Radioscapholunate arthrodesis with excision of the distal scaphoid: comparison of contact characteristics to the intact wrist.

Purpose: To evaluate the midcarpal contact characteristics at the lunocapitate (LC) and scaphotrapezio-trapezoidal (STT) joints in 3 wrist conditions: intact, after simulating a radioscapholunate (RSL) arthrodesis, and after an RSL arthrodesis with distal scaphoid excision (DSE).

Methods: Eight fresh-frozen cadaveric specimens were tested using a custom jig with the wrist in neutral, 15° and 30° flexion and extension, 10° radial deviation, and 20° ulnar deviation. The RSL arthrodesis was performed using 2.4-mm distal radius plates with locking screws. Using a pressure sensor, contact force, average pressure, peak pressure, and contact area at the STT and LC joints were measured for 3 conditions: intact wrist, RSL arthrodesis, and RSL arthrodesis with DSE.

Results: Following RSL arthrodesis, average and peak pressure at the LC joint increased significantly compared to the intact wrist. In the STT joint, the average and peak contact pressure increased significantly compared to the intact wrist. Following DSE, average and peak pressure at the LC joint increased further compared to the RSL arthrodesis condition.

Conclusions: Our findings showed increased contact pressures in the STT and LC joint following RSL arthrodesis, which may explain the clinical findings of midcarpal arthritis. Also, although DSE may improve short-term range of motion and clinical incidence of midcarpal arthritis, our findings showed that this comes at a cost, as the remaining portions of the midcarpal joint are subject to higher forces and pressures following DSE.

Clinical Relevance: Radioscapholunate arthrodesis results in increased midcarpal contact pressures that may explain the clinical incidence of midcarpal arthritis. Excision of the distal scaphoid further increases contact pressures in the remaining midcarpal joint and may further increase the incidence of midcarpal arthritis. These alterations in contact characteristics of the midcarpal joint should be considered when excising the distal scaphoid for improved range of motion.