The lateral bands are the intrinsic contribution to the extensor mechanism, running dorsolateral to the PIP joint before reuniting to form the terminal tendon inserting on the distal phalanx. The triangular ligament dorsal to the PIP joint holds the lateral bands dorsal in extension. If the central slip is disrupted, the lateral bands migrate volar to the PIP axis, the boutonnière deformity mechanism.
| Muscle |
|
|---|---|
| Attachment | The lateral bands arise from the intrinsic muscles and join the extensor hood lateral margin to insert as the conjoined terminal tendon on the distal phalanx |
PIP and DIP joint extension through the intrinsic plus pathway; PIP stabilisation against the central slip
Boutonnière deformity from central slip disruption allows the PIP joint to buttonhole through the extensor hood while the lateral bands migrate palmar to the PIP axis, where they flex the PIP and hyperextend the DIP. Acute treatment requires PIP extension splinting for about 6 weeks to allow central slip healing, while chronic deformity requires central slip reconstruction and lateral band repositioning. Swan-neck deformity is the reverse pattern: with volar plate laxity or intrinsic tightness the lateral bands drift dorsally, producing PIP hyperextension and DIP flexion. Swan-neck deformity is managed with splints that block PIP hyperextension or with soft tissue reconstruction.
Central slip disruption causing lateral band volar migration producing PIP flexion and DIP hyperextension managed with PIP extension splinting or central slip reconstruction.
Dorsal migration of the lateral bands with PIP hyperextension and DIP flexion from volar plate laxity or intrinsic tightness, managed with ring splints or surgical correction.
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