Congenital trigger thumb or pediatric trigger thumb as it is called now is a condition that results in abnormal flexion at the interphalangeal joint. That is why it also called flexion contracture of the thumb.
It is a separate entity than the adult trigger thumb.
This occurs due to thickening and constriction of fibrous tendon sheath of flexor pollicis longus. There is a palpable nodule on the volar aspect of the thumb in the region of the metacarpophalangeal joint (Notta’s nodule).
Approximately 3 per 1,000 children are diagnosed by the age of 1 year and it affects males and females equally.
The condition is bilateral in about one-fourth of the cases.
The exact cause of the congenital trigger thumb is not known.
Most common cases are acquired types though some reports suggest autosomal dominance inheritance with variable penetration term congenital trigger thumb is now considered a misnomer.
Image Credit: Wikipedia
Pathophysiology
The thickened tendon and constriction of the fibrous sheath occurs due to abnormal collagen degeneration and synovial proliferation.
This leads to the incongruity of the tendon’s surface that interferes with its normal gliding within its sheath. Snapping or triggering results from the blockage of the tendon prominence against the constricted sheath and then sudden release following the application of passive force and passage past the obstruction.
In addition, thickening of the flexor pollicis longus tendon causes an increase in flexor pollicis tendon diameter, compared to the A1 pulley lesding to the disruption of normal tendon gliding.
Triggering, clicking or snapping is observed by flexion or extension of the interphalangeal joint. In the advanced stage, the extension is not possible and there is a fixed flexion deformity of the thumb in the interphalangeal joint.
Spontaneous resolution unlikely after the age of 2 years.
Types of Pediatric Trigger Thumb
Congenital trigger thumb has been divided into four types depending on the severity of the contition.
- TypeI
- Notta nodule is present but no triggering
- Type II
- Triggering is observed during active extension of the interphalangeal joint
- Type III
- Active extension of the interphalangeal is not possible
- Triggering is on passive extension of the interphalangeal joint.
- Type IV
- Passive extension of the interphalangeal joint is not possible. (Fixed flexion deformity.)
Clinical Presentation
Children 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 the thumb joint is not painful.
On examination, there would be flexion deformity at the interphalangeal joint. A nodule at the joint is prominently palpable near the metacarpophalangeal joint. Sometimes, the interphalangeal joint flexion makes it prominent.
The neurovascular examination is normal.
In about one-fourth of the cases, the trigger thumb is noted at birth. About 30% of cases resolve within a year.
As about 25% of cases have bilateral involvement, the thumb on the other side should also be evaluated.
Imaging
X_rays are not required for the diagnosis.X-rays are normal in this condition but are helpful to rule out any bony injury or joint deformity or a large sesamoid bone that is affecting interphalangeal joint motion.
Anteroposterior and lateral views are often sufficient.
Treatment of Congenital Trigger Thumb
About 30 % of congenital trigger thumb patients recover spontaneously in one year.
The surgery should be considered if the congenital trigger thumb does not resolve by 12 months of age. Most of the cases should be operated before 3 years otherwise there is an increased risk of possible flexion contractures.
Nonoperative Treatment
Passive Extension Exercises and Observation
passive thumb extension exercises can be done in very young children. These are not recommended for fixed deformities in older children.
Best results are obtained in children less than two years of age.
Intermittent Extension Splint
This is often the first line of treatment and often more successful. However, it is not indicated in fixed deformity, only the flexible one.
The splint is used to maintain interphalangeal joint hyperextension and prevent metacarpophalangeal joint hyperextension. The splint is used for 6-12 weeks.
Resolution is seen in more than 50% of the cases.
Operative Treatment
Operative treatment consists of the release of A1 pulley release. It is indicated in a fixed deformity that persists beyond 12 months of age.
The procedure involves a transverse incision below metacarpophalangeal joint flexion crease, identification of A1 pulley, and release of A1 pulley using sharp excision.
Notta’s flexion tendon nodule will dissipate with time.
After surgery, an active motion of the thumb is encouraged as soon as possible.
Digital nerve injury caution must be performed during release as digital nerves at high risk due to proximity to flexor tendon and A1 pulley
Complications after Surgery
- Digital nerve injury
- Infection
- Scar contracture
- Bow-stringing of flexor tendon
References
- Kikuchi, N.; Ogino, T. (2006). “Incidence and Development of Trigger Thumb in Children”. The Journal of Hand Surgery. 2006; 31: 541–43.
- Ogino, T. (). “Trigger Thumb in Children: Current Recommendations for Treatment”. The Journal of Hand Surgery. 2008; 33: 982–84.
- Baek, G. H.; Lee, H. J. (2011). The Natural History of Pediatric Trigger Thumb: A Study with a Minimum of Five Years Follow-up”. Clinic Orthop Surg; 3: 157–159.
- Jung, H. J.; Lee, J. S.; Song, K. S.; Yang, J. J. (2011). Conservative treatment of pediatric trigger thumb: Follow-up for over 4 years”. J Hand Surg (Eur); 37: 220–224.
- Vyas B.K. Sarwahi V. Bilateral congenital trigger thumb. Indian J Pediatr. 1999; 66: 949-951.
