Previous studies have demonstrated that outcomes for the ulnar digits appear to be worse than those of the radial digits after silicone metacarpophalangeal joint arthroplasty (SMPA) for the rheumatoid hand. This study examines various components of hand deformities in an effort to understand SMPA outcomes in terms of metacarpophalangeal (MCP) joint range of motion and alignment. We hypothesize that the ulnar fingers will have less improvement, marked by greater ulnar drift, extension lag, and less MCP joint arc of motion than the radial fingers.

Sixty-eight surgical patients were recruited from 3 sites in this multicenter, international prospective cohort study. All patients had a diagnosis of rheumatoid arthritis, were between the ages of 18 and 80, and were eligible to have SMPA based on measured hand deformities (extensor lag and ulnar drift). Ulnar drift, extension lag, and arc of motion for the MCP joint of each finger were measured at baseline (before surgery) and 1 year after SMPA.

All fingers showed an improvement in ulnar drift from baseline to 1 year after surgery. The smallest improvement was in the index finger, and the largest improvement was in the little finger. Similarly, the largest improvement in extension lag was seen in the little finger, and the smallest improvement was seen in the index finger. In terms of MCP joint arc of motion, all fingers moved to a more extended posture and gained an improved arc of motion, but the biggest improvement was observed in the 2 ulnar fingers and less in the 2 radial fingers.

Our hypothesis that the ulnar fingers would have worse outcomes than the radial fingers was not proven by this study. Although experiences have indicated that it is more difficult to maintain posture for the ring and little fingers after SMPA owing to the deforming forces, sufficient correction of the deformities in the ulnar fingers is possible, if adequate bone resection and realigning of the extensor mechanism are carefully performed during the procedure.

Prognostic I.