Blauth II thumb hypoplasia: a management algorithm for the unstable metacarpophalangeal joint

Blauth Type II thumb hypoplasia is defined by first web space narrowing, deficiency of thenar musculature, and instability of the metacarpophalangeal joint (MCPJ). This instability can be uni-axial (type IIA) or multi-axial (type IIB). The aim of this study was to assess the results of treating type II thumb hypoplasia using an algorithm based on the type of instability present. Cases of uni-axial MCPJ laxity (type IIA) underwent stabilization as part of a flexor digitorum superficialis opposition transfer. Type IIB cases with multi-axial instability were treated with an MCPJ chondrodesis and an abductor digit minimi transfer for opposition. First web space release was achieved using a z-plasty approach in all patients. An analysis was carried out of all cases of type II thumb hypoplasia treated by the senior author within the setting of a tertiary referral children's hospital over a 9 year period. Using our management algorithm, equivalent functional results were seen in each subgroup in terms of first web space release, MCPJ stabilization, and opposition.