A Novel Method for Achieving Metacarpophalangeal Joint Stability in Cases of Unstable Thumb Duplication: A Report of Two Cases.

Two factors contribute to the stability of the thumb: static stability provided by the bones, joints, and ligaments, and dynamic stability provided by the muscles. Proximal types of polydactyly, such as Wassel types Ⅴ and Ⅵ, are often associated with thenar dysplasia, which is thought to lack sufficient dynamic stability. Therefore, in cases of proximal polydactyly where instability at the metacarpophalangeal (MCP) joint is severe, static stability becomes important. No reports have been published on ligament reconstruction during primary collateral ligament reconstruction for thumb polydactyly, a pediatric congenital difference. We achieved good midterm results with the reconstruction of the ulnar collateral ligament of the MCP joint using the spare flexor pollicis longus tendon for MCP joint instability. This procedure may be an option for MCP joint stabilization in patients with primary surgery presenting MCP joint ulnar instability.