Of the five cases of congenital flexion-adduction deformity presented in this report, all were bilateral except Case 3. The patient in Case 3 had a congenital absence of the left thumb. In each instance of the deformity, the thumb was firmly clasped beneath the flexed fingers and did not exhibit active extension. Three patients also had an associated tightness of the web space between the thumb and index finger. All the patients had abnormal mobility of the metacarpophalangeal joints of their thumbs.

In three of the patients, seen one to three months after birth (Cases 1, 2, and 5), plaster immobilization gave excellent results. In the fourth patient, seen at the age of two years (Case 4), a fair to good result was achieved after three months' immobilization. In another patient, seen at age nine (Case 3), a fair result was obtained by fusion of the metacarpophalangeal joint of the thumb.

Congenital flexion-adduction deformity of the thumb should be corrected by plaster immobilization in functional position at the earliest possible time, before permanent joint and tendon changes occur. If active extension does not return, tendon transfer is indicated to restore active extension to the thumb.