Dual-purpose extensor pollicis longus transfer for combined type I and IV rheumatoid thumb deformities.

The Nalebuff classification, widely used by hand surgeons, describes six different canonical patterns. However, combined deformities are rarely reported, despite their significant impact on surgical decision-making. We present a dual-purpose extensor pollicis longus (EPL) transfer designed to address combined type I Boutonnière deformity and type IV metacarpophalangeal (MP) joint ulnar instability in rheumatoid thumb deformities. In two cases, a transosseous tunnel was drilled from dorsal to ulnar at the base of the proximal phalanx of the thumb, allowing passage and dorsal fixation of the EPL tendon. The remaining EPL tendon was then anchored at the ulnar side of the metacarpal head to reconstruct the ulnar collateral ligament. This dual-purpose transfer restores active thumb extension and simultaneously stabilizes the MP joint, thereby eliminating compensatory adduction at the first carpometacarpal joint.