Spastic flexus-adductus thumb considerably decreases the function of the hand because of the loss of muscular control and the predominant adduction retraction of the thumb. The authors propose a new surgical technique of unipolar tenotomy of the adductor pollicis and first interosseous dorsalis muscles, which are then sutured end-to-end forming a single elongated adductor muscle. These two muscles act synergistically as they are innervated by the same branch of the ulnar nerve. In this way, two pathological muscles are transformed into a single functional muscle. The preservation of the insertion of the adductor pollicis prevents hyperextension of the metacarpophalangeal joint. The authors used this technique in nine patients with a good functional and aesthetic result.