The lateral bands of the finger extensor mechanism are paired fibrous bands running from the dorsolateral surface of the proximal phalanx distally to converge on the terminal tendon at the DIP joint. They receive contributions from the lumbrical and interosseous muscles medially. The lateral bands are held in position by the transverse retinacular ligament volarly and the triangular ligament dorsally near the DIP level, forming the lateral slips of the extensor hood.
Extend the DIP joint as the primary extensor mechanism at the distal joint. Contribute to PIP extension when the intrinsics contract through the interosseous insertion, and are the basis of the intrinsic-plus position.
The lateral bands are the key structures in mallet finger (terminal extensor tendon disruption at the DIP level), boutonniere deformity (lateral band volar subluxation at the PIP level), and swan-neck deformity (lateral band dorsal subluxation). In trigger finger surgery, the lateral bands define the dorsal limit of safe tendon sheath incision. Zone 3 extensor tendon injuries affecting the central slip allow volar migration of the lateral bands, producing the boutonniere deformity.
Forced DIP flexion against resistance ruptures the terminal extensor tendon including the converging lateral bands from the distal phalanx, producing inability to actively extend the DIP joint, managed by continuous DIP extension splinting for 6-8 weeks.
Central slip rupture at the PIP joint allows the lateral bands to migrate volarly and act as PIP flexors, producing the boutonniere deformity of PIP flexion and DIP hyperextension, requiring early splinting or surgical repair and lateral band repositioning.
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