A 22-year-old man sustained closed dislocation of the hallucal interphalangeal joint (HIPJ). Painful limitation of movements persisted 2 months after closed reduction. Magnetic resonance imaging revealed dislocation of the hallucal interphalangeal joint sesamoid (HIPJS) from its intra-articular attachment on the superior surface of the plantar plate to an extra-articular subcutaneous location, plantar and lateral to the flexor hallucis longus tendon. The HIPJS was enucleated through a plantar approach, and the foot remains pain-free 18 months later.
This case represents an unusual combination of HIPJ dislocation and extra-articular dislocation of its sesamoid. Raised awareness of the HIPJS, its normal anatomical location, and configuration will avoid delayed diagnosis.