Presentation
Ulnar pain after a fall
Patient Data
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Palmar subluxation of the extensor carpi ulnaris (6th compartment), probably related to subsheath injury.
Intrasubstance longitudinal tear of the extensory carpi ulnaris and fluid distension of the synovial sheath in its distal third.
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Palmar subluxation of the extensor carpi ulnaris (ECU) tendon (red arrow) from its fibro-osseous tunnel (green arrow).
Case Discussion
The extensor carpi ulnaris muscle originates at the level of the humeral epicondyle and inserts at the base of the 5th metacarpal.
In the wrist, it is located in the 6th extensor compartment, being the only tendon that has an osteofibrous tunnel with its own subsheath, a thin layer of collagen fibers, that surrounds the last extensor compartment.
In normal circumstances, the ECU sub-sheath is able to neutralize the ECU dislocating force.
However, there must be a balance between the ability of the ECU to move and the role of the subsheath in preserving tendon stability.
ECU tendinopathy refers to painful dysfunctions secondary to an imbalance between the mobility of the tendon and the need of the subsheath to maintain it in the 6th compartment.
From there, two types of ECU tendinopathy emerge, the "constrained" ones where the tendon becomes inflamed due to being trapped in its own compartment and the "unconstrained" or "restrictive" ones, the latter present in our case, where, from trauma the subsheath is injured and promotes volar subluxation of the tendon.