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.
| Muscle |
|
|---|---|
| Attachment | Middle and distal phalanges via central slip (middle phalanx) and terminal tendon (distal phalanx) |
Integrates extrinsic extensor and intrinsic muscle forces for precise finger extension at all joints
The sagittal bands at the MCP joint keep the extensor tendon centred over the knuckle. Their rupture, usually of the radial band from a direct blow (boxer's knuckle) or rheumatoid attrition, allows the tendon to sublux ulnarward, producing a painful snapping finger that fails to extend the MCP from the flexed position. Boutonnière deformity from central slip disruption and swan neck deformity from volar plate laxity or intrinsic tightness both reflect failures of other hood components.
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.
Central slip disruption allowing palmar lateral band migration, producing PIP flexion and DIP hyperextension, managed with PIP extension splinting acutely.
PIP hyperextension and DIP flexion from volar plate laxity or intrinsic muscle tightness, producing a swan neck finger shape, managed with ring splints or surgical correction for functional impairment.
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