Diagnosing ulnocarpal abutment syndrome

3 minute read

In this case study, radiographs and MRI help identify the cause of pain at the back of the wrist when gripping or performing a push-up.

A 68-year-old man presented with insidious onset longstanding dorsal ulnar-sided wrist pain.

This was exacerbated with loading the wrist, especially with pronation and gripping objects and in “push-up” positions. No distinct history of antecedent trauma was recalled. There was associated swelling and limitation of forearm and wrist movement.

On examination, there was reproduction of pain with dorsal and volar displacement of the ulna with the wrist in ulnar deviation, and palpable tenderness between the ulnar styloid process and flexor carpi ulnaris tendon. There was a positive supination lift test.

On radiographs, there is positive ulnar variance, and subchondral lucency of the proximal articular surface of the lunate on the ulnar side. (Ulnar variance refers to the relative lengths of the distal articular surfaces of the radius and ulna.)

On MRI, this is further delineated, with full-thickness cartilage loss of the proximal ulnar articular cartilage of the lunate, a full-thickness tear of the radial half of the triangular fibrocartilage (TFC) disc, and subchondral cystic change and oedema. The adjacent lunotriquetral ligament is intact.

This constellation of findings constitutes ulnocarpal abutment syndrome, which is a degenerative condition due to chronic impaction between the ulnar head and the TFC complex and ulnar carpus, and results in a continuum of pathologic changes as described.

Palmer designed a classification system for this syndrome based on the mechanism (traumatic vs degenerative) and involvement of anatomical structures, progressing from TFC disc wear and tear in low grade cases, to chondromalacia of the lunate and eventually lunotriquetral ligament tear in high grade cases. This classification system is helpful in determining the mechanism of injury and directing clinical management.

Conservative management primarily comprises activity modification, anti-inflammatory medication and supportive splints.

Surgical management can consist of surgical resection of the distal ulna to shorten it (if there is no TFC tear), or the head of the ulna can be burred down with the help of arthroscopic instrumentation (arthroscopic wafer procedure) in the case of TFC perforation.

Figure A – Frontal radiograph showing a prominent ulnar articular surface relative to the radius (positive ulnar variance).

Figure B – Coronal PD demonstrating cartilage wear in the lunate proximal ulnar-sided articular surface (red arrows) and a full thickness tear of the triangular fibrocartilage disc (blue arrow)

Figure C – Coronal T2 fat saturated image demonstrating subchondral marrow oedema in the lunate proximal ulnar-sided articular surface (red arrow) and a full thickness tear of the triangular fibrocartilage disc (blue arrow)

Dr Sebastian Fung is a musculoskeletal radiologist who undertook an MRI imaging fellowship in Hospital for Special Surgery in New York. He now works in Sydney at St Vincent’s Private Hospital and Mater Hospital.

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