Extensor Expansion Hood, Posterior View

Description

Dorsal hand anatomy is centered on the extensor expansion (dorsal digital expansion, extensor hood), a triangular aponeurosis formed by the extensor digitorum tendon as it crosses the metacarpophalangeal (MCP) joint and spreads distally over the base of the proximal phalanx. From this posterior perspective, the central slip continues in the midline toward the base of the middle phalanx, while paired lateral bands track along the dorsolateral margins of the proximal phalanx before converging toward the terminal tendon at the distal phalanx. Proximally, sagittal bands tether the extensor tendon to the volar plate and MCP joint capsule, keeping the tendon centered over the metacarpal head as the digit flexes and extends. Small structures matter. Clinically, this view helps you teach why disruption at different levels produces different deformities: a central slip injury at the PIP joint can lead to boutonniere deformity, whereas terminal tendon failure at the DIP joint produces mallet finger. Sagittal band rupture, common after a “boxer’s knuckle” injury to the MCP joint, permits ulnar or radial subluxation of the extensor tendon and causes painful snapping during finger motion, a finding that makes sense only when you appreciate how the hood wraps around the proximal phalanx and anchors to collateral ligament complex and volar plate. The relationship between the lateral bands, the triangular ligament dorsally, and the oblique retinacular ligament volarly explains why edema and scarring after trauma can quickly convert a tendon laceration into a stiff PIP flexion contracture with secondary DIP hyperextension. Use this illustration for upper limb anatomy labs, hand surgery teaching decks on extensor tendon zones (V to VII), and rehabilitation materials explaining splinting strategies for boutonniere and mallet injuries. It also fits well in textbooks discussing dorsal hand lacerations and extensor mechanism repair. Anatomical accuracy verified by SciePro's Medical Advisory Board.