulnar side of the wrist during axial loading. The complex includes the triangular fibrocartilage itself and other supporting structures which blend with it, such as the meniscus homologus, the ulnar collateral ligament, the volar and dorsal radio-ulnar ligament and the sheath of the extensor carpi ulnaris tendon. The triangular fibrocartilage is a biconcave disk positioned between the ulnar styloid and the radius. Its thickness is inversely proportional to the degree of ulnar variance.
Even using high-resolution transducers, most wrist ligaments are not visible with US and their proper evaluation requires MR imaging, MR arthrography or thin collimation spiral CT arthrography. Clinically relevant structures that are amenable to US examination are the scapholunate ligament and the triangular fibrocartilage complex.
The wrist is crossed by flexor and extensor tendons which course along its ventral and dorsal aspects respectively. Among them, nine flexor tendons and nine extensor tendons move toward the fingers without any attachment to the carpal bones; two primary wrist flexors and three wrist extensors insert onto the distal carpal row and the metacarpals; and one tendon, the palmaris longus tendon, attaches to the transverse carpal ligament and to the palmar aponeurosis.
The extensor tendons course over the dorsal aspect of the wrist. They run within series of adjacent osteofibrous tunnels delimited by depressions of the surface of radius and ulna and by the extensor retinaculum, a 2 cm wide thickening of the dorsal fascia attached to the radial styloid laterally and to the pisiform and triquetrum medially. From the deep surface of the retinaculum, vertical fibrous bands insert into the cortical bones, at both sides of the tendons, dividing the extensor tunnel into six compartments numbered from radial (I) to ulnar (VI). In each compartment, a single synovial sheath formed by visceral and parietal layers surrounds one or more tendons (Fig. 2). A variable amount of fatty tissue fills the space between the synovial sheath and the bone surface. From the biomechanical point of view, these tunnels give lateral stabilization and avoid bowstringing of the extensor tendons during wrist and finger movements. A bony protuberance, the Lister tubercle, is found between the second and third tunnels, acting as a useful landmark in the US identification of these compartments (Fig. 2).
The first compartment, the most radial, contains the abductor pollicis longus and extensor pollicis brevis tendons (Fig. 3). Medial to this, the second compartment houses the extensor carpi radialis longus and brevis which insert on the dorsal aspect of the base of the second and third metacarpals respectively. The third compartment contains the extensor pollicis longus. As already stated, this compartment is separated from the second one by the Lister tubercle of the radius (Fig. 3a). The fourth compartment is wide and encloses the tendons of the extensor digitorum for the second through the fifth fingers, and the tendon of the extensor indicis proprius, which is absent or rudimentary in approximately 40% of individuals (Fig. 4). The fifth compartment encloses the extensor digiti quinti proprius, whereas the sixth compartment, the most ulnar, includes the extensor carpi ulnaris tendon which courses along the dorsomedial aspect of the distal ulna to insert onto the base of the fifth metacarpal (Fig. 4). The tendons of the first compartment and the tendon of the extensor pollicis longus form the volar and dorsal boundaries of the anatomic snuff-box, a skin depression on the radial aspect of wrist crossed by the radial artery (Fig. 3a,b). To recall the exact name of the extensor tendons seems difficult but it is even harder to remember the exact position of them in each individual compartment, and especially in the first, second and fourth compartments. For an easier comprehension, one should keep in mind that: in the first compartment the extensor pollicis brevis tendon is more dorsal than the abductor pollicis longus; in the second compartment, the extensor carpi radialis brevis tendon is closer to the Lister tubercle than the extensor carpi radialis longus; in the fourth compartment, the extensor indicis proprius tendon is positioned on the ulnar side of the tendon for the index finger of the extensor digitorum; the tendon of the extensor pollicis longus crosses the tendons of the second compartment to reach the thumb (Fig. 3a,b). As a memo, the tendons from the first to the third compartment alternate as to longus and brevis as they proceed in an ulnar direction: abductor pollicis longus, extensor pollicis brevis, extensor carpi radialis longus, extensor carpi radialis brevis, extensor pollicis longus.
At the volar aspect of the wrist, nine flexor tendons enter the carpal tunnel to reach the fingers. There are four tendons from the flexor digitorum superficialis for the second through fifth fingers, four from the flexor digitorum profundus for the same fingers and the flexor pollicis longus tendon.
The flexor digitorum superficialis muscle gives rise to four tendons at the distal radius, just cranial to the proximal edge of the transverse carpal ligament. Then, these tendons pass within the carpal tunnel to diverge toward the fingers. During active fi nger movements, tendons of the fl exor digitorum superficialis can be palpated at the wrist between the prominences of the flexor carpi radialis and ulnaris tendons. The four tendons of the flexor digitorum profundus traverse the wrist just deep to the respective tendons of the flexor digitorum superficialis. In the carpal tunnel, the tendon of the index finger is separate whereas the remaining tendons to the third through fi fth fi ngers may become completely independent only in the palm. The lumbrical muscles arise in the palm from the tendons of the flexor digitorum profundus. The tendon of the fl exor pollicis longus lies deep to the fl exor carpi radialis in the distal forearm and passes on the radial side of the flexor digitorum tendons of the index finger in the carpal tunnel. On approaching the wrist, the tendons of the flexor digitorum superficialis and profundus become enveloped by a common synovial sheath. On transverse views, this sheath is “ε” shaped with a superficial extension which lies in front of the flexor digitorum superficialis, a middle extension lying between the flexor digitorum superficialis and profundus and a deep extension behind the flexor profundus. Just radial to the common flexor tendon sheath, the flexor pollicis longus tendon is enveloped by a separate sheath.
The primary flexors of the wrist, the flexor carpi radialis and the flexor carpi ulnaris, course outside the carpal tunnel and are readily palpable because they lie in a more superficial position than the flexor digitorum tendons (Fig. 5). The flexor carpi radialis tendon is a long flattened tendon which becomes oval in shape as it approaches the wrist. This tendon originates nearly midway between the elbow and wrist, is invested by an own synovial sheath and inserts on the palmar aspect of the base of the second metacarpal after coursing in a separate fibrous tunnel (vertical groove) made by an extension of the transverse carpal ligament. Its action allows flexion and concurrent radial deviation of the wrist. The flexor carpi ulnaris, the only tendon of the wrist not invested by a synovial sheath together with the palmaris longus tendon, is smaller in size and shorter relative to the flexor carpi radialis. This tendon courses on the ulnar side of the wrist housing the pisiform, which is considered a sesamoid bone in it, and inserts on the hook of the hamate (piso-hamate ligament) and on the fifth metacarpal (piso-metacarpal ligament). The flexor carpi ulnaris tendon is a landmark for the adjacent ulnar artery and nerve, both located just radial to them. Its action allows fl exion and concurrent ulnar deviation of the wrist, an essential action in some tasks such as using a screwdriver or a mallet.
The palmaris longus tendon is a long thin tendon which passes in the midline and superficial to the transverse carpal ligament (Fig. 5). Distally, it splits into diverging bundles which intermingle with the transverse carpal ligament and the palmar aponeurosis. It is absent in approximately 20% of individuals.
The wrist is crossed by the median nerve, the ulnar nerve and the superficial cutaneous branch of the radial nerve. In the wrist area, the ulnar nerve is accompanied by the ulnar artery and the median nerve gives off a sensory branch, the palmar cutaneous branch.
At the distal forearm, the median nerve courses in the fascial plane intervening between the flexor digitorum profundus and the flexor digitorum superficialis muscles. As the nerve approaches the wrist, it shifts radially and then moves superficially along the lateral margin of the flexor digitorum superficialis to align itself with the midline before entering the carpal tunnel (Fig. 6). Inside the tunnel, the median nerve runs superficial to the tendons of the flexor pollicis longus and the flexor digitorum superficialis for the second finger although its position may vary somewhat depending on wrist position. The nerve has an oval cross-section at the proximal tunnel and tends to become more flattened as it progresses distally through the tunnel (level of the hamate hook).
Throughout the carpal tunnel, the median nerve is covered by a strong fibrous band commonly referred to as the transverse carpal ligament or the flexor retinaculum (Fig. 6a,b). This is a localized thickening of the fascia that inserts on the tubercle of the scaphoid and trapezium (radial side) and on the pisiform and hook of the hamate (ulnar side) (Fig. 7). The median nerve provides sensory supply to the palmar aspect of the first three fingers and the radial half of the fourth, and motor supply for the muscles of the thenar eminence. Just proximal to the transverse carpal ligament, the median nerve sends a palmar cutaneous branch, which is a sensory nerve that supplies the radial half of the palm. This latter branch is very small and typically vulnerable to injury during carpal tunnel release.
In the distal forearm, the ulnar nerve lies on the radial side of the flexor carpi ulnaris and on the ulnar side of the ulnar artery. Here, it gives off two small branches: the palmar and dorsal cutaneous branches. More distally, the ulnar nerve pierces the deep fascia to continue in the wrist superficial to the transverse carpal ligament throughout the Guyon tunnel (Fig. 8). This small tunnel lies in a more superficial and medial location relative to the carpal tunnel. It is bounded by the pisiform medially (proximal tunnel), the hook of the hamate laterally (distal tunnel), the transverse carpal ligament (floor) and the palmar carpal ligament (roof). The Guyon tunnel contains the ulnar nerve (medial) and the ulnar artery (lateral) and veins embedded in fatty tissue. The ulnar nerve bifurcates within this tunnel into two terminal divisions – the superficial sensory branch and the deep motor branch – the latter supplying most of the intrinsic muscles of the hand, including the hypothenar muscles, the two medial lumbrical muscles, the adductor pollicis and the interosseous muscles. The ulnar nerve gives sensory supply to the medial aspect of the palm, the little finger and the medial half of the ring finger. Distal to the Guyon tunnel, the superficial branch has a straight course while the deep motor branch reflects across the palm to end at the first interosseous space (Fig. 8a).
At the distal radial aspect of the forearm, the superficial cutaneous branch of the radial nerve emerges between the tendons of the extensor carpi radialis longus and the brachioradialis to reach the subcutaneous tissue. At this point, the nerve is covered by a fascial band which connects the tendon and myotendinous junction of the brachioradialis muscle with the tendon of the extensor carpi radialis longus. More distally, the radial nerve pierces the fascia and overlies the anatomic snuff-box traversing the extensor tendons of the first compartment to provide sensory supply to the dorsum of the wrist, hand, thumb and proximal portion of the radial fingers.
The brachial artery has two terminal branches: the radial artery and the ulnar artery. At the distal forearm, the radial artery courses superficially over the ventral aspect of the distal radius where its pulse can readily be felt. Then, it curves dorsally over the radial aspect of the wrist, passes deep to the extensor tendons of the first compartment and crosses the floor of the anatomic snuff-box. The ulnar artery enters the wrist on the lateral side of the ulnar nerve and runs together with the nerve throughout the Guyon tunnel, superficial to the transverse carpal ligament. Somewhat similar to the nerve, the ulnar artery splits into a superficial palmar branch and a deep palmar branch.
Before US examination, the patient’s history should be carefully investigated to rule out any possible systemic articular disorder (rheumatoid arthritis and similar conditions), sporting or occupational activities possibly related to tendinitis and overuse syndromes, as well as local trauma (occult fractures, tendon ruptures, ligament sprains). At physical examination, the range of wrist movements (flexion-extension, ulnar-radial deviation, pronation-supination) can readily be assessed. An accurate location of the site of pain may be helpful in the case of tendinitis. In addition, movements that cause pain should also be tested. Recent standard radiographs, if any, should be reviewed for signs of joint and bones disease (i.e., osteoporosis, marginal erosions, focal bone lesions), abnormal position of bones (reflecting ligaments tears) and soft-tissue thickening and calcifications. When a space-occupying mass is encountered over the dorsal or palmar aspects of the wrist, intermittent variations in its size with time can suggest the diagnosis of a ganglion cyst. When the mass is linked to an adjacent tendon and follows it during movements, an intratendinous ganglion should be suspected.
In de Quervain disease, an inflammatory disorder affecting the first compartment of the extensor tendons, patients report tenderness and pain over the radial styloid. Typically, the wrist pain increases during grasping heavy objects. A useful diagnostic test is the Finkelstein test (Fig. 9). During this maneuver, the patient holds his or her thumb inside the clenched fist while the examiner tilts the patient’s hand in an ulnar direction to stretch the tendons of the first compartment. The Finkelstein test indicates de Quervain disease when it causes pain over the radial styloid that resemble the one described by the patient. Care should be taken, however, not to rely on this finding alone, because the Finkelstein test can be positive in normal subjects if the examiner applies excessive tension and in cases of rizarthrosis and radial styloiditis. As an alternative test, the examiner can maximally abduct the patient’s thumb while keeping the wrist in radial deviation. This latter maneuver is more specific because it pushes the tendons against the retinaculum and not toward the bone, thus recalling the same stress forces that generate symptoms in de Quervain disease. Both tests should be performed by the examiner because they help to direct the US examination to the first compartment.
Patients with carpal tunnel syndrome typically complain of night tingling and burning pain over the radial aspect of the hand and the first three fingers. The same symptoms can be felt during the day when a fixed position of the hand grasping an object is required, such as holding a heavy book or the telephone receiver. Because of the tingling, it is not unusual for patients to refer findings of carpal tunnel syndrome to a vascular disorder. Two clinical tests can be helpful to establish the diagnosis: the Tinel test and the Phalen test. The Tinel test is performed by tapping the volar aspect of the carpal tunnel with a reflex hammer (Fig. 10a), while, in the Phalen test, a full flexed wrist position is maintained for 1 min (Fig. 10b). Both tests are positive if they reproduce the patient’s symptoms. The examiner should be aware, however, that false negatives may occur in cases of chronic entrapment disease.
The patient is asked to sit comfortably in front of the examiner with both wrists and elbows resting on the examination table. Aged or traumatized patients may lie supine with the arm resting at the side of the body, although examination of the opposite side may become problematic in this position. For dynamic scanning of the extensor tendons, the hand is best placed on a gel tube with the fingers hanging over its edge to make fingers movements easier.
The routine US examination of the wrist begins with evaluation of its dorsal aspect, followed by the palmar one. Depending on the specific clinical presentation, US images can be obtained in different positions of the wrist (flexion and extension, radial and ulnar deviation, pronation and supination). Evaluation of gliding of the flexor and extensor tendons must always be performed during passive and active movements of the fingers.
Transverse US images are the best for detection and a proper identification of the extensor tendons. Assessment of the individual tendons is based on their anatomic position and behavior at dynamic examination (Lee anh Healy 2005). Detection of the extensor tendon for the third finger, for instance, is straightforward when transverse US scans are obtained during active flexion and extension of this finger while the others are maintained fixed by the examiner. On the other side, the extensor carpi radialis and the extensor carpi ulnaris are not affected by fingers movements and can be distinguished only on the basis of their anatomic position. US images are first obtained at the level of the distal epiphysis of the radius. The most useful landmark at this level is the Lister tubercle. This appears as a hyperechoic bony prominence over the dorsal surface of the radius. The tubercle separates the medial third compartment from the lateral second compartment. The extensor tendons appear as oval or rounded hyperechoic structures of different size. The extensor carpi radialis brevis and longus are the largest while the extensor pollicis longus and the extensor digiti quinti are the smallest. With high-resolution transducers, the extensor retinaculum appears as a thin transversely oriented fibrillar band which overlies each compartment. The septa of the retinaculum appear as thin hypoechoic bands at both sides of the tendons as a result of anisotropy. In most cases, the retinaculum of the fourth compartment is the thickest and more visible compared with the other compartments. In normal conditions, the synovial membrane enveloping the tendons and the sheath fluid cannot be depicted. We believe the best way to explore hand and wrist tendons is to assess each tendon or tendon group separately and to evaluate the different compartments in a sequential way. In clinical practice, one should first recognize the tendon and then follow it on short-axis planes its full length down to the distal insertion. Longitudinal US images may be useful to evaluate the fibrillar pattern of tendons and their dynamic motion in detail.
In the tunnel compartment, the abductor pollicis longus and extensor pollicis brevis tendons lie side by side over the lateral aspect of the radial styloid (Fig. 11). The floor of the tunnel is formed by a shallow groove of the radius. A small central crest within this groove may occasionally be seen. Two main anatomic variants may be encountered in the first compartment: (1) a vertical septum which splits the compartment into two distinct spaces; (2) accessory tendons that can be found in as many as 75% of cadaver dissections. The role of these anatomic variants in the pathogenesis of local tendinitis is discussed afterwards. The central septum can be appreciated with high-resolution US: it appears as a linear, vertically oriented hypoechoic band that divides the tunnel into a larger ventral and a smaller dorsal space (Fig. 12b-d). The anterior (ventral) tunnel houses the abductor pollicis longus whereas the posterior (dorsal) tunnel contains the extensor pollicis brevis. Accessory tendons are usually associated with the abductor pollicis longus (Fig. 12c,d). Their detection inside the first compartment may be difficult because of crowding of several tendons within a small tunnel. For this purpose, scanning in a more distal position, over the scaphoid, may be helpful to show the accessory slips that diverge to reach their different insertions. Although fluid within the tendon sheath is never seen in normal states, synovial sheath effusions may facilitate the detection of accessory tendons by increasing the contrast among them. More distally, the tendons of the first compartment pass lateral to the scaphoid and form the anterior edge of the anatomic snuff-box. The space between the scaphoid and these tendons is filled by loose connective tissue and houses the radial artery and veins (Fig. 13). Longitudinal US images over the radial styloid demonstrate these tendons resting on the radial cortex, whereas distal US images depict them at a certain distance from the scaphoid, somewhat forming a bridge between the radius and the base of the first metacarpal. The retinaculum is appreciated at the level of the radial styloid and its thickness can be measured on transverse scans (Fig. 11). Just superficial to the lateral aspect of the scaphoid, the radial artery can be assessed with gray-scale and Doppler imaging. In the subcutaneous tissue, the radial nerve is appreciated as a small fascicular structure encroaching the extensor tendons of the first compartment (Fig. 14). With high-resolution transducers, dynamic scanning can demonstrate the nerve snapping dorsally and ventrally over these tendons during pronation and supination movements.
At the distal radius, the extensor carpi radialis longus and the extensor carpi radialis brevis are seen coursing side by side to proceed toward the second compartment, while the muscles of the abductor pollicis longus and extensor pollicis brevis encroach superficial to them to reach the first compartment, the so-called “intersection” (Fig. 15). More distally, the extensor carpi radialis longus and brevis tendons diverge to reach the bases of the second and third metacarpals. Because of their greater size, these tendons can be easily evaluated and followed down to their distal insertions by means of short-axis planes. Longitudinal planes may be helpful to depict the internal echotexture of these tendons and are particularly useful to evaluate their distal insertion.
The extensor pollicis longus tendon is a thin tendon that has to be carefully evaluated because it is commonly involved by trauma or arthritis. Once detected at the medial side of the Lister tubercle, it must be followed on short-axis planes (Fig. 16). Because this tendon has an oblique course from medial (proximal) to lateral (distal), one should be aware that transverse scans must be oriented obliquely to maintain the scanning plane perpendicular to the long axis of the tendon. In fact, if the tendon is incorrectly imaged, it may exhibit a more pronounced oval shape and a larger cross-sectional profile. As the tendon progresses distally, it crosses the extensor carpi radialis brevis and the extensor carpi radialis longus. A careful scanning technique is required to depict the tendon intersection (Fig. 17). More distal images show the extensor pollicis brevis as it progressively joins the ulnar aspect of the extensor pollicis brevis which reaches its distal insertion at the base of the proximal phalanx. Long-axis US images on this small curvilinear tendon are difficult to obtain and, on the whole, not so useful.
The fourth and fifth compartments are routinely assessed together because of the close relation of the extensor digiti quinti with the extensor digitorum and the extensor indicis proprius. Transverse US images over the distal epiphysis of the radius show multiple slips of the extensor digitorum packed together inside the fourth compartment (Fig. 18). Because of their close apposition, static examination can hardly differentiate among these tendons. In order to identify them properly, selective dynamic scanning should be obtained while asking the patient to alternately flex and extend the respective finger while the examiner maintains the others fixed. On the ulnar side of the fourth compartment, careful US scanning shows the extensor digiti quinti coursing far from the bone, in a purely fibrous tunnel (Fig. 19). This tendon passes just superficial to the distal radio-ulnar joint. Flexion and extension movements of the little finger can enhance the detection of this small tendon. Dynamic US examination can also be useful to evaluate tendon gliding.
The sixth compartment is the easiest to be assessed with US as it contains only a large tendon, the extensor carpi ulnaris. Proximal US images demonstrate a shallow groove in the posteromedial aspect of the distal epiphysis of the ulnar, the extensor retinaculum appearing as a curvilinear anisotropic structure and the extensor carpi ulnaris tendon, located inside an osteofibrous tunnel (Fig. 20). More distally, the tendon can be seen overlying the ulnar styloid, which appears as a small rounded hyperechoic structure. After leaving the ulna, the extensor carpi ulnaris tendon rests on the dorsal surface of the hamate and then on the base of the fifth metacarpal (Fig. 20). Radial deviation of the wrist allows an optimal US depiction of the extensor carpi ulnaris in the longitudinal plane.
To evaluate the volar aspect of the wrist, the patient keeps his or her dorsal wrist facing the examination table. A standard US examination usually begins with transverse images obtained from proximal to distal.
The first anatomic level to be examined is over the pronator quadratus muscle. This muscle can be easily detected with US as a hypoechoic muscular belly lying over the volar aspect of the distal metaphyses of radius and ulna, deep to the flexor muscles and superficial to the distal radio-ulnar joint. As this muscle arises from the volar aspect of the radius to insert into the ulnar head, its fascicles are oriented transversely in contrast to the overlying flexor muscles which are oriented longitudinally (Fig. 21). This difference can be clearly appreciated with US by sweeping the probe from longitudinal to transverse planes and vice versa over the distal forearm. More distally, US demonstrates the styloid process of the ulna as a small hyperechoic rounded structure with posterior acoustic shadowing. The gap between the styloid and the radius is filled with the triangular fibrocartilage. This structure can be depicted by means of transverse and oblique coronal images (Fig. 22). On both scan planes, the triangular fibrocartilaginous complex appears as a triangular homogeneously hyperechoic area thicker than 2.5 mm (Chiou et al. 1998). At the pronator quadratus level, different tendons can be imaged with US: the flexor digitorum superficialis and flexor digitorum profundus, the flexor pollicis longus, the flexor carpi radialis and flexor carpi ulnaris (Figs. 21, 23, 24). At the radial side of the carpal tunnel, the flexor carpi radialis tendon appears as a hyperechoic oval structure overlying the hyperechoic cortex of the scaphoid. Longitudinal US images demonstrate this tendon as a straight fibrillar structure over the “S”-shaped ventral surface of the scaphoid (Fig. 24b). At the ulnar side of the tunnel, the superficial flexor carpi ulnaris tendon can also be seen (Fig. 24d). The location of the distal myotendinous junction of this tendon is variable (Grechenig et al. 2000). The flexor carpi ulnaris has a straight course and can be seen inserting at the proximal pole of the pisiform. In addition, its most superficial fibers may be disclosed as they overlie the pisiform and continue down to reach the pisohamate ligament. Compared with the flexor carpi radialis, the tendon of the flexor carpi ulnaris has a smaller cross-sectional profile. On gray-scale US images, the ulnar and radial arteries are readily visible because of their pulsatility. The main landmark for the radial artery is the lateral aspect of the flexor carpi radialis while the ulnar artery passes medial to the flexor carpi ulnaris (Fig. 23). More distally, the radial artery moves in a lateral position within the subcutaneous tissue, between the skin and the superficial aspect of the pronator quadratus (Fig. 24a). As it approaches the distal radius, this artery deepens to pass on the dorsal aspect of the wrist, within the anatomic snuff-box. Its palmar branch can be imaged in the subcutaneous tissue as a small hypoechoic pulsatile structure. Variations in size of the palmar branch are common and this vessel may also appear as large as the radial artery. The ulnar artery can be found in a more medial location. Anatomic variations in the number of wrist arteries can be found. The presence of a median artery of the forearm, close to the median nerve, can be readily assessed with US. When evaluating wrist vessels, care should be taken not to apply excessive pressure with the transducer on the artery to avoid its collapse and non-visualization.
Proximal to the carpal and Guyon tunnels, the median and ulnar nerves are recognized based on their peculiar fascicular echotexture. Approaching the wrist, the median nerve becomes more superficial and lateral and then runs toward midline and in a deeper position to enter the carpal tunnel (Jamadar et al. 2001). The palmar cutaneous branch of the median nerve arises from its palmar-radial quadrant approximately 5 cm cranial to the proximal wrist crease (Taleisnik 1973). It remains bound at the main nerve trunk to leave it after approximately 2 cm (Fig. 25). After piercing the antebrachial fascia or the transverse carpal ligament and entering the palm, the palmar cutaneous branch of the median nerve supplies the skin of the thenar and midpalmar areas. Awareness of the palmar cutaneous branch is important from the surgical point of vies to avoid inadvertent resection during release of the transverse carpal ligament performed with a too radial approach. Injury of this branch is followed by postoperative sensory disturbances. On short axis planes high-resolution US transducers can image this small nerve division. The ulnar nerve is found at the medial aspect of the distal forearm between the tendon of the flexor carpi ulnaris and the ulnar artery. Because of its close relationship with the ulnar artery, the ulnar nerve can be easily identified by detecting the pulsatility or the presence of color flow signals in the adjacent artery.
The most useful bony landmarks to identify the proximal carpal tunnel are the pisiform at its ulnar side and the scaphoid at its radial side. At US examination, these bones appear as round hyperechoic structures with posterior acoustic shadowing. Once these landmarks are demonstrated in a single image, the orientation of the probe should be adjusted to optimize the depiction of the soft tissues contained within the tunnel (Fig. 26). Tilting the probe back and forth may be helpful to distinguish the hypoechoic median nerve by the adjacent anisotropic tendons. Relative to the flexor carpi radialis, the flexor pollicis longus tendon runs in a deeper location, slightly closer to the midline. Oblique longitudinal US images can depict these tendons in the same plane. The proximal carpal tunnel is larger in size compared with the distal tunnel. In a comparative US-cadaveric study, US has proved to be accurate in evaluating the different diameters, the outline and the cross-sectional area of the carpal tunnel and the median nerve (Kamolz et al. 2001). The transverse carpal ligament appears as a thin slightly convex band of 1−1.5 mm thickness (Fig. 26). Its attachments to the pisiform and the scaphoid are readily detected with US. Because of its curvilinear shape, the anisotropic transverse carpal ligament may appear hypoechoic when the US beam is not perpendicular to it. This is particularly true at its attachments. Even with a careful scanning technique, high-resolution US is unable to depict the lateral division of the transverse carpal ligament which holds the flexor carpi radialis tendon. The nine flexor tendons (four from the flexor digitorum superficialis, four from the flexor digitorum profundus and the flexor pollicis longus) can be imaged inside the carpal tunnel as individual structures (Fig. 26). The identification of each of these tendons is easily accomplished based on their anatomic position (radial flexors rest on the radial side of the tunnel, ulnar flexors on the ulnar side) and by their action at dynamic US scanning. Compared with the round cross-sectional profile of the flexor digitorum tendons, the flexor pollicis longus is more oval in shape and its major axis is vertically oriented on transverse planes. At least in part, this may depend on the course of this tendon which diverges radially to reach the thumb. The median nerve courses superficial and parallel to the second and third flexor tendons and medial to the flexor pollicis longus tendon, just deep to the transverse carpal ligament (Fig. 26). Its cross-section is usually an ellipse, but its shape may change depending on wrist positions and varies among subjects (Kuo et al. 2001). In addition, even the size of the nerve seems to change relative to the wrist activity (MassyWestropp et al. 2001). During flexion of the fingers or fist clenching, transverse US images demonstrate passive shifting movements of the median nerve on the underlying gliding flexor tendons (Nakamichi and Takibana 1992).
Some anatomic variants of clinical relevance in the intracanal structures can be identified with US. The presence of anomalous muscles coursing within the carpal tunnel has been reported, including accessory fl exor muscles or the proximal extension of lumbrical muscles inserting into the flexor digitorum profundus tendons (Timins 1999). A bifid median nerve (presence of two paired nerves within the carpal tunnel) occurs when the main trunk splits in the distal forearm (Iannicelli et al. 2000, 2001; Propeck et al. 2000). Although the two components of the nerve can diverge proximally, they are most often arranged side by side within the tunnel (Fig. 27). The persistent median artery of the forearm is an accessory artery that arises from the ulnar artery at the proximal forearm and accompanies the median nerve along its course throughout the forearm and the carpal tunnel. It can be found in association with either a bifid median nerve or a normal nerve. In the first case, it lies in between the two nerve bundles; in the second, it runs on the ulnar side of the nerve (Figs. 28, 29). When associated to a bifid nerve, the artery and the nerve bundles may be enveloped by a common epineurium or may course freely, as separate structures. Anatomic studies have demonstrated the median artery in as many as 20% of cadaveric dissections (Rodriguez-Niedenfuhr et al. 1999). The presence of a median artery can be easily assessed with US and should be detailed in the report. In fact, the hand surgeon must be alerted to the presence of these anomalies because the nerve and the artery can be injured during arthroscopic release of the transverse carpal ligament.
The main bony landmarks of the distal carpal tunnel are the tubercle of the trapezium at its radial side and the hook of the hamate at its ulnar side. The trapezium is easily recognized because of its flat palmar surface, while the small curvilinear profile of the hamate hook is located closer to the midline with respect to the pisiform. Due to a more central location of the hamate hook, the distal tunnel is considerably smaller than the proximal one. In addition, the distal transverse carpal ligament is thicker at this level and has a straight appearance. As the tunnel becomes progressively narrower from proximal to distal, the median nerve tends to assume a more flattened appearance distally. Deep to the nerve, the flexor tendons are more difficult to differentiate from each other because they are closely apposed (Fig. 30). In addition, they lie in a deeper position, closely related to the volar capsule of the midcarpal joint. By sweeping the transducer on the radial side of the tunnel, the tendon of the flexor carpi radialis can be imaged inside a narrow groove under the tubercle of the trapezium. The flexor pollicis longus tendon is detected immediately medial to it. The overall size of the nerve can be subjectively estimated by comparing its crosssection with the underlying tendons. The fascicular echotexture of the median nerve is more evident proximally, at the entrance of the tunnel, where the nerve runs parallel to the skin and perpendicular to the US beam, than in the distal tunnel where the nerve has an oblique downward course. Tilting probe orientation or slight flexion of the wrist should be performed while evaluating the internal structure of the median nerve in the distal carpal tunnel. After exiting the distal edge of the transverse carpal ligament, the median nerve divides into two or three branches, the common palmar digital nerves, from which the digital nerves arise as terminal divisions for the opposite sides of the fingers (Fig. 31).
The Guyon tunnel is located in a medial and superficial position relative to the carpal tunnel. It is delimited by the dorsal aspect of the transverse carpal ligament and the superficial palmar carpal ligament on the radial side, and by the lateral aspect of the pisiform on the ulnar side. The transverse carpal ligament and the pisiform are easily detected with US. On the contrary, the superficial palmar carpal ligament is very thin and difficult to visualize. Once the curvilinear shape of the pisiform is found, care should be taken to identify the ulnar artery as a round, pulsatile hypoechoic structure. The ulnar nerve lies in between these two structures and can be better depicted by means of subtle tilting movements of the probe. It appears as a small structure of 2−2.5 mm in size, containing a few internal hypoechoic fascicles (Fig. 32a,b). The most commonly encountered anomalous muscle in the tunnel is the accessory abductor digiti minimi (Timins 1999). Distal to the pisiform, the distal Guyon tunnel can be imaged with very high-resolution transducers. At this level, the ulnar nerve can be seen dividing into two terminal branches: the superficial sensory branch continues to run close to the ulnar artery, whereas the deep motor branch courses alongside the medial surface of the hamate hook (Fig. 32c,d). Similarly, the ulnar artery splits into two branches, superficial and deep, each following the respective nerves bundles.
Tendinitis and tendinopathies of the dorsal wrist are common and account for a high percentage of consultations in hand surgery. They can be related to local causes, particularly overuse due to sport or occupational activities, or may be the result of systemic musculoskeletal disorders. Because the tendons of the dorsal wrist are invested by a synovial sheath, the term “tenosynovitis” is more correct to define most of these conditions. Typical sites of dorsal wrist tendinopathy include: the radial styloid for the extensor tendons of the first compartment (de Quervain disease); the level in which the extensor carpi radialis brevis and longus are crossed by the abductor pollicis longus and extensor pollicis brevis (intersection syndrome); the area around the Lister tubercle for the extensor pollicis longus tendon; the ulnar head region for the extensor carpi ulnaris (Fig. 33a) (Daenen et al. 2004). Since the extensor tendons tear more commonly in the hand than at wrist.
De Quervain disease is a typical example of overuse tenosynovitis of the wrist. This condition usually affects patients who perform repetitive movements of the thumb such as typists and piano players. New mothers are also commonly affected as a result of repeated extension and flexion of the wrist with abduction of the thumb against resistance, such as occur while holding the baby‘s head (Baby Wrist) (Anderson et al. 2004). Low grade chronic microtrauma at the level of the radial styloid can lead to localized thickening of the extensor retinaculum of the wrist, narrowing of the first compartment of the extensor tendons and subsequent impingement and inflammation of the extensor pollicis brevis and abductor pollicis longus tendons. Clinically, patients complain of tenderness and pain over the radial styloid exacerbated by wide movements of the thumb and forceful pinching of objects. As already described in Sect. 10.3.1, a useful diagnostic test, the Finkelstein test, is performed by applying passive ulnar deviation of the wrist with the thumb maximally flexed, a maneuver that aggravates the patient’s pain. Treatment of de Quervain disease relies on anti-inflammatory drugs and splinting. Resistant cases are treated with more invasive approaches such as local injections and surgical release of the retinaculum. A vertical septum splitting the first compartment seems to predispose to local tendon friction and is encountered more frequently in patients than in cadaver surveys (Bahm et al. 1995). Several authors have described the US appearance of de Quervain disease (Gooding 1988; Marini et al. 1994; Nagaoka et al. 2000; Trentanni et al. 1997; Giovagnorio et al. 1997). Both longitudinal and transverse US images are performed over the radial styloid. Although longitudinal planes are more valuable during dynamic scanning, transverse images give a better view of the retinaculum, internal septa and accessory tendons. The affected tendons are typically swollen and, as a whole, they have a more rounded cross-section under the retinaculum than in normal subjects (Figs. 34, 35). In acute phases, a synovial sheath effusion surrounding the tendons can be demonstrated caudal to the distal edge of the retinaculum, whereas in chronic longstanding disease the extensor tendons may appear hypoechoic or may have a heterogeneous echotexture. A thickened and hypoechoic extensor retinaculum should be accurately searched for at US because its demonstration can indicate the need for surgical decompression. Accessory vertical septa appear as thin vertical hypoechoic bands intervening between the tendons (Nagaoka et al. 2000). Demonstration of a vertical septum has clinical implications because it acts as a barrier to diffusion of injected steroids and requires opening of both tunnels at surgery (Leslie et al. 1990). In some cases, the inflammatory process may selectively involve one tendon when a septum is present (Fig. 36). In a postoperative setting, high-resolution US can identify complications, such as the volar subluxation of tendons due to an excessive section of the retinaculum (Fig. 37). In conclusion, although the clinical diagnosis of de Quervain tenosynovitis is not difficult, US can help to confirm it, detect whether a vertical septum is present, and assess postsurgical complications such as tendon instability.
The neuropathy affecting the superficial terminal branch of the radial nerve at the wrist is known as Wartenberg disease. This fairly common condition may be secondary to trauma or iatrogenic event, such as intravenous infusion, instability of the triangular fibrocartilage and nerve entrapment between the brachioradialis and the extensor carpi radialis longus tendons, most often occurring during activities that require forearm pronation with simultaneous flexion and ulnar deviation of the hand. The increased tension on the nerve causes ischemia, local inflammation and pain. Differentiation of Wartenberg neuropathy from de Quervain tenosynovitis or arthritis of the trapeziometacarpal joint is not clinically straightforward. In fact, these conditions may present with pain over the dorsoradial surface of the wrist and distal forearm radiating distally to the dorsum of the hand and thumb. High-resolution US examination is able to depict subtle abnormalities of the superficial cutaneous branch of the radial nerve following stretching or traumatic injures (Fig. 38). Therapy for Wartenberg disease depends on both local and causative factors. Corticosteroid injection at the site of tenderness along the nerve is the treatment of choice because it is effective with minimal distress to the patient. Since the superficial terminal branch of the nerve becomes entrapped at end-range pronation, this motion should be avoided.
Intersection syndrome is due to irritation of the two radial extensors of the wrist – the extensor carpi radialis longus and the extensor carpi radialis brevis – at the level at which they are crossed by the abductor pollicis longus and extensor pollicis brevis. This condition is usually secondary to occupational repetitive flexions and extensions of the wrist, such as occur in rowers and weightlifters. The clinical diagnosis is not straightforward because intersection syndrome may be easily confused with the more distal de Quervain disease. Wrist splints and local steroid injections are curative in most patients. Intersection syndrome appears at US as an ill-defined hypoechoic area between the two tendon groups, probably corresponding to local soft-tissue edema and tenosynovial fluid, with loss of the hyperechoic cleavage plane between them (Fig. 39). A true synovial bursa filled by fluid is a rare finding.
As already stated, the extensor pollicis longus tendon (third compartment of the extensor tendons) is a thin tendon that reflects over the medial aspect of the Lister tubercle before reaching the dorsum of the hand. Because of mechanical friction and its small size, the extensor pollicis longus is frequently affected by tenosynovitis that presents with local pain over the Lister tubercle and, less commonly, with local crepitus during thumb movements. This condition can be associated with previous fractures of the distal radius (Denman 1979) and leads to considerable tendon weakness, partial and complete tears if untreated. In extensor pollicis longus tenosynovitis, the synovial sheath effusion is typically found just proximal to the Lister tubercle and after the tendon has crossed the extensor carpi radialis longus (Fig. 40). Due to the restricted space under the fascia, the synovial sheath of this tendon may be distended with fluid in the area of the Lister tubercle and over the radial wrist extensors only when the amount of effusion is remarkable.
Extensor carpi ulnaris tenosynovitis is mostly secondary to instability of the retinaculum of the sixth compartment, as a result of mechanical friction of this tendon against the ulna. The patient typically complains of a localized pain over the dorsum of the ulna. Clinical findings are nonspecific and can mimic disorders of the distal radio-ulnar joint, especially when a snapping sensation is present. Although high-resolution US cannot accurately recognize distal radio-ulnar joint pathology, it can readily measure the tendon size, and is able to identify intrasubstance longitudinal splits related to recurrent tendon subluxation and to evaluate tendon sheath effusion and synovial hypertrophy (Figs. 41, 42). The relevance of a dynamic examination has to be emphasized in this setting.
The retinaculum most commonly torn at the wrist is that of the sixth osteofibrous tunnel which retains the extensor carpi ulnaris tendon in a correct position during rotation and flexion-extension movements of the forearm. This retinaculum tears as a result of acute trauma, chronic overuse and inflammatory changes in the extensor carpi ulnaris tendon sheath, such as in rheumatoid arthritis. Acute and chronic tears can be observed in sport injuries, including tennis practice, where the player performs a powerful pronation from a supinated position. This causes a sudden contraction of the extensor carpi ulnaris which stabilizes the ulnar head, and may lead to stripping of the retinaculum. Tear of the retinaculum related to rheumatoid arthritis will be discussed later, because this finding is closely related to the involvement of the distal radio-ulnar joint and the extensor carpi ulnaris tendon sheath. Regardless of the cause of retinaculum tear, the extensor carpi ulnaris tendon undergoes anterior (volar) dislocation. The instability of the extensor carpi ulnaris may result in either subluxation, when the flattened tendon moves over the medial aspect of the ulna, or intermittent dislocation, when there may be either spontaneous phases of dislocation and reduction, or permanent dislocations. Because of its high-resolution capabilities and dynamic scanning, US is the ideal imaging tool to confirm the instability of the extensor carpi ulnaris tendon (Fig. 43). Permanent dislocation of the extensor carpi ulnaris tendon is uncommon and can be identified by means of transverse planes obtained over the posteromedial aspect of the ulna. The diagnosis of intermittent dislocation is difficult if this possibility is not kept in mind by the examiner. To avoid false negative results, care should be taken not to limit the US examination to the static assessment of the tendon. On the contrary, transverse planes obtained during progressive pronation of the forearm can disclose the progressive displacement of the extensor carpi ulnaris tendon over the ulnar head.
Similar to the dorsal wrist, tendinopathies of the flexor tendons are commonly encountered, most often at the insertion of the flexor carpi radialis tendon and within the carpal tunnel for the flexor digitorum tendons (Daenen et al. 2004). In addition to tendinopathies, compression neuropathy of the median nerve at the carpal tunnel is the leading pathology of the wrist as regards prevalence of disease and clinical relevance. The entrapment of the ulnar nerve at the Guyon tunnel is rare and, in many cases, secondary to other disorders.
At the proximal wrist, the flexor carpi radialis tendon is held inside a splitting of the transverse carpal ligament bounded posteriorly by the scapho-trapezium-trapezoid joint. More distally, the tendon passes below the tubercle of the trapezium to become deep and insert onto the base of the second metacarpal. Although flexor carpi radialis tenosynovitis was only recently described (Fitton et al. 1968; Parellada et al. 2006), this condition is not widely recognized. Middle-aged women are most frequently affected. They report pain over the radial aspect of the volar wrist and a local lump, often misinterpreted as a volar ganglion. As an additional finding, tingling on the skin of the thenar eminence can be observed due to the close relationship of this tendon with the palmar branch of the median nerve ( Kerboull and Le viet 1995). Pathogenesis includes friction inside the carpal tunnel where the tendon curves to reach its posterior insertion and osteoarthritis of the first carpometacarpal joint and scapho-trapezium joint, which are considered the leading causes (Le Viet 1995). In this latter circumstance, tendon inflammation is secondary to the presence of volar osteophytes that cause impingement over the posterior aspect of the tendon during flexion and extension movements of the wrist. Surgery is only indicated if conservative treatment fails. In most cases, US examination is requested to rule out a volar ganglion because of a local swelling. The main US signs include a swollen and irregularly hypoechoic tendon (Fig. 44). A synovial effusion can often be found within the tendon sheath as an expression of tenosynovitis (Fig. 45). In some cases, longitudinal fissures can be encountered, especially arising from the deep surface of the tendon.
With the exception of the palmaris longus, the flexor carpi ulnaris is the only wrist tendon without a synovial sheath because of its straight course from the forearm to the distal insertion into the pisiform. The term “tendinopathy” is the most appropriate to describe this condition, because fluid cannot be demonstrated surrounding the tendon even in acute clinical settings. The most common disorder affecting the flexor carpi ulnaris tendon is calcifying tendinitis. This disorder predominantly affects young to middle-aged women, presenting with pain located just proximal to the pisiform. In general, the onset of pain is acute and physical examination shows a tender pisiform covered by inflamed warm skin. Symptoms are related to the rupture of intratendinous calcified deposits into the surrounding tissues with secondary acute inflammation. Therapy includes anti-inflammatory drugs, ice and immobilization. In cases of severe refractory pain, a brief (1−3 days) course of intramuscular steroids can be indicated. The diagnosis of flexor carpi ulnaris tendinopathy is based on clinical and radiological findings. Standard radiographs obtained in anteroposterior and lateral views can be negative, small calcifications being easily masked by the pisiform. If the diagnosis is suspected, an additional oblique view should be obtained to clearly show the broken calcified deposits (Fig. 46a). High-resolution US can easily image the flexor carpi ulnaris tendon due to its straight superficial course. Calcified deposits usually appear as spotty hyperechoic foci located between the tendon and the pisiform. Color and power Doppler imaging can demonstrate signs of hyperemia in cases of acute inflammation (Fig. 46b). The pisiform itself can exhibit small cortical erosions related to local inflammation (Fig. 46c). If US is the first imaging modality and calcifying tendinitis of the flexor carpi ulnaris is suspected, radiographs should always be performed to confirm the diagnosis.
Carpal tunnel syndrome is the most common entrapment syndrome of the upper limb with an estimated prevalence of approximately 125×106 new cases per year. This syndrome arises from compression of the median nerve at the wrist. Predisposing factors may be related to anatomic variants (i.e., narrow tunnel, presence of the median artery, abnormal and accessory tendons and muscles), susceptibility of the nerve to pressure (i.e., diabetes, systemic neuropathies), systemic and endocrine disorders (i.e., pregnancy, hypothyroidism, amyloidosis) and space-occupying lesions within the tunnel. Clinically, the patient, usually a late middle-aged woman, relates a history of tingling, numbness and burning pain localized in the thumb, index, middle finger and radial half of the ring finger, typically exacerbated by prolonged strenuous manual work. The dominant arm is more commonly affected. Night pain (brachialgia paresthetica nocturna) is the usual symptom that, at least in part, can be explained by local edema and prolonged wrist flexion during sleeping. In general, symptoms resolve after repeated hand movements. In early carpal tunnel syndrome, gross morphologic abnormalities of the median nerve do not occur. Later on, the nerve becomes swollen and exhibits changes in shape and histology with progressive demyelinization and fibrosclerosis. In chronic longstanding disease, permanent sensory and motor deficit in the territory of innervation of the median nerve can arise. Wasting of hand muscles is best appreciated at the volar aspect of the thenar eminence, causing a typical deformity of the hand, commonly referred to as “ape hand” (Fig. 47). Depending on the severity of symptoms and presence of atrophic changes in the muscles of the thenar eminence, treatment includes night splinting, intracanal steroid injections and surgical resection of the transverse carpal ligament.
An early diagnosis is essential to prevent permanent muscle damage and functional sequelae. In general, it relies on clinical and electrodiagnostic findings and, at least in typical cases, does not require an imaging study. However, the progressive refinement of US transducers has enhanced the ability to depict the median nerve in the carpal tunnel and high-resolution US is currently considered a low-cost, rapid and accurate modality to assess nerve compression in both static and dynamic states (Chen et al. 1997). The main US findings in carpal tunnel syndrome include changes in shape and echotexture of the median nerve and abnormalities in the transverse carpal ligament and the soft-tissue structures within the tunnel. Although the median nerve exhibits discrete morphologic abnormalities in many patients with carpal tunnel syndrome, some cases with early onset of symptoms do not show any detectable change at US examination. Accordingly, the examiner should be aware that a normal nerve does not exclude the diagnosis of median neuropathy. When abnormalities are present, the compressed nerve appears swollen at the proximal tunnel and flattened at the distal tunnel regardless of the cause of compression (Buchberger et al. 1991, 1992) (Figs. 48, 49). An abrupt nerve caliber change at the entrance of the carpal tunnel, commonly referred to as the “notch sign”, is typically appreciated (Lee et al. 1999). During scanning, this finding increases the diagnostic confidence of the examiner. In some cases, the notch sign may occur at a distal site, where the nerve passes below the distal edge of the retinaculum to exit the carpal tunnel (inverted notch sign). In this instance, the nerve and its divisional branches are swollen in the palm and flattened at the distal tunnel level (Fig. 50), whereas no shape change is usually appreciated at the distal radius and the proximal tunnel levels. An inverted notch sign indicates a distal compression and should be referred to the neurologist (to recommend functional tests with more sophisticated techniques, such as short segment and palmar stimulations, avoiding overly proximal routine electrophysiologic testing) and to the hand surgeon.
Since the nerve shape varies through the tunnel, some indexes have been introduced with US to better quantify abnormal findings in nerve morphology: among these, a nerve cross-sectional area ≥9 mm2 (Duncan et al. 1999) or ≥10 mm2 (Buchberger et al. 1992; Chen et al. 1997) calculated at the proximal carpal tunnel (scaphoid-pisiform level) by means of the ellipse formula [(maximum AP diameter) × (maximum LL diameter) × (π/4)] is reported to be the best diagnostic criterion for the diagnosis (Fig. 51a). Nevertheless, there is no consensus in the literature as to what size of the median nerve has to be considered abnormal. A nerve cross-sectional area ≥15 mm2 has also been proposed by other authors as the threshold value (Lee et al. 1999). These authors found a correlation between the nerve area and the severity of electrophysiologic findings and used 15 mm2 as the cut-off value to separate patients with severe disease in whom surgical decompression is indicated. In our experience, we found the point of maximum nerve swelling more commonly located behind the proximal edge of the transverse carpal ligament rather than at the proximal carpal tunnel level. Therefore, the greater difference in nerve cross-sectional area seems to be more reliably obtained by comparing the distal forearm level (pronator quadratus level) with the distal end of the radius. Using these landmarks, the cross-sectional area of the median nerve is approximately the same in normal states, whereas it may be greater than 2 in patients with carpal tunnel syndrome. In addition to proximal median nerve enlargement a distal flattening ratio >3, calculated at the distal tunnel by dividing the transverse diameter of the nerve by its anteroposterior diameter, has also been proposed as an additional finding of carpal tunnel syndrome (Buchberger et al. 1991, 1992). This latter finding, however, was not confirmed in later studies (Nakamichi and Tachibana 2000; Sarria et al. 2000) (Fig. 51b,c).
In addition to shape changes, high-resolution US can identify fine echotextural changes in the compressed median nerve, which becomes uniformly hypoechoic with loss of the fascicular pattern as a probable result of intraneural edema or fibrosis (Martinoli et al. 1996) (Figs. 48, 49). When evaluating the fascicular echotexture, care should be taken to place the nerve axis perpendicular to the US beam to avoid artifacts related to the oblique course of the fascicles. In addition, color and power Doppler imaging can show hyperemic blood flow in the longitudinal perineural plexus and within intraneural branches, related to disturbances in the intraneural microvasculature as well as to the inflammatory process (Martinoli et al. 2000). Reduced transverse sliding of the nerve beneath the retinaculum during flexion and extension of the index finger may also be seen, but this latter sign is too subjective and hard to quantify (Chen et al. 1997; Nakamichi and Tachibana 1995).
In carpal tunnel disease, the increased intracanal pressure may often lead to an increased convexity of the transverse carpal ligament that is normally straight or slightly convex. The bulging of the ligament can be appreciated with US and is measured at the distal tunnel (hamate-trapezium level) (Fig. 52). Once the tubercle of the trapezium and the hook of the hamate are identified, a line is drawn tangential to them. Then, the distance between this line and the most anterior portion of the transverse carpal ligament is calculated: a distance 4 mm reflects an excessive anterior bulging and can be considered an ancillary pathologic sign (Buchberger et al. 1991, 1992).
Besides assessing the median nerve and the transverse carpal ligament, extrinsic causes for nerve entrapment can also be identified with US. Most patients with carpal tunnel syndrome are affected by tenosynovitis of flexor tendons (Fig. 53). This condition may be secondary to a variety of causes and can be identified with US based on the presence of hypoechoic halos surrounding the flexor tendons due to fluid effusion and thickened synovium. In general, the synovial sheath effusion facilitates visualization and differentiation of the individual flexor tendons within the carpal tunnel. Dynamic scanning in transverse planes obtained during repetitive flexion and extension movements of the fingers may aid the differentiation between tendons and echogenic synovium. To avoid false negative results, scanning should be extended at more proximal and distal levels relative to the carpal tunnel because most synovial fluid may accumulate outside the tunnel where there is least resistance to sheath distension (Fig. 54). Comparison with the opposite uninvolved wrist may also be useful in the case of subtle findings.
A variety of space-occupying lesions can be encountered within the carpal tunnel. Ganglion cysts appear as lobulated anechoic masses with well-defined margins (Fig. 55). They usually arise in the deep portion of the tunnel from the wrist joints and dislocate both median nerve and flexor tendons against the transverse carpal ligament. Amyloidosis can be a complication of longstanding renal disease (Ikegaya et al. 1995; Lanteri et al. 1997; Takahashi et al. 2002). At US, it appears as an ill-defined solid hypoechoic mass arising over the radiocarpal and midcarpal joints that dislocates the intracanal structures (Fig. 56). Accessory muscles can also be found inside the carpal tunnel. They are related to either the proximal insertion of a lumbrical muscle, the distal insertion of a belly of the flexor digitorum muscles or are real accessory muscles. In all cases, anomalous muscles appear at US as hypoechoic masses with internal elongated hyperechoic lines reflecting muscular septa. Anomalous bone projecting inside the tunnel, such as an exuberant callus or a displaced lunate, appear as bright hyperechoic structures with posterior acoustic shadowing. A persistent median artery can occasionally be associated with carpal tunnel syndrome. In some patients, symptoms may arise suddenly as a result of acute thrombosis of this artery, a condition that requires thrombolitic treatment more than surgical excision (Fig. 57). US and color Doppler techniques make the diagnosis by showing lack of pulsatility and absence of internal flow in the occluded artery (Fumiere et al. 2002). Other masses that can cause carpal tunnel syndrome include lipomas and pigmented villonodular synovitis.
The conservative treatment of carpal tunnel syndrome includes wrist splints during sleep, nonsteroidal anti-inflammatory drugs and local corticosteroid injections adjacent to the tunnel. If such treatment fails or progressive sensory loss and muscle weakness and atrophy become apparent, surgical decompression of the transverse carpal ligament is recommended. Surgery may be performed with an open or endoscopic technique by dividing the retinaculum in proximity to its ulnar insertion on the hook of the hamate to avoid incidental damage to the branches of the median and ulnar nerves. After surgical release of the retinaculum, the appearance and mobility of the median nerve may improve and the cleft in the transverse carpal ligament can be seen with US (Fig. 58). Typically, the median nerve lies in a more superficial position at the proximal carpal tunnel level and the resected bands of the transverse carpal ligament are disposed obliquely on each side of the nerve. High-resolution US can be used in patients with unrelieved or recurrent symptoms to rule on incomplete sectioning of the transverse carpal ligament (early complication) or scarring involving the nerve (late recurrences) (Chen et al. 1997). In the case of incomplete section of the ligament, the notch sign continues to be appreciated in the median nerve although at a more distal level than observed preoperatively (Fig. 59). On the other hand, postsurgical scarring tissue in the carpal tunnel appears as an irregular hypoechoic mass with ill-defined margins encasing the median nerve.
In conclusion, when carpal tunnel syndrome is suspected on clinical grounds based on the patient’s history and the physical examination, high-resolution US can be a useful means to: confirm the diagnosis by showing changes in nerve shape and echotexture; rule out anatomic variants, such as a bifid median nerve or the presence of a median artery of the forearm, which may contraindicate arthroscopic access; assess the cause of compression. Detection of a space-occupying mass within the carpal tunnel usually suggests an open surgical approach. When compared with electrodiagnostic studies, US has proved to be nearly equivalent in the diagnosis. It has been suggested as initial test of choice for patients suspected of having carpal tunnel syndrome (Wong et al. 2004).
Compared with carpal tunnel and cubital tunnel syndrome, ulnar neuropathy at the Guyon canal is rare. The clinical symptoms of Guyon tunnel syndrome may vary depending on the site of compression of the ulnar nerve. From a pathophysiologic point of view, the Guyon tunnel can be divided in three anatomic zones (Gross and Gelberman 1984). Zone I corresponds to the proximal portion of the tunnel (pisiform level) and houses the main trunk of the nerve with sensory and motor fibers. Zones II and III are located more distally (hamate level): zone II corresponds to the deep portion of the tunnel where the motor branch of the nerve is held; zone III is superficial and contains the sensitive branch of the ulnar nerve. Depending on the site of compression within these different zones, the patient may have either mixed symptoms or a purely motor or sensory syndrome. The leading cause for Guyon tunnel syndrome is represented by ganglion cysts (Elias et al. 2001), which account for approximately 30−40% of cases of this syndrome. These ganglia originate from either the hamate-triquetrum or the piso-triquetrum joints, to which they are usually connected through a tortuous pedicle, and expand inside the Guyon tunnel. These lesions are readily diagnosed by high-resolution US (Fig. 60). They typically appear as well-delineated anechoic masses free of internal flow signals. The relationship of the mass with the ulnar nerve and the ulnar artery is best appreciated on transverse US scans. Usually, the origin of the ganglion cannot be established with certainty because its pedicle is almost never well depicted with US. In the preoperative planning, additional modalities should be performed, such as MR imaging and CT arthrography after injection of contrast material into the radiocarpal and eventually midcarpal joint, to assess the origin and extension of the mass in detail. Among other cases of Guyon tunnel syndrome, injures to the ulnar artery causing thrombosis and pseudoaneurysm formation, and anomalous muscles within the tunnel, such as the accessory abductor digiti minimi, may also lead to ulnar nerve compression by squeezing the nerve.
In a traumatic setting, acute injuries to wrist nerves are usually the result of penetrating injuries. The diagnosis of these lesions is straightforward on physical examination and US may have a complementary role in obtaining further confirmation of the clinical diagnosis and accurately assessing the precise site of the nerve lesion. In complete tears, the severed nerve is interrupted by an irregular hypoechoic area intervening between the nerve stumps related to hematoma and, later on, to fibrosclerosis. Typically, local pressure obtained with the probe over the lesion site can elicit acute pain (US Tinel sign). The US appearance of partial tears may be different depending on the nerve size. In small nerves, such as the divisional branches of ulnar nerve and the radial nerve, partial tears appear as a fusiform nerve swelling with hypoechoic echotextural changes (fusiform neuroma) in the absence of defects in nerve continuity. In large nerves, such as the median and the ulnar nerve, partial tears are best depicted in transverse planes showing the complete interruption of some fascicles whereas other fascicles retain a normal appearance (Fig. 61). With very high-frequency probes, a careful US assessment on short-axis planes can establish the percentage of affected fascicles. In most cases, an estimate of the fascicular involvement, i.e., whether less or more than 50% of fascicles are affected, can reliably be made. The wrist area where the median and ulnar nerves are particularly exposed to penetrating injures is located proximal to the carpal tunnel, where these nerves course superficially, just under the skin. The examiner should keep in mind that the flexor carpi radialis tendon is often affected in traumatic injures to the median nerve. Similarly, if the ulnar nerve is injured, the flexor carpi ulnaris tendon and the ulnar artery are rarely spared. Then, a nerve lesion should be suspected if an open injury is followed by loss of tendon function. As a rule, the tendons of the middle and ring fingers lie more superficial than those of the index and little fingers and are, therefore, more likely to be involved by lacerations on the ventral wrist. In chronic nonoperated tears of the median and ulnar nerves, a hypertrophied neuroma usually develops at the level of nerve section, possibly causing a lump on the ventral wrist (Figs. 62, 63). Another typical site of nerve lesion by occupation-related extrinsic causes is the area of the hamate hook where the divisional branches of the ulnar nerve course in close apposition to the bone. Chronic external pressure caused by repetitive stress on the ulnar aspect of the volar wrist by crutches or repetitive use of tools during manual work or sporting activities, such as biking, may be the cause of a ulnar neuropathy involving the superficial or deep branch of the nerve at this site (Fig. 64). In these cases, a fusiform nerve thickening can be appreciated just over the hamate hook. Galeazzi fracture-dislocation may also lead to secondary ulnar neuropathy.
Because of their superficial location and close proximity to the carpal bones, the vessels of the hand and wrist are particularly predisposed to direct trauma. Microtrauma to the vessel wall may cause intimal thickening with fibrin deposits that may lead to thrombosis and formation of pseudoaneurysms. The ulnar artery and its branches are typically affected at the Guyon tunnel (Hammer syndrome). The involvement of the superficial branch is more common because this small artery can be pinched between the skin and the hamate hook as the result of repeated local trauma. This often occurs in manual workers and in some recreational activities, such as biking (de Faucal et al. 1991; Klein et al. 1991). Patients complain of a localized pain at the ulnar side of the palmar wrist as the consequence of ischemic changes in the ring and little fingers due to microembolisms and vasospasms. High-resolution US demonstrates an enlarged artery with absent or diminished pulsatility and thickening of the arterial wall. The clot filling the lumen appears as a hypoechoic structure. Focal pressure with the probe can be painful and does not affect vessel size. Color and power Doppler imaging can enhance diagnostic confi dence by showing no flow signals in the artery. Small collaterals can be demonstrated all around the thrombosed artery as a network of irregular vessels joining the two ends of the thrombus. Retrograde flow can be encountered in the arterial palmar arches in cases of occlusion of the radial or ulnar artery. As a result of a similar compression mechanism, the superficial branch of the radial artery can be severed against the tubercle of the trapezium (Fig. 65). Also, the radial artery may be damaged at operation for removal of a palmar ganglion which may encircle the vessel. Repetitive microtrauma to the ulnar artery can cause weakening of the vessel wall up to formation of pseudoaneurysms. The mass effect of the pseudoaneurysm and its stiffness may lead to ulnar nerve compression. The clinical diagnosis maybe difficult in these cases because the patient with an aneurysm of the ulnar artery can have a mixture of neurologic and vascular symptoms. US demonstrates the hypoechoic sac of the aneurysm in continuity with the artery. Color and power Doppler imaging can be useful to confirm residual internal flow and to assess collateral vessels.
US has proved to be an accurate means to detect and quantify effusions in the distal radio-ulnar, radiocarpal, midcarpal and carpometacarpal joints (Koski 1992). Because the thickness of para-articular tissues is lower in the dorsal wrist, a dorsal approach is usually more adequate to assess these joint spaces. Fluid distention of the distal radio-ulnar joint is best depicted on transverse US images obtained at a more proximal level than the joint line, where the capsule has a greater compliance to distension (Fig. 66). Longitudinal US images are rarely useful to investigate the distal radio-ulnar joint. On the other hand, these are the best planes to assess the dorsal recesses of the radiocarpal and midcarpal joints (Fig. 67). Effusions in the radiocarpal, midcarpal and carpometacarpal recesses are, in fact, well depicted on midsagittal US images. At these levels, transverse US images are most useful to distinguish between deep intra-articular fluid and superficial sheath effusions of the extensor tendons. Coronal US scans may also be useful to investigate the radiocarpal joint at the level of the radioscaphoid space during passive radial and ulnar deviation of the wrist.
Similar to other joints in the body, differentiation between effusion and synovial pannus may not be easy at wrist due to their similar hypoechoic echotexture. As a general rule, the pannus appears more echogenic and pressure applied on it with the probe causes only a partial collapse of the recess, whereas free fluid is easily squeezed away from the field-of-view of the US image. Owing to the superficial position of the wrist joints, color and power Doppler systems can be helpful for this purpose by revealing blood flow inside the synovial membrane. One should be aware that the hyperemia is dependent on the degree of inflammation and that a less active “fibrous” pannus may appear completely free of color flow signals.
A variety of arthritides can affect the wrist joints, the most important of which are rheumatoid arthritis and psoriatic arthritis. Rheumatoid arthritis, is characterized by bilateral and symmetric synovitis. The first manifestation of arthritis is serous synovitis with moderate hyperplasia of the synovial membrane and hyperemia of the para-articular structures. Later in the course, the synovial membrane becomes markedly thickened and hypervascular, leading to formation of synovial pannus which causes bone erosions and disintegration of the articular cartilages. The pannus leads to progressive damage of the joint capsule and ligaments and subsequent joint instability. The diagnosis of rheumatoid arthritis relies on clinical features, serologic tests (Waaler-Rose and Latex tests) and radiographic findings. However, serology can be negative in patients with overt disease (seronegative arthritides) and radiography may demonstrate only late changes when erosions are present. Because an early diagnosis is critical for establishing aggressive therapy and preventing destructive joint changes, additional imaging modalities, such as MR imaging, are used. MR imaging is an accurate means to evaluate the para-articular soft tissues, to detect intra articular effusion and synovial pannus and to show cartilaginous damage and bone erosion (Sugimoto et al. 2000). However, this modality is expensive and not always adequate to ensure follow-up of chronic disorder.
In recent years, increasing attention has been directed to the role of US in the assessment of rheumatoid arthritis of the wrist and hand (Koski 1992; Koski and Hermunen 2001; Lund et al. 1995; van Vugt et al. 1997, 1998; de Flaviis et al. 1988). US findings of arthritic joints depend on the stage and severity of the disease. At early stages, high-resolution US can detect the presence and location of intra-articular effusions in the recesses of the wrist joint, thus allowing differentiation between joint and para-articular involvement (Fig. 68). In advanced disease, high-resolution US shows widening of the joint cavity and synovial pannus appearing as a hypoechoic structure partially or completely filling the joint space. At color Doppler imaging, the hyperemic pattern of the synovium correlates well with the disease activity and can be used as a parameter to follow up the patients (Fig. 69). When necessary, synovial biopsy (van Vugt et al. 1997) and intra-articular injection of corticosteroid (Koski and Hermunen 2001) can be effectively guided with US in the appropriate joint space.
Loss of definition and thinning of the articular cartilages may reflect the chondrolytic process of arthritis. The examiner should keep in mind that US allows only a partial evaluation of the hyaline cartilages of the radiocarpal and midcarpal joints due to the vertical orientation of many joint surfaces relative to the probe. In addition, the articular cartilages of the distal radioulnar joint cannot be depicted with US. At certain sites, however, dynamic scanning can improve their demonstration. This is true for the dorsal cartilages of the radiocarpal and midcarpal joints, such as the dorsal cartilage of the lunate, while scanning with the hand flexed. Again, the scaphoid cartilage can be better depicted when coronal planes over the radial aspect of the wrist are obtained with ulnar deviation. In chronic arthritis, bone erosions appear as areas of focal cortical discontinuity and as oval or round well-defined defects of the cortex (Fig. 70). Erosions can be seen filled by pannus that, in active synovitis, can show hyperemic fl ow coming from the inner bone (Fig. 69a,b). The sites more commonly involved by erosive arthritis are the dorsal aspect of the posterior horn of the lunate and the ulnar styloid. At these levels, erosions may be the result of synovitis of the distal radio-ulnar and radiocarpal joint, as well as of the involvement of the extensor carpi ulnaris tendon. As the destructive process progresses and the erosions grow in size and become more numerous, the carpal bones become indistinct and difficult to differentiate from one another. In patients with chronic disease, subluxation of joints follows weakening and rupture of ligaments, tears of tendons with a para-articular course and disintegration of the articular surfaces of bones. Functional insufficiency of the triangular fibrocartilage, secondary to chronic radiocarpal and distal radio-ulnar joint synovitis, may lead to dorsal dislocation of the ulnar head (Fig. 71). This latter finding associated with erosions and irregularities of the bony contours and inflammation of the adjacent sheath of the extensor carpi ulnaris tendon can lead to dislocation and longitudinal splitting of the extensor carpi ulnaris tendon and possible tears of the extensor digitorum of the ring and little fingers, the so-called caput ulnae syndrome (Fig. 72). Final stages of wrist involvement by rheumatoid arthritis are characterized by ankylosis that appears as a continuous hyperechoic line at the surface of wrist bones reflecting bone fusion.
Once the diagnosis of rheumatoid arthritis is made, the examiner should also accurately evaluate the integrity of para-articular tendons, because in longstanding tenosynovitis the cytokine-mediated lytic action of the pannus and the presence of enzymes in the synovial fluid can lead to their secondary damage. When involved by the disease process, tendons become swollen and may exhibit a heterogeneous fibrillar structure because of chronic biochemical and mechanical damage (Fig. 73). Then, they may appear thinner (reflecting a partial tear) or completely interrupted and retracted (reflecting a complete tear) (Fig. 74). In patients with rheumatoid arthritis, the extensor tendons of the little and ring fingers most commonly rupture at wrist (Fig. 75). As stated before, this seems to be secondary to repetitive friction over the irregular bony surface of the dorsally displaced ulnar head. Early US detection of tendon involvement is critical because it can indicate the need for tenosynovectomy, which is effective to prevent further tendon damage and complete tears. When partial and complete tears cannot be differentiated based on clinical findings alone, dynamic US evaluation can be useful to give direct demonstration of the lack of tendon movements. In complete ruptures, high-resolution US has a value in accurately locating the proximal retracted end of the torn tendon (Fornage 1989) and in excluding any nerve compression, such as that of the posterior interosseous nerve at the elbow, which can possibly mimic tendon ruptures.
Another typical complication related to the inflammatory process in rheumatoid arthritis is tendon instability that occurs secondary to loosening or rupture of the retinacula. This condition affects the extensor carpi ulnaris tendon and derives from involvement of the distal radio-ulnar joint by the pannus with secondary tearing of the triangular fibrocartilage and upward displacement of the ulnar head, or by weakening of the tendon sheath. The ventral displacement of the extensor carpi ulnaris can be seen during supination or palmar flexion of the wrist and requires dynamic scanning for proper assessment. Longitudinal splitting can complicate the intermittent snapping of the tendon over the irregularly eroded cortex of the ulna.
The scapholunate ligament plays an essential role as a stabilizer of the proximal carpal row during wrist motion, maintaining the scaphoid in a correct position and preventing its palmar tilt. Ligament tears result in scapholunate diastasis, palmar flexion of the scaphoid, dorsal flexion of the lunate and proximal repositioning of the capitate. Longstanding ruptures lead to degenerative changes at the capitate-lunate and radio-scaphoid joints, the so-called SLAC wrist (Scapho-Lunate Advanced Collapse), a painful condition that greatly reduces the range of motion of the wrist. Some authors have reported the US appearance of the normal scapholunate ligament (Griffith et al. 2001) and the range of normal scapholunate intervals in different degrees of ulnar and radial deviation. Due to its anatomic position, only the dorsal and ventral components of this ligament can be examined by means of transverse dorsal and ventral imaging planes. In this study, the dorsal component was completely visible in 48% of cases, partially visible in 30%, barely visible in 8% and not detectable in 15%. The scapholunate ligament appears as a hyperechoic fibrillar structure bridging the hyperechoic cortex of the two bones (Jacobson et al. 2002). The mean thickness of its dorsal band is 1.1 mm and the mean interosseous distance is 4.2 mm. Because of its deep location, the thin ventral component of the ligament is barely visible. Considering the high percentage of poorly visualized dorsal ligaments, its non-visualization at US does not indicate injury. Although the measurement of the interosseous distance is hampered by technical reasons (unclear landmarks for caliper positioning), a clear increase in its size during scanning with ulnar deviation of the wrist should alert the examiner to suggest further imaging modalities to confirm a possible tear (Fig. 76). Complications of failed surgical repair of the scapholunate ligament can seldom be demonstrated with US.
The triangular fibrocartilage of the wrist can be depicted with US using a palmar approach with transverse and oblique sagittal images (Chiou et al. 1998). In these planes, it appears as a triangularly shaped homogeneous hyperechoic area of >2.5 mm (confidence level 95%) in thickness, somewhat similar to the knee menisci and the glenoid labrum. In arthrographically proven pathological cases, tears of the triangular fibrocartilage can be appreciated with US as either a focal thinning (<2.5 mm) or a localized hypoechoic cleft within it (Fig. 77). Some authors have reported a sensitivity of 68.4% and a specificity of 96.4% for the US diagnosis of triangular fibrocartilage tears (Chiou et al. 1998). In our own experience, we encountered difficulties in accurately assessing the thickness of the triangular fibrocartilage in both normal and pathologic states as well as in reliably assessing its tears.
In addition, US seems inadequate to differentiate traumatic and degenerative lesions, which can have therapeutic and legal implications. Although results in progress from some groups are encouraging in this field (Keogh at al. 2004), we believe that additional efforts should be made to establish the ultimate role of US in evaluating lesions of this structure.
Calcification of wrist ligaments can follow traumatic injuries or result from crystal pyrophosphate deposition disease. In this disorder, wrist calcifications can be found within the triangular fibrocartilage and within intrinsic and extrinsic wrist ligaments, such as the scapholunate and lunotriquetral ligaments. US is not considered the best modality to detect crystal depositions and a definite diagnosis of crystal pyrophosphate deposition disease basically relies on standard radiographs and analysis of the synovial fluid. Nevertheless, the examiner must be aware of these findings as they can be detected incidentally during a routine examination of the wrist (Fig. 78). The appearance of ligament calcifications is that of hyperechoic spots embedded within the involved structure. Once US has suggested the diagnosis and the finding is believed clinically useful, an anteroposterior radiograph should be obtained to confirm it.
It is undisputed that the diagnostic investigation of wrist fractures and dislocations relies on clinical findings and standard radiographs and not on US findings. Nevertheless, the anatomic complexity of the wrist area often means some wrist fractures and dislocations are unnoticed on standard radiographs. In this setting, high-resolution may have an ancillary role in detecting occult fractures, bony avulsions and dislocations during a conventional US examination of the wrist. For this reason, bone surfaces should be accurately analyzed during a routine US examination, because even small irregularities can suggest the correct diagnosis. The US appearance of traumatic lesions of wrist bones includes a step-off deformity or a focal interruption of the cortical continuity in fractures and a disruption of the normal relationship between two adjacent bones in dislocations. When the occurrence of a fracture is suspected at US examination, further imaging studies with additional radiographic views, CT and MR imaging must be obtained depending on the specific situation to confirm the diagnosis as well as to assess the number and position of the fragments in fractures or the relation of bony ends in dislocations.
The scaphoid is the most common site of occult fractures in the wrist area, with up to 20−25% of cases unnoticed at the initial evaluation ( Waizenegger et al. 1994). When the diagnosis is delayed, scaphoid fractures have high rates of complications such as pseudoarthrosis, avascular necrosis of the proximal pole of the bone and secondary radiocarpal osteoarthritis with chronic pain and impaired function. A variety of diagnostic modalities, such as additional radiographic views, bone scan, CT and MR imaging, have been advocated for early detection of scaphoid fractures. The choice between an additional radiograph obtained after 10 days and more expensive modalities depends on the specific clinical situation, equipment availability and economic factors. High-resolution US can evaluate the scaphoid cortex by means of longitudinal images obtained over its palmar and lateral aspects. With both lateral and palmar approaches, care should be taken to align the transducer to the long axis of the scaphoid. Longitudinal images over the lateral aspect of the bone demonstrate a small ridge at the middle third of the lateral face refl ecting the scaphoid tubercle. This tubercle separates the proximal articular facet from the distal nonarticular portion of the bone and should not be misinterpreted as a fracture (Fig. 79). Several studies have reported the main US findings in cases of scaphoid fracture (Hodgkinson et al. 1993; Herneth et al. 2001). Two scanning technique have been proposed. In the first, color Doppler imaging is used to measure the distance between the radial artery and the scaphoid cortex using a lateral approach ( Hodgkinson et al. 1993). The superficial displacement of the artery due to post-traumatic local edema is assessed in comparison with the unaffected side. A scaphoid index has also been introduced to reduce the variability in the normal scaphoid-radial artery distance. For threshold values 30%, a 100% sensitivity and 74% specificity were reported for this index. With progressive advancements in transducer technology, some authors also described the ability of US to detect scaphoid fractures based on detection of a focal interruption of the hyperechoic bony cortex (Herneth et al. 2001; Hauger et al. 2002) (Fig. 80). A meticulous scanning technique with transverse and longitudinal US scans over the ventral, lateral and dorsal aspects of the scaphoid in both neutral and ulnar deviation positions is required for this study. Based on cortical disruption as the only diagnostic key, US proved to have 100% sensitivity, 98% specificity and 98% accuracy for the depiction of fractures of the waist of the scaphoid (Hauger et al. 2002). As an additional feature, some authors interpreted an echogenic line parallel to the cortex as an expression of periosteal elevation (Herneth et al. 2001). We believe this latter sign cannot be reliably differentiated from the acoustic interface between fluid and cartilage. However, based on cortical discontinuity and/or periosteal elevation, these authors showed an 87% overall accuracy of US for depicting occult fractures compared with 73% for scaphoid radiographic views or clinical examination (Herneth et al. 2001). The use of US to assess the stability of the fracture ends by real-time dynamic examination has also been investigated (Dias et al. 1994).
Other carpal fractures occasionally recognized with US are trapezium fractures and hamate fractures after dorsal dislocation of the fourth and fifth metacarpals. Small avulsion fractures of the dorsal triquetrum may also occur as the result of wrist injuries in hyperflexion and hyperextension. These latter fractures are very difficult to detect on standard radiographs unless tangential views are obtained. High-resolution US identifies the avulsed bone as a small hyperechoic fragment surrounded by a hypoechoic halo due to perilesional inflammatory edema (Fig. 81). Local pain enhanced by pressure with the probe is confirmatory of the diagnosis. After osteosynthesis for wrist fractures, US can also recognize postsurgical complications related to the inappropriate positioning or displacement of orthopedic hardware. The conflict of screws and metallic plates with superficial soft tissues may be responsible for tendon impingement and tears. In such cases, US is a valuable tool to identify the severed structures and the hardware material as the cause of impingement (Figs. 82, 83).
The diagnosis of dislocation of carpal bones may be challenging on plain films. Dislocations affect mostly the lunate which, being free from tendon attachments, is prone to volar dislocation, a condition commonly referred to as perilunate dorsal dislocation of the wrist. Even if radiographic examination can recognize the displacement of the lunate, in some cases this condition goes unnoticed at the first examination and US can be required to assess the cause of edema and functional inability of the wrist. Longitudinal and transverse US images over the carpal tunnel reveal the volar displacement of the bone which puts on view its concave articular facet, not detectable in normal states as it articulates with the capitate (Fig. 84). Direct compression of the flexor tendons and the median nerve by the displaced lunate can be depicted with US as well.
Clinically, a variety of pathologic conditions can present as space-occupying lesions around the wrist (Garcia and Bianchi 2001; Seboun et al. 1989). Once the lesion is identifi ed at physical examination, US can be used to confi rm its presence, evaluate its margins and internal echotexture (solid vs cystic) and rule out possible anatomic variants mimicking disease. Although the actual nature of a wrist mass cannot always be established based on US fi ndings alone, there are instances in which a specifi c diagnosis can be made or at least may be strongly suspected. These instances include: ganglion cysts, neurogenic tumors, anomalous bone and accessory muscles.
Ganglia, the most common space-occupying lesions of the hand and wrist, are cystic masses, filled with viscous fluid and lacking a true synovial lining, that derive from degeneration of periarticular soft tissues (Steiner et al. 1996). They present clinically as tender or slight painful masses close to joint surfaces. Most patients presenting with ganglia are completely asymptomatic and reach medical attention because of cosmetic deformity. Although the operative resection of hand and wrist ganglia is usually thought easy to perform, a recent survey on the postsurgical outcome revealed postoperative pain, limitation of function and local recurrence in 28% of cases (Faithfull and Seeto 2000). US demonstrates wrist ganglia as well-defi ned anechoic structures with posterior acoustic enhancement, located close to a joint (Bianchi et al. 1994; Hoglund et al. 1994; Paivansalo and Jalovaara 1991; de Flaviis et al. 1987; Cardinal et al. 1994; Breidahl and Adler 1996; Osterwalder et al. 1997). Most ganglia occur on the dorsal aspect of the wrist (Fig. 85). Chronic old ganglia may present a more echogenic appearance due to thickening of their wall and internal septa (Fig. 86). The dorsal occult ganglion is a small, painful ganglion occurring at the dorsal aspect of the wrist that cannot be palpated at physical examination (Berghoff and Amadio 1993; Ho et al. 2001). In general, dorsal ganglia develops within the capsule, superficial to the scapholunate ligament (Fig. 85). They are often painful as a result of a simple pressure phenomenon exerted by the cyst within the capsule. In fact, large ganglia expanding outside the ligaments within the superficial soft-tissues of the dorsal wrist, and thus forming reservoirs which reduce the intracystic pressure, are less painful. Another possible explanation is the direct compression exerted by the emerging ganglion on the posterior interosseous nerve. In fact, the terminal branch of the posterior interosseous nerve travels on the ulnar side of the Lister tubercle between the extensor pollicis longus and the fourth compartment and then passes in close relationship with the scapholunate ligament. Ventral ganglia are usually located on the radial aspect of the wrist: they originate from the scaphotrapezium joint and typically expand toward the distal epiphysis of the radius where they may compress and displace the radial artery and the superficial sensory branch of the radial nerve (Urayama et al. 1998) (Fig. 87). These ganglia should be distinguished from pseudoaneurysms of the palmar branch of the radial artery, which most often occur over the tubercle of the scaphoid and arise from chronic microtrauma secondary to repetitive squeezing of the artery against the tubercle of the scaphoid. US can detect them as anechoic lesions in continuity with the adjacent artery, characterized by internal flow signals at color Doppler imaging. Intraosseous and subperiosteal ganglia in the wrist and hand are exceptional (Fig. 88).
In clinical practice, high-resolution US is a useful tool for the diagnosis of wrist ganglia, especially in cases of small-sized occult lesions (Cardinal et al. 1994; Blam et al. 1998). This technique allows an accurate evaluation of the size of the cyst and is able to clarify its location and relationship with adjacent vessels, tendons and nerves. In selected cases, US can effectively guide the aspiration of the ganglion and the local injection of steroids within its cavity (Breidahl and Adler 1996).
The differential diagnosis of dorsal ganglia includes the so-called carpal boss, a common abnormality which presents as a bony protuberance on the dorsal wrist intervening between the base of the second and third metacarpals, the capitate and the trapezoid. It either relates to an accessory ossifi cation center, commonly referred to as the os styloideum, or may result from osteoarthritic changes at the carpometacarpal joint (Timins 1999) (Figs. 89, 90). Although generally asymptomatic, the carpal boss can occasionally lead to pain and limitation of hand motion owing to osteoarthritis or slippage of the extensor tendons. Although US cannot be considered the modality of choice to detect this abnormality, this technique may be performed to rule out a dorsal ganglion. In these cases, the os styloideum appears as a small accessory bone located at the level of the carpometacarpal joint, whereas local osteophytes are shown as hyperechoic humps lying over the dorsal surfaces of wrist bones.
Peripheral nerve tumors of the hand and wrist, including schwannomas, neurofibromas and neural fibrolipomas, are uncommon. Most involve the median nerve and typically present as soft, slowly enlarging masses occurring in the volar aspect of the hand and wrist. Nerve tumors have a nonspecific appearance on US as they appear as oval hypoechoic solid masses with well-defined margins (Fig. 91). The feature of value in differentiating these tumors from other soft-tissue masses is demonstration of the continuity between the mass and the nerve of origin (Martinoli et al. 1996). This requires careful scanning technique because the normal nerve portions connected at the opposite ends of the tumor may be displaced from their natural course by the enlarging mass. The nerve immediately adjacent to the tumor may be thickened and have loss of anisotropy, thus producing a tapering appearance to the oval mass. Tumors of the median nerve at the wrist may cause bowing of the transverse carpal ligament, and carpal tunnel syndrome may be a late symptom.
A rare neurogenic mass with marked predilection for the median nerve at wrist is the neural fibrolipoma, a developmental anomaly which is also referred to as fibrolipomatous hamartoma or intraneural lipoma. Syndactyly or macrodactyly of the index and middle fingers (macrodystrophia lipomatosa) are associated with it in up to two thirds of patients. Fibrolipomatous hamartoma affects young subjects, often in early childhood, and presents clinically as a mobile soft-tissue swelling in the volar aspect of the wrist (Murphey et al. 1999) due to the striking enlargement of the median nerve by mature fibrofatty tissue that infi ltrates the interfascicular epineurium. US typically shows the fusiform enlargement of the nerve at the distal radius and within the carpal tunnel by large deposits of hyperechoic fat filling the epineurium and displacing normal or slightly enlarged hypoechoic fascicles (Chen et al. 1996) (Fig. 92).
Accessory muscles can be encountered at the wrist as merely incidental findings in asymptomatic subjects. In some cases, however, these muscles may cause clinical concern when they present as space-occupying masses or when their hypertrophy or strenuous activity causes compressive neuropathy. The typical US appearance of anomalous wrist muscles does not differfrom that of other muscles, including functional phases of contraction and relaxation. Familiarity with their location may help the examiner to make a correct diagnosis, thus avoiding confusion with other pathologic conditions. The most common anomalous muscles in the wrist are: the accessory abductor digiti minimi, the extensor digitorum brevis manus, the digastric flexor digitorum superfi cialis muscle of the index finger, and a proximal origin of the lumbrical muscles (Timins 1999).
The accessory abductor digiti minimi is the most common accessory muscle of the wrist, accounting for approximately 24% of normal individuals (Zeiss and Guilliam-Hadet 1996). This muscle originates from the palmar carpal ligament and the palmaris longus and inserts on the abductor digiti minimi and the medial aspect of the base of the fifth proximal phalanx (Patel et al. 2002) (Fig. 93). Although usually asymptomatic, it may cause ulnar neuropathy by squeezing the ulnar nerve against the pisohamate ligament during its contraction. A difference in muscle thickness between normal subjects (mean 1.7 mm) and symptomatic patients (4 mm) has been observed, indicating that the muscle size may be a factor influencing the function of the underlying nerve.
The extensor digitorum brevis manus occurs less frequently, involving 1−3% of individuals (Gama 1983). It arises from the distal radius and the distal radiocarpal ligament and inserts onto the index or the middle finger. The extensor digitorum brevis manus appears as a muscle belly located alongside the extensor tendon of the index finger and can be easily mistaken for either a dorsal ganglion or tenosynovitis of the extensor tendon of the index finger. US is able to identify the typical echotexture of a muscle and to depict muscle shape changes induced by voluntary contraction and relaxation (Fig. 94).
On the ventral wrist, an anomalous muscle belly of the flexor digitorum superficialis of the index finger may cause discomfort and symptoms related to carpal tunnel syndrome (Smith 1971). In these cases, the anomalous muscle can be seen entering the carpal tunnel during extension of the index finger. For a correct diagnosis, the examiner should best examine the wrist while keeping the fingers extended. Then, dynamic scanning during flexion and extension of the fingers can depict the muscle entering and exiting the tunnel (Fig. 95).
A proximal origin of the lumbrical muscles inside the carpal tunnel can be encountered in approximately 22% of subjects (Touborg-Jensen 1970). These muscles are pulled within the tunnel during flexion of the fingers and may be the cause of median neuropathy. Similar to the anomalous flexor digitorum superficialis of the index finger, dynamic scanning with flexion and extension of the fingers is essential for a proper diagnosis of anomalous lumbrical muscles.
Authors: Stefano Bianchi and Carlo Martinoli