Extensor Expansion Hood Under the Skin, Posterior View

Description

Seen beneath the dorsal skin of an adult male hand, the extensor expansion (dorsal hood) spreads distally over the metacarpophalangeal joint, where the extensor digitorum communis tendon flattens into a broad aponeurosis before dividing into a central slip and paired lateral bands on the proximal phalanx. Sagittal bands cradle the tendon on the dorsum of the metacarpal head, while intertendinous connections (juncturae tendinum) link adjacent extensor tendons proximally. Intrinsic muscles insert into this mechanism, with dorsal interossei and lumbricals blending into the lateral bands on the radial and ulnar sides of each digit. Bones of the metacarpals and phalanges sit deep to the tendinous sheet, and an extensor retinaculum at the wrist retains the extensor compartments as they pass into the hand. Clear landmarks. This posterior perspective matters because most finger extension problems are failures of the extensor hood, not simple tendon rupture. A sagittal band tear at the MCP joint allows ulnar subluxation of the extensor digitorum tendon, a common post-traumatic cause of painful snapping and loss of active MCP extension, and the anatomy here explains why it worsens with flexion. Distally, disruption of the central slip with volar migration of the lateral bands produces boutonniere deformity, while terminal tendon injury at the distal phalanx produces mallet finger, both patterns that make sense only when you track the dorsal aponeurosis across the PIP and DIP joints. Use this plate for gross anatomy labs, hand surgery teaching files, and orthopaedic or plastics publications describing extensor tendon zones, sagittal band repair, or boutonniere reconstruction, where readers need the aponeurotic layout under the skin rather than a superficial skin rendering. It also supports clinical skills content on extensor tendon testing and splinting strategy by relating joint posture to hood mechanics. Anatomical accuracy verified by SciePro's Medical Advisory Board.