Boutonnière Deformity

Bent Middle Joint, Straight Tip

Disruption of the central slip of the extensor tendon at the PIPJ, causing PIPJ flexion and DIPJ hyperextension. The lateral bands sublux volarly, becoming flexors of the PIPJ and hyperextensors of the DIPJ. Can be traumatic (jam injury, laceration) or secondary to RA. Named for the "buttonhole" appearance of the head of the proximal phalanx poking through the torn central slip.

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