Historical Overview
- Pediatric trigger thumb is a fixed-flexion deformity of the interphalangeal (IP) joint of the thumb. It represents a distinct clinical entity from trigger thumb in adults, and must therefore be diagnosed and treated independently.1,2
- Although the precise etiology of pediatric trigger thumb remains somewhat controversial, there have been substantial improvements in understanding its etiology over the past 20 years.2
- It was originally believed that pediatric trigger thumb was congenital, but current evidence suggests that it is an acquired condition.1
Description
- Pediatric trigger thumb can be diagnosed with a physical examination of the affected thumb, as patients who have the condition will hold the thumb in flexion at the IP joint—up to 90°—and possibly display difficulty extending this joint as well.
Pathophysiology
- Most experts agree that this disorder results from a mismatch in the size of the flexor pollicis longus (FPL) tendon and the A1 pulley, which disrupts normal tendon gliding.2,3
- The size mismatch may be due to a thickening of the FPL—or Notta’s nodule—which prevents the FPL from passing under the thumb’s A1 pulley and results in fixed flexion of the thumb. The cause of the nodule is unknown but may be linked to metacarpophalangeal (MP) joint mobility and volar plate laxity in toddlers.
- The size mismatch may also be due to pathological changes in the flexor sheath, such as a stenosis of the tendon sheath similar to the pathogenesis in adults.1
- Some have suggested that the constant flexed position of the thumb during the prenatal and neonatal periods results in collagen degeneration and synovial proliferation, which produces a FPL nodule and thickening of the tendon sheath.2
- Pediatric trigger thumb typically presents at ~2 years of age, but can go unnoticed for years in some patients. Parents may report a history of triggering followed by development of a fixed-flexion contracture. Although there is rarely a history of trauma or injury, children are often mistakenly referred to an orthopedic surgeon for evaluation of thumb fracture or IP joint dislocation.2,4
Instructions1-3
- Obtain an accurate and complete patient history.
- Palpate the base of the patient’s affected thumb and note the presence of any large mass or nodule.
- With the patient’s hand at rest, perform an examination of the affected thumb and note its flexion/extension position.
- Ask the patient to actively extend the IP joint of the affected thumb.
- Look for any signs of difficulty during thumb extension.
Variations
- Clinicians should also check the patient’s other thumb during the evaluation to detect for bilateralism. Although the other thumb may not be stuck in a flexed position, a nodule may be felt in the contralateral hand.3
Related Signs and Tests2,3
- Differential diagnosis for pediatric trigger thumb:
- Clasped thumb
- Thumb fracture
- Thumb IP joint dislocation
- Developmental loss of the extensor tendon
- Arthrogryposis
- Cerebral palsy
- Radiographic assessment of pediatric trigger thumb is rarely needed because the diagnosis can usually be made by with the patient history and physical examination alone.2
Diagnostic Performance Characteristics
- If the patient’s thumb is locked in flexion at the IP joint, it can usually be partially corrected on the examination. Some patients also demonstrate difficulty actively extending the IP joint of the thumb, with clicking or snapping during attempted extension. In other instances, the thumb may “catch” and then eventually move to full extension.2,3
- The nodule that may be felt at the base of the thumb is usually firm and fixed at the volar side just proximal to the thumb MP joint. While palpating the nodule, motion of the thumb should be attempted and total range of motion allowed should be recorded.3,4
- Clinicians should also check that the thumb is well perfused and the child is moving it spontaneously.3
