Extensor Tendon Repair: Zone III

A boutonnière’s deformity is caused by disruption of the central slip of the extensor tendon mechanism at the PIP joint. Disruption of the central slip results in a change in pull of the interosseous and lumbrical muscles from the central slip to the lateral bands, which over time causes the lateral bands to migrate volarly and eventually contract if not treated. This volar migration of the lateral bands pulls the PIP joint into a flexed posture. Additionally, secondary shortening of the oblique retinacular ligaments results in hyperextension of the distal phalanx.