Impingement of the flexor pollicis longus tendon by an enlarged radial seasamoid causing trigger thumb: A case report

Painfut snapping with flexion and extension of the thumb is usually associaled with stenosing tenosynovitis of the flexor pollicis longus (FPL) tendon at the level of the A1 pulley. Enlargement of the FPL is believed to occur secondary to irritation by the sl~notic entrance of the fibrous flexor sheath, leading to disproportion in size between the flexor tendon and its sheath. Secondary triggering can be seen in rheumatoid arthritis, gout, and metabolic disorders such as diabetes that cause connective tissue changes. Other less commoll causes of triggering include tumors of the tendon sheath, a loose body in the metacarpophalangeal (MP)joint, aM entrapment of the collateral ligaments by an osteophyte on the metacarpal head. We present a case of trigger thumb after a hyperextension injury in which the tendinous initation and fibrolic enlargement were caused by impingement of a hypertrophic radiaI sesamoid against the FF'L.