Vertical Locking of the Thumb Metacarpophalangeal Joint from Metacarpal Osteophyte: A Case Report and Review of Literature

Vertical locking of the thumb metacarpophalangeal joint (MCPJ) is a very rare condition characterised by a flexion deformity at the MCPJ, accompanied by preserved interphalangeal joint motion. Most reported cases are associated with trauma in young adults, and degenerative causes, especially in the thumb, have not been documented. We present a case of a 52-year-old woman with a several-year history of intermittent locking of the left thumb in flexion, initially self-reducible, later requiring passive release. Intraoperatively, a volar osteophyte from the metacarpal head was noted, with the sesamoid displaced centrally and becoming mechanically trapped on the bony prominence during flexion. The osteophyte was carefully excised, resulting in immediate resolution of the locking. Degenerative locking of the thumb MCPJ is rare and may present insidiously. Awareness of underlying osteophyte impingement on the sesamoid complex is essential. Open surgical intervention with preservation of key anatomical structures leads to good functional outcomes. <b>Level of Evidence:</b> Level V (Therapeutic).