Digital flexor tendon injuries in the wrist include lacerations and, less commonly, closed ruptures (Fig. 7) . The latter are usually associated with a variety of underlying chronic conditions that weaken the tendons, such as rheumatoid arthritis, osteoarthritis, scaphoid nonunion , Kienbock disease, hook of the hamate fractures, nonhealed distal radial fractures , and carpal dislocations. Sudden hyperextension of a flexed finger, most frequently seen in football or rugby players and less commonly following an electrical injury, can also lead to acute closed ruptures .
In a series by Drape and colleagues , MRI proved useful in displaying the zone of rupture, assessing the edges of the proximal and distal tendons, and accurately measuring the gap between the retracted tendon ends. Gap size is considered an important factor in treatment decision making, because a gap greater than 30 mm necessitates a tendon graft rather than a primary tendon repair . Assessment of integrity of the adjacent tendons before tendon graft may also be accomplished with MRI. MRI can also aid in locating the proximally retracted edge of the tendon, which in some cases may dislocate in between the adjacent tendons or even curl up in the palm [43,44].
In cases of volar carpal subluxation, rupture of the flexor pollicis longus tendon (FPL) may develop from chronic attrition against the volarly displaced scaphoid. Clinically, there is loss of active thumb flexion at the interphalangeal joint. The proximally displaced tendon edge may fold over itself at the entrance of the carpal tunnel, producing carpal tunnel symptoms. Surgical exploration of the volar aspect of the wrist should be performed to look for bony spicules that could have disrupted the FPL.
Tenosynovitis of the FCR is often traumatic in origin and may be secondary to either direct injury or chronic repetitive trauma. The tenosynovitis, however, may also develop insidiously, unrelated to trauma. Clinically, there is pain and crepitus over the FCR tendon in the region just proximal to the flexor creases of the wrist. MR findings include tendon sheath thickening with
associated hyperintensity on T2-weighted images (Fig. 8). Inflammatory changes of the scapho-trapezial joint have also been described . Because of its close proximity to the FCR, concomitant median nerve irritation may occur. MRI can be useful in approaching this entity, because the clinical diagnosis can be difficult, and it may be mistaken for scapho-trapezial joint disease, soft tissue ganglion, distal scaphoid fracture, distal radial fracture, and the Linburg syndrome .
De Quervain's disease is noted commonly in middle-aged women and may be bilateral in as many as 30% of patients. It is characterized by tendinopathy and stenosing tenosynovitis of the first extensor compartment, including the abductor pollicis longus and the extensor pollicis brevis tendons . The condition is most often idiopathic . A septum separating the first extensor compartment tendons has been described in as many as 70% of cases requiring surgical release for de Quervain's tenosynovitis . Other predisposing factors include inflammatory conditions such as rheumatoid arthritis, acute trauma, and chronic repetitive microtrauma from radial and ulnar deviation of the wrist
Typically, de Quervain's syndrome occurs at the level of the radial styloid or slightly proximal to it. The differential diagnosis includes infectious tenosyno-vitis of the first extensor compartment, first carpometacarpal joint osteoarthri-tis, FCR tenosynovitis, intersection syndrome, and isolated neuritis of the superficial radial nerve, also called ''Wartenberg's syndrome.'' MRI characteristics are fairly typical and include thickening and heterogeneity of the first compartment tendons and sheath, tenosynovial effusion and surrounding loss of fat planes due to soft tissue edema, and low-signal scar tissue (Fig. 9)
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