Congenital Trigger Thumb

Earlier termed as congenital trigger thumb, stenosing tendovaginitis of the flexor pollicis longus, is a relatively rare deformity in which the fibrous tendon sheath is thickened and constricted. There is a palpable nodule on the volar aspect of the thumb in the region of the metacarpo-phalangeal joint (Notta’s nodule).

Approximately 3 per 1,000 children are diagnosed by the age of 1 years. Pediatric trigger thumb is separate entity than adult acquired trigger thumb. Male and females  are affected equally. About 25% are bilateral.

More favored term now is  pediatric trigger thumb as the presentation is  sometime after infancy.

Pathophysiology of Congenital Trigger Thumb

The incongruity of the tendon’s surface interferes with its normal gliding within its sheath. Snapping or triggering results from the blockage of the tendon prominence against the constricted sheath and the sudden release following application of passive force and passage past the obstruction.

Flexor pollicis longus tendon is thickened due to abnormal collagen degeneration and synovial proliferation. This causes increase in flexor pollicis tendon diameter, compared to the A1 pulley, causes disruption of normal tendon gliding

Triggering, clicking or snapping is observed by flexion or extension of the interphalangeal joint. In advanced stage, extension is not  possible and there is a fixed flexion deformity of the thumb in the interphalangeal joint.

The etiology is unknown.

Pediatric condition of the thumb that results in abnormal flexion at interphalangeal (IP) joint

Spontaneous resolution unlikely after age of 2 years old

Presentation of Congenital Trigger Thumb

Children with are brought in for evaluation when aged 1-4 years with complaint flexed posture of the thumb.

In most cases the thumb is locked in flexion, but occasionally it may be locked in extension. The nodule on thumb joint is not painful. The infant or child has no complaints. It is the infant or child has no complaints. It is the concern of the parents that brings the patient to the surgeon.

In about 25 percent of cases, the trigger thumb is noted at birth. This congenital form resolves spontaneously within 12 months in about 30 percent of cases.

Involvement is bilateral in about 50 percent of the cases noted at birth.

The childhood form develops later on, between 6 and 30 months of age, and has a spontaneous recovery rate of about 12 percent.

Differential Diagnoses of Congenital Trigger Thumb

The congenital trigger thumb must be differentiated from fracture, dislocation, congenital absence of the extensor, and, less commonly, cerebral palsy or arthrogryposis.

Imaging

Radiographs are usually normal. X-rays are also helpful to exclude osteoarthritis, fracture malunion, foreign body, or a large sesamoid bone that is affecting interphalangeal joint motion.

Treatment of Congenital Trigger Thumb

If trigger thumb is present at birth, approximately 30 % of children will recover spontaneously in one year. About  12 % of the trigger thumbs that develop at the age of 6- 30 months recover in six months.

Rest of them need surgical release. A pediatric trigger thumb which develops in child older than three years of age  would almost always require surgery.

If the cases which do not resolve spontaneously are not treated by age of four years, 50%  of them may fevelop fixed flexion contractures.

In a younger child, the  surgery should be considered if congenital trigger thumb is not resolved by 12 months of age. Most surgical procedures for congenital  trigger thumb can be postponed until the age of 2 yrs, but should  be operated before  3 yrs because of possible flexion contractures.

The surgery involves a transverse incision  below metacarpophalangeal joint flexion crease and excision of the A1 pulley is required [a pulley in course of tendon at that site]. Notta’s flexion tendon nodule will dissipate with time.

After surgery, active motion of the thumb is encouraged as soon as possible.

Complications after Surgery

• Digital nerve injury
• Infection
• Scar contracture
• Bow-stringing of flexor tendon

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