The false cortical thumb.

Two cases of thumb-in-palm deformity are presented that are postulated to be complications of repeated radial artery puncture and cannulation with secondary damage to the thumb extensor tendon sheath and its extensor pollicis brevis and abductor pollicis longus tendons. Nonfixed adduction-flexion posturing of the thumb is to be differentiated from "the cortical thumbs" often associated with adduction, flexion contracture of upper motor neuron injury, and other disorders with thumb-in-palm deformities. The risks of complication of radial artery puncture are multiple. An added risk is the potential for impaired extensor tendon function as a complication of a radial puncture.