Boutonnière deformity

The boutonnière deformity develops over one to three weeks following acute central-slip disruption. As the lateral bands migrate volar to the PIP joint axis they lose their extensor effect at the PIP and exert hyperextension force at the DIP via the terminal tendon. The PIP fixes in flexion while the DIP is pulled into hyperextension. Acute closed central-slip injury is managed with full PIP extension splinting for six weeks; an established deformity is more difficult to address surgically because correction of PIP extension reliably trades extension for a flexion deficit.