The lateral band of the finger extensor mechanism is one of two lateral slips arising from the central slip bifurcation distal to the MCP joint, running along the lateral aspect of the proximal phalanx and PIP joint to fuse with the contralateral lateral band beyond the PIP joint, forming the conjoint lateral band that inserts on the distal phalanx base. The interossei and lumbricals contribute to the lateral bands, allowing the intrinsic muscles to extend the IP joints while the extrinsic EDC extends the MCP joint.
Lateral band pathology is central to two key finger deformity patterns: Boutonniere deformity (central slip rupture allows the lateral bands to migrate palmarly relative to the PIP joint axis, converting them from extensors to flexors of the PIP joint while hyperextending the DIP); and swan-neck deformity (PIP hyperextension from volar plate laxity allows the lateral bands to migrate dorsally, creating a deformity opposite to boutonniere). Lateral band release (Dolphin procedure) corrects swan-neck deformity by releasing the lateral band proximal to the oblique retinacular ligament.
Central slip rupture allows the lateral bands to slip palmarly past the PIP joint axis converting from PIP extensors to PIP flexors, producing the boutonniere deformity with fixed PIP flexion and DIP hyperextension; early splinting of the PIP in extension for 6 weeks maintains central slip healing and prevents lateral band contracture in the deformed position.
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