The deformity of thumb in ulnar paralysis.

The flexion/extension angles at the Metacarpophalangeal and Interphalangeal joints of the thumb in position of rest and pinch were studied in 68 thumbs of ulnar paralysis. In two thumbs the flexor pollicis brevis was not paralysed. Twenty five normal thumbs were used as controls for comparison. During the resting position the metacarpophalangeal joints showed less flexion and interphalangeal joints more flexion than normal. During the pinch position metacarpophalangeal hyperextension and interphalangeal flexion -- the Z deformity was seen in about 60% while marked interphalangeal flexion was seen in all thumbs of ulnar paralysis. It is suggested that this muscular imbalance is likely to affect thumb joints in time because of abnormal stresses due to altered forces and this can be prevented by restoring the muscle balance by surgery.