ABSTRACT
The characteristic deformity that occurs when muscles acting on the thumb are spastic is the thumb-in-palm deformity. This deformity may be due to spasticity of the intrinsic muscles of the thumb, spasticity and weakness of the extrinsic muscles of the thumb or a combination of both. As a consequence of spasticity of the adductor pollicis the thumb remains adducted. In order to grasp a large object in the palm the thumb needs to abduct while the hand is positioned over the object and then the thumb has to adopt a position of opposition in order to grasp the object. The most common operation performed for an adducted thumb is the release of the adductor pollicis from its origin. An incision is made in the thenar crease and the adductor pollicis muscle can be identified simply by retracting medially the flexor tendon to the index finger.
