Abstract
Pathologies of the extensor carpi ulnaris (ECU) tendon are often due to de Quervain's tenosynovitis of the first dorsal compartment among the wrist tendon pathologies. A common cause for tendinitis and tenosynovitis of the ECU tendon is its dislocation. ECU dislocation is unique among all wrist tendon injuries due to its typical location within a fibro-osseous tunnel bordered by a fibrous sheath, which is termed as the subsheath. The subsheath is the main anatomic structure keeping the ECU tendon within the tunnel. Subsheath tears can lead to a fixed or dynamic pattern of ECU dislocation. This injury is more often seen in tennis players and golfers than in water polo athletes, as there are overall fewer water polo athletes when compared to tennis players and golfers. In this article, we will discuss the mechanisms, clinical presentation, magnetic resonance imaging (MRI) findings, differential diagnoses, and management options for chronic subsheath tears.