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Extensor Hood (Digital)

expansio extensoris digitorum

The extensor hood (dorsal aponeurosis) is the complex fibrous expansion at each finger that integrates the extrinsic EDC with the intrinsic interossei and lumbricales into a mechanical system capable of producing coordinated MCP and IP motion. The central slip extends the PIP; the lateral bands extend the DIP. The intrinsic muscles through the hood produce MCP flexion and IP extension simultaneously — the intrinsic plus position.

Region: Hand & Wrist

Biomechanics

Function & Actions

Integrates intrinsic and extrinsic muscle forces into coordinated finger extension and IP flexion-extension

Clinical Relevance

Clinical Notes

Boutonnière deformity from central slip rupture allows the lateral bands to migrate volar to the PIP joint axis, converting them from PIP extensors to PIP flexors while simultaneously tightening the terminal tendon to hyperextend the DIP. Swan neck deformity is the reverse — PIP hyperextension and DIP flexion from imbalanced intrinsic tightness or volar plate laxity.

Pathology

Common Injuries & Conditions

Boutonnière Deformity

Central slip disruption allowing lateral band migration producing PIP flexion and DIP hyperextension managed with PIP extension splinting acutely.

Swan Neck Deformity

PIP hyperextension and DIP flexion from intrinsic tightness or volar plate laxity managed with silver ring splints or PIP joint tenodesis.