Central slip

The central slip is the central limb into which the extensor mechanism divides at the proximal interphalangeal joint. It inserts on the dorsal base of the middle phalanx and extends the PIP joint. Acute disruption — by laceration or by jamming of the flexed PIP — produces an extensor lag at the PIP and, over one to three weeks, the boutonnière deformity as the lateral bands migrate volar to the PIP axis and the unopposed terminal tendon hyperextends the distal interphalangeal joint.