Simulated extension osteotomy of the thumb metacarpal reduces carpometacarpal joint laxity in lateral pinch.

Overview

PURPOSE: To assess the effect of an extension osteotomy of the thumb metacarpal on thumb carpometacarpal (CMC) joint laxity with respect to the lateral pinch position. METHODS: Seven fresh-frozen specimens were dissected. The metacarpal, trapezium, and trapezoid were removed en bloc and rigidly fixed proximally and distally. The laxity of each specimen was measured by cyclically loading the CMC joint in a custom-built laxity testing device designed to allow relative movement of the trapezium and first metacarpal in 4 directions. The position of the CMC joint in lateral pinch was used as the baseline joint position. An extension osteotomy then was simulated by flexing the metacarpal base 30 degrees, thus placing the joint in the relationship it would assume if an extension osteotomy was performed and the specimen was positioned in lateral pinch. Laxity measurements then were repeated. RESULTS: The simulated extension osteotomy reduced laxity in all directions tested: dorsal-volar (40% reduction), radial-ulnar (23% reduction), distraction (15% reduction), and pronation-supination (29% reduction). CONCLUSIONS: The beneficial clinical effects of a thumb metacarpal extension osteotomy may be partially due to reduced joint laxity in the position of lateral pinch.