1. The end results of twenty-three intermetacarpal bone blocks performed on twenty patients are presented. The operation is indicated whenever there is paralysis of the flexor pollicis brevis, the opponens pollicis, and the abductor pollicis brevis muscles and when tendon transplantation to restore active opposition of the thumb is not feasible.
2. To ensure a successful result it is important to use a snugly fitted autogenous tibial-bone graft, to lay generous cancellous bone about each end of the graft, to abduct and rotate the first metacarpal into full opposition, and to maintain immobilization of the thumb in a plaster-of-Paris cast until definite, solid bone union is evident by roentgenogram.