Radiological evaluation of ulnar thumb metacarpophalangeal ligament reconstruction for chronic thumb instability in cadavers

Abstract

Various techniques have been described to restore metacarpal stability in the thumb. Ligament reconstruction techniques that position the bone tunnels in a triangular configuration, with the apex proximally, are optimal for stabilizing the metacarpophalangeal (MCP) joint, while preserving the thumb's range of motion. Using an interference screw ensures this reconstruction is as strong as the native ligament. Our purpose was to evaluate a new technique designed to treat cases of chronic thumb instability. We created metacarpal instability in 10 fresh cadaver forearms by sectioning the ulnar collateral ligament (UCL). Ulnar thumb MCP ligament reconstruction (UTMP) was performed in five thumbs and Littler reconstruction in the other five. Radiographic analysis was performed after ligament transection and after ligament reconstruction to compare MCP angles on posterior-anterior (MCPFA) and lateral views (MCPLA), and to evaluate MCP congruence and sesamoid bone parallelism. After UCL transection, thumb instability was present in all cadaver specimens. A significative increase in the MCPFA value was found: Littler (P=0.01) and UTMP (P=0.01). The MCPFA with thumb loading was not significantly changed with the Littler (P=0.83) or UTMP (P=0.46) relative to pre-transection. All parameters were significantly improved, reflecting a return to normal values. There was no significant difference between the two reconstruction techniques. Based on the findings in this cadaver study, UTMP reconstruction appears to correct the radiologic features of lateral thumb instability. It is a simple technique that restores MCP stability without limiting MCP flexion. Type of study/level of evidenceTherapeutic IV.