Improving Metacarpophalangeal Joint Instability by Joint Implantation in Parallel From a Supernumerary Thumb in Severely Hypoplastic Duplicated Thumbs.

ABSTRACT Here, we present 2 cases of a severely hypoplastic duplicated thumb classified as Wassel types 5 and 6 and discuss whole-joint implantation from a supernumerary thumb as an alternative to stabilize the hypoplastic metacarpophalangeal (MCP) joint. The aim of the surgical treatment of thumb polydactyly is to reconstruct a functional and aesthetically pleasing thumb. Hypoplasia of joint components and abnormal tendon alignment lead to unpleasing results with angular deformity of the reconstructed thumb. In 2 cases, the MCP joint of the dominant digit was hypoplastic and unstable in all directions. The main problem was underdevelopment of the affected MCP joint, and it was reasonable to attempt to stabilize the unstable joint by adding another redundant joint in parallel. Whole-joint implantation with a flap on a vascular pedicle is useful to repair both joint instability and soft tissue hypoplasia, as in case 1. The vascularized joint can maintain balanced growth potential. However, nonvascularized interphalangeal (IP) joint implantation is a simple solution for repairing MCP joint instability, as in case 2. These joints have no tendon insertions, so we believe they are acting as a splint supporting the hypoplastic joint for a long period. The transfer of composite tissues from the foot has been reported for reconstruction of finger and thumb hypoplasia. Duplicated thumb operation is usually recommended at 1 year old. Similarly, nonvascularized joint implantation in parallel may be a promising choice to overcome MCP joint instability and to maintain range of motion in hypoplastic cases with a duplicated thumb.In conclusion, joint implantation in parallel from a supernumerary thumb could prevent angular deformity and is an alternative to overcome MCP joint instability in cases of a severely hypoplastic duplicated thumb without any donor morbidity.