Ulnar-positive variance as a predictor of distal radioulnar joint ligament disruption

Previous cadaveric data show that disruption of the triangular fibrocartilage complex (TFCC) at the wrist allows 0.5 to 3.0 mm of proximal radius migration. Anatomic studies have documented the presence of superficial and deep fibers of both the palmar and the dorsal distal radioulnar joint (DRUJ) ligaments. The aim of this study was to determine the contribution of the superficial and deep fibers of the DRUJ ligaments to longitudinal forearm stability as measured by ulnar-positive variance.

Eight fresh-frozen cadaver specimens were included in this study. Each specimen was secured with external fixation clamps to a sequential loading frame with the elbow in 90 degrees of flexion and the forearm and wrist in neutral pronation supination, neutral ulnar-radial deviation, and neutral volar-dorsal angulation. The radial head was resected and a force gauge was applied to the proximal radius. The peripheral TFCC was identified through an incision between the fifth and sixth extensor compartments and the dorsal capsulotomy of the DRUJ capsule. After baseline measurement sequential transection of the superficial and deep fibers of the TFCC was performed. Before and after each step load application and removal were performed by attaching an 88.90-N weight to the end of a force gauge and via longitudinal traction on the proximal part of the radius, and ulnar variance was measured with wrist fluoroscopy.

Transection of the superficial TFCC fibers resulted in radius migration of 0.70 mm. This migration, however, was not significantly different from that observed at baseline. After both the superficial and deep TFCC fibers were transected the radius migrated proximately with load. This change of ulnar variance was significantly greater than that observed at baseline or after transection of only the superficial TFCC fibers.

Traumatic injury to the TFCC with radiographic evidence of ulnar-positive variance may be an indication of disruption of the deep TFCC fibers.