Treatment of Severe Ulnar Instability of the MCP Joint Improves Function in LRTI Arthroplasty for Osteoarthritis of the Thumb CMC Joint.

Comorbidity in the metacarpophalangeal joint (MCPj) of the thumb, i.e., hyperextension or ulnar collateral instability, could affect the outcome of arthroplasty in the thumb carpometacarpal joint (CMCj).  In a retrospective study, we evaluated the effect of arthrodesis of the MCPj for thumbs with unstable MCPj and simultaneous ligament reconstruction tendon interposition (LRTI) arthroplasty for the CMCj in terms of strength, function, and patient satisfaction.  A total of 69 thumbs treated with a LRTI arthroplasty of the CMCj were included. In 14 of those cases, an arthrodesis of the MCPj was performed as well. In 12 thumbs, both procedures were done simultaneously; in one case MCPj arthrodesis followed LRTI arthroplasty, whereas one patient already had MCPj arthrodesis at time of LRTI arthroplasty. Those 14 thumbs were compared with the control group of 55 thumbs who had only undergone LRTI. At a mean follow-up of 4 to 5 years (mean 54 [10-124] months) postoperative assessments included range of motion (ROM) of the CMC, MCP, and interphalangeal (IP) joint of the thumb, as well as any instability of the MCPj. Pinch and grip strength were examined, also the visual analogue scale (VAS), patient satisfaction, QuickDASH, PRWE-Thumb, and the Kapandji's Opposition Score. Radiologically, proximalization of the first metacarpal bone was measured. Student's -test was used to determine significance,  < 0.05 was considered significant.  Additional arthrodesis of the MCPj provided no significant difference of function in thumbs that only had a hyperextension-instability. However, in thumbs with marked ulnar instability, stronger pinch-grip was obtained with arthrodesis, compared with only LRTI.  In patients with advanced painful thumb CMCj osteoarthritis, we recommend (simultaneous) arthrodesis of the MCPj, to allow a stable thumb grip if there is additional marked ulnar collateral ligament instability.  This is a Level III, retrospective comparative study.