The Clinical Syndrome

Trigger thumb is caused by inflammation and swelling of the tendon of the flexor pollicis longus tendon as a result of compression by the head of the first metacarpal bone. Sesamoid bones in this region may also compress and cause trauma to the tendon. Trauma is usually caused by repetitive motion or pressure on the tendon as it passes over these bony prominences. If the inflammation and swelling become chronic, the tendon sheath may thicken, resulting in constriction ( Fig. 55.1 ). Frequently, nodules develop on the tendon, and they can often be palpated when the patient flexes and extends the thumb. Such nodules may catch in the tendon sheath and produce a triggering phenomenon that causes the thumb to catch or lock. Pathologic changes of the pulley mechanism also contribute to the triggering phenomenon ( Fig. 55.2 ). Trigger thumb occurs in patients engaged in repetitive activities, such as handshaking by politicians, or activities that require repetitive pinching movements of the thumb, such as playing video games, texting, or frequent card playing ( Fig. 55.3 ). It occurs more commonly in females and in those patients suffering from diabetes.

Axial specimen photograph demonstrates the flexor tendon (asterisk) as it resides in a fibroosseous canal, anchored to the bones of the fingers by thickened fibrous sheaths called the annular pulleys (arrowheads).

(From Ragheb D, Stanley A, Gentili A, et al. MR imaging of the finger tendons: normal anatomy and commonly encountered pathology. Eur J Radiol . 2005;56(3):296–306.)

Specimen from a pathologic pulley showing chondroid metaplasia (arrows) with cells that look like cartilaginous cells organized in nests. (Semithin section, toluidine blue stain; original magnification ×250.)

(From Sbernardori MC, Bandiera P. Histopathology of the A1 pulley in adult trigger fingers. J Hand Surg Eur . 2007;32(5):556–559.)

Trigger thumb is caused by microtrauma from repetitive pinching movements of the thumb.

Signs and Symptoms

The pain of trigger thumb is localized to the palmar aspect of the base of the thumb (unlike the pain of de Quervain’s tenosynovitis, which is most pronounced more proximally, over the radial styloid). The pain of trigger thumb is constant and is made worse with active pinching of the thumb. Patients note the inability to hold a coffee cup or a pen. Sleep disturbance is common, and patients often awaken to find that the thumb has become locked in a flexed position.

On physical examination, tenderness and swelling are noted over the tendon, with maximal point tenderness over the base of the thumb. Many patients with trigger thumb experience a creaking sensation with flexion and extension of the thumb. Range of motion of the thumb may be decreased because of pain, and a triggering phenomenon may be present. As mentioned earlier, patients with trigger thumb often have nodules on the flexor pollicis longus tendon.