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Extensor Hood

aponeurosis extensoria digitorum

The extensor hood is the complex fibrous expansion over the dorsum of each finger that integrates the force of the long extensor, interossei, and lumbricals into coordinated finger extension. The long extensor contributes the central portion extending the MCP joint, the interossei contribute oblique lateral bands to extend the IP joints, and the lumbricals insert into the lateral bands to produce the intrinsic plus posture. Disruption of any part of this mechanism produces predictable deformity.

Region: Hand & Wrist

Biomechanics

Function & Actions

Integrates extrinsic extensor and intrinsic muscle forces for precise finger extension at all joints

Clinical Relevance

Clinical Notes

Sagittal band rupture at the MCP joint level allows the extensor tendon to sublux ulnarward off the knuckle, producing a painful snapping finger that fails to extend the MCP from the flexed position. This is common in rheumatoid arthritis and from direct trauma. Boutonniere deformity from central slip disruption and swan neck deformity from volar plate laxity both reflect extensor hood component failures.

Pathology

Common Injuries & Conditions

Sagittal Band Rupture

Extensor tendon subluxation off the MCP knuckle from sagittal band disruption producing painful snapping and MCP extension lag, managed with extension splinting in acute cases and surgical repair for chronic instability.

Swan Neck Deformity

PIP hyperextension and DIP flexion from volar plate laxity or intrinsic muscle tightness, producing a swan neck finger shape requiring splinting or surgical correction for functional impairment.