Trigger Thumb 

Painful triggering or locking of the thumb is a common malady that can significantly interfere with hand function and the performance of routine activities. Much less frequently, a similar condition may occur in children. Historically, this condition in children has been referred to as congenital trigger thumb.^[1] However, recent evidence indicates that it usually presents sometime after infancy; it is thus more appropriately referred to as pediatric trigger thumb.^[2] See the image below.

Recent cases and studies

Between 1994 and 2004, Li et al treated 7 children (9 thumbs; 3 right, 2 left, 2 bilateral) for trigger thumb with hyperextensible metacarpophalangeal anomaly (>60º) by surgical release of the first annular pulley (A1 pulley) and proximal advancement of the metacarpophalangeal volar plate. The patients had a mean age of 46 months at surgery (range, 26-82 mo); there were 4 girls and 3 boys; and mean follow-up was 64 months (range, 1-8 y). All patients at last follow-up had returned to full activity without limitation or pain, and none of the patients had a recurrence of triggering or metacarpophalangeal hyperextension deformity, demonstrating, according to the authors, that trigger thumb with concomitant metacarpophalangeal hyperextension deformity can be treated in children by A1 pulley release and advancement of the volar plate.^[2]

In a study of 93 trigger thumbs in 83 patients, Chao et al compared the results with miniscalpel-needle percutaneous release with that of steroid injection. At 12 months, 44 of the 46 trigger thumbs treated with the miniscalpel-needle release had satisfactory results (measured by visual analogue pain scale and patient satisfaction), but only 12 of 47 thumbs treated with steroid injection had satisfactory results. No nerve injuries occurred in either group.^[3]

Lange-Rieb et al presented long-term results of open operative treatment of trigger finger or trigger thumb in adults. Of the operations performed, 210 (76%) were for a single digit release and 76 (24%) for multiple digits. All operations were performed under tourniquet control with local anaesthesia as outpatient procedures using a transverse incision just distal to the distal palmar crease or on the flexor crease of the thumb at the metacarpophalangeal joint. At latest follow-up (average, 14.3 y), 234 patients were evaluated, with no complaints, and there were no serious complications, such as nerve transection or bowstringing or recurrence.^[4]

Triggering of the thumb occurs when focal degenerative changes within the flexor pollicis longus (FPL) tendon lead to a localized swelling that limits tendon excursion within the tendon sheath.

Frequency

In adults, triggering most commonly occurs in the thumb, long finger, and ring finger. Idiopathic trigger thumb is 4 times more likely to develop in women than in men, usually affects women in the fifth and sixth decades of life, and is often bilateral. Trigger digits in the pediatric population occur almost exclusively in the thumb.^[5]

Trigger thumb usually occurs idiopathically. It develops more frequently in individuals with diabetes and in patients with osteoarthritis. Trigger thumb is more likely to occur in an individual with any condition that causes proliferation of the tenosynovium, such as inflammatory arthritis, gout, or chronic infection (eg, fungus or atypical mycobacteria). Certain people appear more prone to tenosynovitic conditions; patients with trigger thumb are more likely to develop carpal tunnel syndrome and de Quervain disease. The roles of overuse and trauma in trigger thumb are controversial, although the condition does have a predilection for the dominant hand.

Triggering normally occurs when localized swelling of the flexor tendon at the level of the metacarpophalangeal (MP) joint causes the tendon to get caught under the A1 pulley of the flexor tendon sheath.^{[6, 7]} With greater constriction, the tendon nodule often suddenly sticks proximal to the sheath, causing the thumb to lock in flexion. Occasionally, the nodule may catch within the sheath, locking the digit in extension. Thickening and histologic changes occur within the A1 pulley; occasionally, a ganglion develops on the tendon sheath.

Trigger thumb in patients with rheumatoid arthritis or chronic infection is the result of diffuse proliferation of tenosynovium within the tendon sheath. This process can extend distal to the MP joint and, when severe, cause stiffness rather than intermittent triggering.

Patients initially present with painful clicking of the finger or popping of the proximal interphalangeal (PIP) joint. They may complain of morning stiffness of the fingers without frank triggering. More advanced involvement leads to locking, usually in flexion (occasionally in extension), which must be released by passive manipulation with the other hand. Long-standing cases may result in a stiff finger with diminished tendon excursion. In these cases, the physician must be suspicious of a trigger thumb based on history, as triggering may not be demonstrable when tendon gliding is decreased.

Examination reveals a tender nodule over the distal palm that moves with flexion and extension of the finger. The physician may appreciate crepitus or clicking. The patient may be able to demonstrate active locking or snapping of the interphalangeal (IP) joint; this should not be confused with subluxation of the finger.

Children with trigger thumb rarely complain of pain. They usually are brought in for evaluation when aged 1-4 years, when the parent first notices a flexed posture of the thumb IP joint. These children often demonstrate bilateral fixed flexion contractures of the thumb by the time they present to the physician.^[8]

Consider surgical release of the A1 pulley in the symptomatic patient in whom nonsurgical measures have failed. Conservative treatment is not appropriate in the patient who presents with a locked digit that cannot be passively extended; the thumb fixed in flexion requires surgical correction.

Recent studies demonstrate that more than 60% of pediatric trigger thumbs will resolve without surgery. Even those patients without complete resolution will gain some improved motion with observation or splinting. Thus, the exact role of surgery for pediatric trigger thumb is being reexamined.

The flexor anatomy of the thumb differs from that of the fingers. The FPL is a single tendon within the flexor sheath that inserts onto the base of the distal phalanx. The fibro-osseous sheath is comprised of 2 annular pulleys (A1 and A2) that arise from the palmar plates of the MP and IP joints, respectively. The oblique pulley, which originates from and inserts onto the proximal phalanx, is the most important pulley from a biomechanical perspective. The oblique pulley is approximately 10 mm in length, blending with a portion of the adductor pollicis insertion.

The digital nerves and arteries run parallel to the tendon sheath distally. At the level of the MP flexion crease, they lie just deep to the skin. Proximal to the A1 pulley, the radial digital nerve of the thumb crosses obliquely over the sheath.

Other conditions whose presentation may overlap with trigger thumb include osteoarthritis, partial laceration of the flexor pollicis longus (FPL) tendon, or a tendon tumor. A locked metacarpophalangeal (MP) joint or more distal tendon nodule may be confused with idiopathic triggering in the fingers but not in the thumb. The pediatric trigger thumb must be differentiated from fracture, dislocation, congenital absence of the extensor, and, less commonly, cerebral palsy or arthrogryposis.