ABSTRACT
PURPOSE: Trapeziometacarpal (TM) arthrodesis may increase adduction motion of the thumb metacarpophalangeal (MCP) joint, causing radial collateral ligament laxity. Stability of the MCP joint is important to the long-term functional outcome after TM arthrodesis. This study assessed preoperative and postoperative radial collateral ligament laxity using dynamic radiographs to confirm whether laxity was exacerbated after surgery and examined whether there is a relationship between the fixation angle of arthrodesis and the degree of laxity. METHODS: Forty-four thumbs in 33 patients who underwent TM arthrodesis and were followed for at least 5 years were studied. Dynamic radiographs in radial adduction-abduction and palmar adduction-abduction were obtained. We defined the midpoint of arc of motion as the fixation angle of arthrodesis in the radial and palmar planes. We measured the intersection angle between longitudinal axis of the first metacarpal (M1) and that of thumb proximal phalanx (P1). P1M1 angle in a palmar adduction view of dynamic radiographs reflected radial collateral ligament laxity in palmar adduction (adduction P1M1 angle). We subtracted a preoperative adduction P1M1 angle from a postoperative adduction P1M1 angle and defined its value as an exacerbated adduction P1M1 angle. RESULTS: Adduction P1M1 angle increased from 9° ± 5° to 18° ± 10°. The median exacerbated adduction P1M1 angle was 7°. Ten thumbs (23%) developed ulnar subluxation of MCP joint in the palmar adduction view of dynamic radiographs. Among them, two thumbs developed osteoarthritis of MCP joint (5%). Fixation angle of the arthrodesis was a mean of 35° ± 7° and 32° ± 9° in the radial arc and palmar arc planes, respectively. There was a positive correlation between increasing adduction P1M1 angle and TM arthrodesis in an increasingly palmarly abducted position. CONCLUSIONS: Radial collateral ligament laxity of thumb MCP joint was exacerbated after TM arthrodesis. Greater fixation angle in palmar abduction resulted in more laxity of the joint. TYPE OF STUDY/LEVEL OF EVIDENCE: Prognostic IV.
