What is the diagnosis and treatment for stenosis of the flexor pollicis longus (FPL) tendon?

From the Guidelines

Stenosing tenosynovitis of the flexor pollicis longus tendon, also known as trigger thumb, is best diagnosed and evaluated using MRI, which allows for accurate assessment of tendon injuries, pulley system lesions, and associated injuries. The condition occurs when the flexor pollicis longus tendon becomes inflamed and thickened, causing it to catch in the surrounding sheath, particularly at the A1 pulley, creating a characteristic triggering or locking sensation during thumb movement 1.

Diagnosis and Evaluation

• MRI is ideal for evaluating tendon injuries and helping with surgical planning, with a sensitivity of 92% and specificity of 100% for diagnosis of flexor tendon injuries, as reported by Rubin et al 1.
• MRI can accurately depict the pulley system, particularly the A2 and A4 pulleys, with lower sensitivity for A3 and A5 pulleys, and can directly identify A2 and A4 pulleys in 100% of cases, as reported by Hauger et al 1.
• Dynamic US can also be used for initial evaluation, but MRI is preferred for its high sensitivity and specificity in diagnosing tendon injuries and pulley system lesions.

Treatment Approach

• Initial management includes rest, NSAIDs like ibuprofen (400-600mg three times daily) or naproxen (250-500mg twice daily) for 1-2 weeks, and splinting of the thumb in a neutral position for 4-6 weeks, particularly at night.
• Corticosteroid injections into the tendon sheath (typically methylprednisolone 20-40mg mixed with lidocaine) can provide significant relief for moderate cases, with effects lasting several months.
• Physical therapy focusing on gentle stretching and strengthening exercises should be incorporated once acute pain subsides.
• For cases resistant to conservative treatment after 3-6 months, surgical release of the A1 pulley is recommended, which has a high success rate of over 90% 1.

Importance of Early Intervention

Early intervention is crucial to prevent permanent contracture or disability of the thumb. If pain persists despite a well-managed conservative treatment trial, referral to an orthopedic surgeon for surgical evaluation may be warranted 1.

From the Research

Stenosis of the Flexor Pollicis Longus Tendon

• Stenosis of the flexor pollicis longus (FPL) tendon is a condition that can cause trigger finger or thumb, as seen in a study on corticosteroid injection therapy for trigger finger or thumb 2.
• The FPL tendon can be affected by various conditions, including tendon rupture, which can be treated with step cut lengthening, a single-stage reconstruction technique without the need for tendon grafting or tendon transfer 3.
• The position of the FPL tendon in relation to the FPL plate and distal radius width is important to consider in order to prevent tendon-plate contact and reduce the risk of tendon rupture 4.
• Entrapment of the FPL tendon can occur after minimally invasive plate osteosynthesis of a distal radius fracture, and revision surgery and tendon repair may be necessary to restore FPL function 5.
• A study on six-strand flexor pollicis longus tendon repairs with and without circumferential sutures found that the six-strand repair technique is an effective procedure to assure early active motion after FPL tendon injuries, and good results can also be achieved by omitting the circumferential suture 6.

Treatment Options

• Corticosteroid injection therapy is a safe and effective treatment option for trigger finger or thumb, with a recurrence rate of 20.3% and an average injection efficacy of 315 days 2.
• Step cut lengthening is a surgical technique that can be used to treat FPL tendon rupture, and it has been shown to be a effective procedure in reconstructing the tendon defect 3.
• Revision surgery and tendon repair may be necessary to restore FPL function in cases of tendon entrapment after minimally invasive plate osteosynthesis of a distal radius fracture 5.

Prevention

• The position of the FPL plate and distal radius width should be carefully considered in order to prevent tendon-plate contact and reduce the risk of tendon rupture 4.
• The use of an indentation in the FPL plate can reduce tendon-plate contact and ideally even prevent it entirely, and ulnar positioning of the plate can lower the risk of tendon-plate contact 4.