Clinical History: A 44 year old recreational tennis player complains of chronic, worsening ulnar sided wrist pain. (1a) Gradient echo coronal, (1b) T1-weighted axial, and (1c) STIR axial images of the wrist are provided. What are the findings? What is your diagnosis?
Severe extensor carpi ulnaris (ECU) tenosynovitis with partial tearing and mild palmar subluxation of the tendon. The ECU subsheath is diffusely torn and irregular.
Ulnar sided wrist pain is a common clinical complaint and indication for MR imaging.” MR is able to detect and diagnose numerous ulnar sided abnormalities that may account for patient symptoms.” A not uncommon site of injury is the sixth extensor compartment, home of the extensor carpi ulnaris (ECU).
The ECU originates as two heads which attach to the lateral epicondyle and the middle third of the posterior ulna. It has a single distal insertion upon the posterior aspect of the base of the fifth metacarpal. The ECU functions to extend and adduct the hand, and is important in the ability to ulnar deviate the hand.
A unique anatomical characteristic of the ECU is the fibro-osseous tunnel which stabilizes the tendon at the level of the distal ulna.1 This fibro-osseous tunnel is formed by the distal ulna and a 1.5 to 2cm in length band of connective tissue referred to as the ECU subsheath (5a, 6a). The subsheath lies deep to the extensor retinaculum, which itself does not attach to or stabilize the ECU tendon. The ECU, its subsheath, and the extensor retinaculum are readily seen using MRI (7a).
ECU Tenosynovitis and Tendinosis
Tenosynovitis and tendinosis of the ECU are not uncommon, with these abnormalities being a frequent early finding in patients with rheumatoid arthritis.2 In athletes, the ECU is the second most common site of wrist tendinopathy,3 typically associated with rowing, racquet sports, and golf. In such patients, chronic stress upon the tendon results in inflammation of its synovial lining, causing tenosynovitis.4 Over time, stress may also lead to tendon degeneration and altered collagen content, resulting in tendinosis with or without partial tears (8a).
ECU Subluxation and Dislocation
Subluxation or dislocation of the ECU tendon requires an injury to the ECU subsheath. Although repetitive stress likely precedes injuries to the ECU subsheath, most patients who experience subluxation or dislocation of the ECU recall a traumatic event, typically occurring during supination, ulnar deviation, and wrist flexion. These positions increase the angulation of the ECU tendon relative to the ulna and result in maximal force upon the ECU subsheath.6 The most commonly reported sporting activities resulting in ECU subluxation or dislocation are tennis and golf.
Three characteristic sites of injury have been reported in patients who experience ECU tendon dislocation and subsheath injuries.7 The subsheath may remain intact but be stripped at its palmar/ulnar attachment, forming a false pouch into which the ECU tendon can sublux or dislocate (10a,11a). Ulnar sided ruptures of the subsheath, likely the most common pattern of injury, usually result in dislocation followed by reduction in which the tendon returns to a location deep to the subsheath (12a, 13a,13b). With radial sided subsheath rupture (14a), the tendon is more likely to relocate in a manner that leaves it lying atop the ruptured subsheath (12a), preventing functional healing of the subsheath.
Patients who experience acute ECU subluxation or dislocation often describe a traumatic incident with immediate, searing pain. The sensation of tendon dislocation and an associated pop may accompany the injury. On clinical exam, findings include intense pain on passive supination, pain on palpation of the ECU tendon at the distal ulna, and localized swelling.5
If an acute ECU subluxation/dislocation is not appropriately treated, chronic ECU instability may result. In such cases, the ECU subsheath never heals, and the tendon may remain in an abnormally palmar location relative to its ulnar groove (P). Altered mechanics lead to chronic irritation, and thus many such patients experience persistent tenosynovitis. The chronically unstable tendon, if used repetitively, may even cause osseous erosion of the distal ulna.8
In rare cases, complete ECU tendon rupture may occur (16a,17a). In patients with tendon rupture, a characteristic cascade of events is often described.9,10 An initial acute luxation event is followed by lower grade but persistent pain, often with accompanying tenosynovitis. Local steroid injections may have provided temporary relief. Ultimately, increasing pain limits wrist activity, and subsequent imaging reveals the tendon rupture.
ECU tendinosis and tenosynovitis can often be managed conservatively. Splinting, rest, and non-steroidal anti-inflammatory medications are employed. Local steroid injection may also be of benefit, though it should be used with caution due to the increased risk of tendon degeneration and tearing. In patients who remain symptomatic despite conservative therapy, surgical release of the 6th extensor compartment yields excellent results.1 Release is accomplished via sectioning of the radial side of the ECU subsheath, followed by fixation of the extensor retinaculum over the region of release to prevent residual or recurrent ECU subluxation.
In patients with ECU subsheath tears and tendon instability, conservative therapy has also proven effective.5 The wrist is immobilized via casting in extension and radial deviation, which seats the tendon tightly within its ulnar groove. Activities that require movement of the elbow are limited. Depending on the severity of injury, immobilization is necessary for six weeks to three months.
Some authors, however, recommend surgical repair of ECU subsheath injuries, particularly when acute.6,11 Such an approach is particularly important in cases where the torn subsheath ends are widely separated, and is required if the tendon lies outside the torn subsheath. The most commonly utilized repair technique is a reconstruction of the subsheath using a strip of extensor retinaculum. The rare ECU ruptures are repaired via a graft from the palmaris longus.9,10 Associated injuries to the ECU subsheath are concurrently repaired. Following surgery, the wrist is casted in extension for a minimum of four weeks.
Ulnar sided wrist pain is both a frequent patient complaint and a common indication for MR imaging. Injuries to the extensor carpi ulnaris (ECU) are a well recognized but often poorly understood cause of such pain. Knowledge of the unique anatomy of the ECU and its subsheath must be gained in order to correctly diagnose patients with ECU tendon instability. The astute interpreter of MRI is able to accurately identify and characterize ECU tendon and subsheath abnormalities. Certain patterns of injury require operative repair, and thus MRI is a critical component of the treatment planning process.
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