The insertion of the adductor pollicis muscles is incised. All contracting tissues are excised. Usually, the first dorsal interosseous muscle and a part of the palmar fascia are involved.

The two muscles affected are the extensor pollicis brevis (EPB) and abductor pollicis longus (APL). These muscles lift the thumb and move it out to the side. De Quervain's tenosynovitis occurs ...