Reinsertion of the Extensor Pollicis Brevis for Correction of Z-Deformity in Advanced Thumb Carpometacarpal Osteoarthritis

Thumb carpometacarpal (CMC) osteoarthritis in advanced stages is frequently associated with metacarpophalangeal (MCP) hyperextension, resulting in the characteristic Z-deformity and reduced pinch stability. Standard basal joint reconstruction may fail to correct MCP hyperextension, contributing to persistent functional impairment. Prosthetic trapeziometacarpal arthroplasty may partially correct Z-deformity but becomes unreliable when MCP hyperextension exceeds 30 degrees. This article describes a reproducible surgical technique combining trapeziectomy, APL suspension arthroplasty, and EPB reinsertion onto the dorsal aspect of the first metacarpal head to restore sagittal balance of the MCP joint. In this configuration, the EPB is intentionally converted from an active extensor into a passive dorsal stabilizer, providing a tenodesis-like restraint against hyperextension while preserving flexion arc. In 10 consecutive patients with Eaton-Littler stage III-IV disease and MCP hyperextension ≥30 degrees, mean hyperextension improved from 38.6 degrees preoperatively to 5.4 degrees at 12-month follow-up, with preservation of MCP flexion and improvement of key pinch strength and QuickDASH scores. This approach provides stable correction of MCP hyperextension while maintaining MCP motion, offering a motion-preserving alternative to capsulodesis or arthrodesis.