Effect of Ulnar Head Offset on Distal Radioulnar Joint Stability

Abstract

Purpose A complete ulnar head replacement may be indicated in cases of distal radial ulnar joint (DRUJ) dysfunction to address bony pathology in lieu of using a constrained total DRUJ prosthesis. Complete ulnar head implants are simple, but they may be unstable if soft tissue tension is not adequately restored. We hypothesized that incorporating an increased offset in the complete ulnar head replacement would lead to increased tension on the distal oblique interosseous ligament, increased contact force at the DRUJ, and improved joint stability.Methods Using a specially designed jig, we measured instability by comparing displacement under load (stiffness) of the DRUJ in 10 cadaveric specimens under 4 different conditions: (1) intact, (2) native head after excision of the triangular fibrocartilage complex, (3) replacement of the ulnar head with a standard offset ulnar head, and (4) replacement of the ulnar head with an increased offset ulnar head. No soft tissue repair was done. We measured anteroposterior displacement under load with maximum translation of 10 mm or maximum loads of 50 N. We tested all specimens with the forearm positioned in neutral, supination, and pronation.Results Excising the triangular fibrocartilage complex decreased the average stiffness of the DRUJ to 46% of the intact state, creating a simulated state of DRUJ instability. Replacing the ulnar head with the standard offset head increased average stiffness to 54% of the intact state. Increasing the ulnar head offset with the simulated total ulnar head replacement increased average stiffness to 77% of the intact state.Conclusions An increased offset ulnar head replacement improves DRUJ stability compared with a standard anatomic offset ulnar head replacement.Clinical relevance Understanding DRUJ morphology and offset is important in the treatment of DRUJ arthritis and instability.

Measurement of bony anatomical parameters of the distal ulna based on healthy adult data: A cross-sectional study

“…In recent years, much emphasis has been placed on improving the function of the wrist joint. An increasing body of evidence suggests that treating the ulnar styloid process is very important to restore the function of the wrist joint (17)(18)(19)(20)(21)(22)(23)(24)(25)(26). It has been established that the ulnar styloid process is relatively small, irrespective of the measurement approach, with a length of only about 4.5-inche.…”