Purpose To describe a fibrocartilaginous structure on the dorsal surface of the metacarpophalangeal (MCP) joint. Methods A combination of anatomical dissection, histology, ultrasound, and magnetic resonance imaging was undertaken to explore the anatomical structure described, with clinical correlation undertaken by surgical exploration of MCP joints. Results A dorsal structure of the MCP joint was identified as fibrocartilagenous in composition, triangular in shape, and - together with the volar plate and collateral and accessory collateral ligaments - forming a deepened dorsal fossa in which the metacarpal head invaginated. It was attached to the extensor tendon by loose connective tissue and formed part of the joint capsule. Conclusions The dorsal fibrocartilage of the MCP joint is a constant anatomical structure that appears to complement the structural support for the metacarpal head and extensor tendon. Possible functions include stabilization of the extensor tendon, formation of a dorsal fossa, prevention of extensor tendon attrition, and synovial fluid production. Its structure and function may have implications in future development of joint replacement devices. Clinical relevance This study adds to the collective knowledge about the precise anatomy of the MCP joint. Reconstructive surgery and, in particular, joint replacement surgery should consider the potential function and importance of this structure when designing interventions on the joint. ? 2015 American Society for Surgery of the Hand.