Roger Cornwall
DEFINITION
Pediatric trigger thumb is a condition in which tightness of the first annular (A1) pulley of the thumb and an enlargement or nodule of the flexor pollicis longus tendon interact to prevent normal thumb interphalangeal joint motion.
This condition appears distinct from pediatric trigger fingers and from adult trigger digits, although similarities in pathoanatomy and presentation have earned it its name.
The term “congenital trigger thumb” is a misnomer, as it has yet to be detected at birth in several large series prospectively examining a combined 14,581 newborns in three countries.10,14,17,19
ANATOMY
The flexor pollicis longus tendon courses through a flexor sheath in the thumb composed of a series of pulleys that prevent bowstringing of the tendon during thumb flexion.
The most proximal pulley is termed the A1 pulley, given its transverse annular nature. Division of this pulley does not cause bowstringing of the tendon during thumb flexion. The next pulley is the oblique pulley, although some authors have described an intervening distinct second annular pulley analogous to the A2 pulley in the fingers.2 These pulleys are important constraints against bowstringing.
The digital nerves to the thumb are in proximity to the flexor pollicis longus tendon sheath. The radial digital nerve obliquely crosses the tendon sheath just proximal to the A1 pulley, and the ulnar digital nerve runs parallel to the tendon immediately alongside the A1 pulley. Injury to these structures is possible during surgical release of the A1 pulley, so knowledge of the precise anatomy is important.
PATHOGENESIS
The pathogenesis of pediatric trigger thumb is unknown.
In adults, the pathogenesis of trigger digits has a predominantly inflammatory nature. However, in pediatric trigger thumb, biopsies have been unable to detect signs of inflammation by gross morphology or light or electron microscopy.3
A genetic predisposition has been considered, especially in cases of bilateral trigger thumb, but a genetic cause for the condition is not established.23
Traumatic etiologies have been proposed, but with no clear data to support this theory.
NATURAL HISTORY
The natural history of pediatric trigger thumb has been a focus of recent attention. The earliest reports of the condition described spontaneous resolution as rare, but newer reports have described spontaneous improvement rates of 24% to 63%.1,5,15
The most recent study1 regarding the natural history of pediatric trigger thumb reported a 63% resolution rate, although the definition of resolution was improvement in passive interphalangeal joint extension to neutral, not to the normal hyperextension. Furthermore, the average time to reach this improvement was 48 months from diagnosis.
Therefore, when considering the use of observation to treat a pediatric trigger thumb, the clinician should inform the parents that the thumb motion will improve but not return to normal, and that such improvement will take an average of 4 years.
PATIENT HISTORY AND PHYSICAL FINDINGS
Children typically present from late infancy through 5 years of age with painless loss of motion at the interphalangeal joint. The “triggering” phenomenon that so commonly occurs in adults is rare in children.
Parents will usually be unable to determine how long the condition has been present. Some parents will describe a preceding traumatic injury to the thumb, although such an injury may simply call the parents' attention to the thumb closely enough to notice a pre-existing trigger thumb.
Functional impairment and pain are unusual complaints, except in the case of active triggering.
The typical physical examination finding is a flexion contracture of the thumb interphalangeal joint, as the nodule in the flexor pollicis longus tendon typically lies proximal to the A1 pulley, preventing distal excursion of the tendon and extension of the interphalangeal joint (FIG 1A).
In a few cases, the nodule lies distal to the A1 pulley and the thumb rests in an extended position with the child unable to actively flex the interphalangeal joint. In this case, the passive flexion of the interphalangeal joint is normal, but interphalangeal joint flexion will not occur by tenodesis with wrist extension.
In even fewer cases, the child will be able to actively “trigger” the thumb with active flexion and passive extension.
Regardless of the position of the thumb interphalangeal joint, a nodule is easily palpable (and even visible) in the flexor pollicis longus tendon in the region of the palmar digital crease (FIG 1B). The nodule can be felt to move proximally and distally with even the few available degrees of movement of the interphalangeal joint.
In longstanding cases of fixed flexion deformity, thumb metacarpophalangeal joint hyperextension laxity is common. In other cases, a coronal plane deformity resembling clinodactyly may be present, although a causative relationship has yet to be established.
Because of the possibility of bilateral involvement, both thumbs should be examined.
An upper limb neurologic examination should be performed, including an assessment of tone in the intrinsic muscles of the hand, since the thumb-in-palm deformity of cerebral palsy can be confused with trigger thumb.
FIG 1 • A. A typical pediatric trigger thumb locked in flexion. Note the inability to passively extend the interphalangeal joint. B. A typical trigger thumb locked in flexion. Note the visibly protruding nodule in the flexor pollicis longus tendon at the level of the palmar digital crease. C,D. Congenital clasped thumb. C. The flexed resting posture of both the interphalangeal and metacarpophalangeal joints. D. The interphalangeal joint typically has full passive range of motion, while the metacarpophalangeal joint is fixed in flexion, differentiating congenital clasped thumb from pediatric trigger thumb.
Pediatric trigger thumb should not be confused with congenital clasped thumb, in which the metacarpophalangeal joint is fixed in a flexed position, with normal interphalangeal joint motion (FIG 1C,D).
IMAGING AND OTHER DIAGNOSTIC STUDIES
Radiographs are unnecessary in the clinically obvious case; if obtained, they only confirm the resting position of the thumb interphalangeal joint.
If the examination reveals signs of trauma (eg, swelling, ecchymosis), radiographs should be considered to rule out underlying skeletal injury.
Advanced imaging is unnecessary.
DIFFERENTIAL DIAGNOSIS
Congenital clasped thumb
Thumb-in-palm deformity (cerebral palsy)
Arthrogryposis
Thumb hypoplasia
NONOPERATIVE MANAGEMENT
Nonoperative management of pediatric trigger thumb has been described, including simple observation,1 daily stretching by parents,25 splinting,11,16 and casting.4
Watanabe and colleagues25 reported the results in 58 patients of passive stretching performed by the patient's mother 10 to 20 times daily for an average of 44 months. Despite claiming a 96% “satisfactory result,” the authors describe only 25% of patients with locked flexion deformities experiencing improvement, and none recovering normal interphalangeal joint hyperextension. Thus, it is unclear whether their results differ from other reports of natural history, even after years of stretching exercises.
Lee and associates11 reported their results of splinting for passively correctable trigger thumbs (no locked flexion or extension deformities), finding a greater chance of improvement (decreased frequency of triggering) with splinting than with simple observation. Others16 have reported improvement in triggering with nighttime splint treatment averaging 10 months, but in a series that included trigger fingers, there was a 24% drop-out rate and there was no control group.
The role of conservative treatment of pediatric trigger thumb remains controversial. It is unclear whether conservative treatment affects the natural history and whether conservative treatment is useful for children who present with a fixed flexion posture at the interphalangeal joint (most cases).
Nonetheless, it is clear from the available data that conservative treatment offers a chance of improvement only after many months to years of daily exercises or splint use, and recovery of truly normal interphalangeal joint motion is uncommon.
Percutaneous needle release of the A1 pulley as an office procedure under local anesthesia has been described for pediatric trigger thumb, but with lower success rates than open surgical release; reported complications include incomplete release and patient intolerance of the procedure.24
SURGICAL MANAGEMENT
Surgical release of the A1 pulley has long been recognized as a safe and effective treatment for pediatric trigger thumb.
When forming surgical indications, the surgeon must consider the available data regarding the natural history and the outcomes of conservative treatment outlined above and must discuss the options with the family. Nearly all reports of surgical treatment of trigger thumb describe complete resolution of the condition in the immediate postoperative period with a low complication rate, making surgical treatment an attractive option.
The timing of surgery is controversial. Most authors recommend delaying surgery until 1 year of age; some recommend delaying surgery until after 3 or even 5 years of age; and others just recommend an undefined period of observation before surgery. No study has shown a clear detrimental effect of delaying surgery until 3 years or later, although compensatory metacarpophalangeal joint hyperextension laxity, permanent capsular contracture of the interphalangeal joint, and coronal plane deformity of the thumb have been cited as reasons to operate before 3 years of age.
Preoperative Planning
Little preoperative planning is required other than preparing the child medically for the surgery and anesthesia and preparing the family for the surgery and early postoperative recovery period.
Positioning
The patient is positioned supine on the operating table with the affected arm (or arms) extended on a hand table or armboard.
A pneumatic tourniquet is placed about the upper arm. The entire limb distal to the tourniquet is prepared and draped.
The limb is exsanguinated with an Esmarch bandage and the tourniquet is inflated to 200 mm Hg.
Approach
The approach to the A1 pulley is best performed through a transverse incision in or immediately parallel to the palmar digital crease. Longitudinal incisions can cause loss of metacarpophalangeal joint mobility by scar contracture long term.13
As mentioned previously, great care must be taken in the volar approach to prevent injury to the digital nerves that lie in proximity to the A1 pulley.
TECHNIQUES
EXPOSURE
A 7-to 10-mm transverse incision is planned in the region of the palmar digital crease. The exact location of the incision depends on the location of the A1 pulley relative to the crease. In the thumb with a fixed flexion posture, the proximal edge of the A1 pulley is immediately distal to the location of the palpable nodule when the interphalangeal joint is maximally extended.
The incision need not be in the interphalangeal crease to heal with an almost imperceptible scar.
Care must be taken to plan the incision directly over the thumb flexor sheath, which is pronated relative to the plane of the palm (TECH FIG 1A).
The incision is made after exsanguination and tourniquet inflation. Great care must be taken to avoid incising the immediately adjacent digital nerves.
The subcutaneous tissue is then spread bluntly to reveal the A1 pulley. The digital nerves need not be routinely dissected, as long as the transverse fibers of the pulley are very clearly visualized under loupe magnification (TECH FIG 1B).
TECH FIG 1 • A. Incision location for open release of pediatric trigger thumb. B. Exposure of the A1 pulley. Note the transversely oriented fibers without overlying subcutaneous tissue. The retractors on each side can be adjusted proximally and distally to allow visualization of the entire A1 pulley.
OPEN RELEASE OF THE A1 PULLEY
The distal and proximal edges of the A1 pulley are identified and the A1 pulley is sharply incised longitudinally along its entire length (TECH FIG 2A). The oblique pulley is identified and protected distally. A gentle spread with a blunt scissor or hemostat in the proximal aspect of the sheath entering the thenar eminence will disrupt any remaining fibrous bands that can be a source of recurrent triggering.
The initial incision in the A1 pulley will produce an elliptical window in the pulley that may allow full extension of the interphalangeal joint (TECH FIG 2B), but the digit will still trigger postoperatively unless the entire pulley is divided.
After adequate release, the distal edge of the A1 pulley should be separated by several millimeters, with the entire width of the flexor pollicis longus tendon clearly visible (TECH FIG 2C).
After adequate release, the thumb interphalangeal joint should have full range of motion (TECH FIG 2D). In longstanding cases, that range of motion may not be much beyond neutral.
If the thumb was locked in an extended position before tendon release, complete release can be confirmed by fully extending the wrist and compressing the distal volar forearm to provide proximal traction on the flexor pollicis longus tendon.
If the thumb does not have full flexion of the interphalangeal joint with these maneuvers, the release is incomplete.
TECH FIG 2 • A. Longitudinal division of the A1 pulley with a 6700 Beaver blade under direct visualization. B. Appearance of the A1 pulley after incomplete release. Note the elliptical cut edges of the pulley and the full extension of the interphalangeal joint. The intact proximal and distal ends of the pulley will be sources of recurrent triggering unless the entire pulley is released. C. Complete release of the A1 pulley. The flexor pollicis longus tendon is visible across its entire width. The forceps are holding one cut edge of the pulley. D. Full passive extension of the interphalangeal joint immediately after A1 pulley release of the patient in Figure 1A.
CLOSURE AND DRESSING
The wound is irrigated and closed with simple absorbable sutures.
The wound is infiltrated with long-acting local anesthetic without epinephrine for postoperative analgesia.
The wound is covered by a sterile dressing and several layers of bandage and tape to prevent the child from removing the bandage (TECH FIG 3).
TECH FIG 3 • Postoperative dressing for trigger thumb release. Loosely wrapped gauze (A) is covered by a loosely wrapped elastic bandage (B) and a doubled-back stockinette (C) with ample tape. The multiple layers prevent premature removal by the patient. Great care must be taken to keep the dressing loose to prevent excessive swelling or even ischemia distally.
POSTOPERATIVE CARE
Cast or splint immobilization is not necessary postoperatively. However, protecting the incision for 7 days allows less inflamed wound healing and gives the absorbable sutures time to dissolve before the inquisitive toddler is allowed access to them.
A multilayer dressing of gauze, tape, elastic bandage, tape, stockinette, and tape is reliable and well tolerated.
Dressings are removed at 7 days. If a determined child manages to escape the dressing prematurely, an adhesive bandage is used in its place until postoperative day 7.
No activity restrictions are imposed postoperatively, other than routine wound care.
Postoperative analgesic medication beyond a single appropriate dose of acetaminophen is typically unnecessary.
Outpatient postoperative follow-up is scheduled for 1 to 2 weeks after the surgery. Full active range of motion and function of the thumb are typically achieved within 1 to 2 weeks of dressing removal. If parents perceive hesitance to use the thumb beyond that time period, a brief course of pediatric occupational therapy may be helpful.
OUTCOMES
Outcomes of open surgical release of triggers thumbs are excellent. Recovery of full range of motion is reported in all patients in many series.6–8,18,20,26
Series that report less than 100% surgical cure describe recurrence due to incomplete pulley release as the most common reason for unsatisfactory outcome.9,12 In these series, however, success rates exceed 93%, with 100% success after reoperation of the cases with incomplete release.
Recovery of full range of motion after surgical correction is generally immediate. In longstanding cases, full hyperextension of the interphalangeal joint may take months to achieve despite achieving neutral extension immediately postoperatively. This phenomenon may represent a volar plate or capsular contracture of the interphalangeal joint from a prolonged locked flexion posture.
A recent study of the long-term results of surgical treatment shows that despite obtaining normal motion postoperatively, 23% of patients followed an average of 15 years postoperatively have mild loss of interphalangeal joint motion.13
COMPLICATIONS
Although rare, recurrence of the flexion posturing or triggering is the most commonly reported complication; it is attributed to incomplete pulley release.9,12,22 Careful attention to surgical technique prevents this complication. If recurrence occurs, revision of the surgery with complete pulley release is curative.
Longitudinal incisions are associated with scar contracture and patient complaints long term.13
Digital nerve injuries are exceedingly rare and unreported in all series reviewed here.
Superficial wound infection has been reported21 but is generally easily treated with oral antibiotics.
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