Release of the A1 Pulley to Correct Pediatric Trigger Thumb

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.14, 19, 22, 24

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 precise knowledge of the anatomy is important.

PATHOGENESIS

The pathogenesis of pediatric trigger thumb is unknown, although recent evidence implicates benign proliferation of myofibroblasts during growth.13

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.28

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, 20

A 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 may 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 preexisting 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 long-standing cases of fixed flexion deformity, thumb metacarpophalangeal joint hyperextension laxity is common.

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In other cases, a coronal plane deformity resembling clinodactyly may be present, although a causative relationship has yet to be established.

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, whereas the metacarpophalangeal joint is fixed in flexion, differentiating congenital clasped thumb from pediatric trigger thumb.

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 because the thumb-in-palm deformity of cerebral palsy can be confused with 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.

Radiographs may be misinterpreted as demonstrating a dorsal dislocation of the metacarpophalangeal joint due to its hyperextended posture, leading to attempts to “reduce” the dislocation. Often, these misguided attempts to reduce the dislocation involve traction on the thumb, which may pull the nodule through the pulley by extending the interphalangeal joint, satisfying the practitioner and parent that the problem has been solved. The flexed posture usually returns by the following morning, leading to a diagnosis of recurrent dislocation.

Familiarity with the diagnosis of trigger thumb and its radiographic and clinical findings can prevent this cycle of intervention and anxiety.

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,30 splinting,16, 21 and casting,4 but it is unclear if any nonoperative treatment alters the natural history.

A recent systematic review7 summarized the results of conservative treatment of pediatric trigger thumbs as follows. Splinting was reported in 138 thumbs in 4 studies15, 16, 21, 26 with an overall success rate of 67% over

2.9 to 30 months, although the splinting was complicated by poor compliance and splint complications such as

contact dermatitis. Many patients treated with splinting dropped out of the treatment to proceed with surgery. Passive stretching of the thumb was reported in 108 thumbs in 3 series,8, 12, 30 with an overall success rate of 55% after 21 to 24 months of daily exercising. In addition, the success was even lower for thumbs locked in

flexion. Therefore, the author discourages the use of nonoperative treatment, as it does not appear to alter the

natural history despite long, arduous treatment regimens.

In a series representative of splint treatment, Lee and associates16 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. Others21 have reported improvement in triggering with nighttime splint treatment averaging 10 months, but in a series that included trigger fingers, there was a 24% dropout rate and there was no control group.

In a series representative of passive stretching, Watanabe and colleagues30 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.

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.29

SURGICAL MANAGEMENT

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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 earlier 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 interphalan-geal joint, and coronal plane deformity of the thumb have been cited as reasons to operate before 3 years of age. Anesthesia risk, although not completely elucidated in relation to age, should be considered in the decision regarding timing as well.

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 arm board.

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 100 mm Hg over systolic pressure.

Alternatively, the Esmarch bandage can be used as a tourniquet about the forearm after exsanguinating the hand and wrist, although experience with this technique is necessary to avoid injury to the forearm from excessive pressure.

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.18

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 skin 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).

   

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  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 FIG 1A.

   

   

  After adequate release, the thumb interphalangeal joint should have full range of motion (TECH FIG 2D). In long-standing 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.

• 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.

TECH FIG 3 • Postoperative dressing for trigger thumb release. Loosely wrapped gauze is covered by a loosely wrapped cohesive bandage. Great care must be taken to keep the dressing loose to prevent excessive swelling or even ischemia distally.

The wound is covered by a sterile dressing and cohesive bandage to prevent the child from removing the bandage (TECH FIG 3).

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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 and cohesive bandage is reliable and well tolerated.

Great care must be taken to prevent overtightening any elastic bandage and causing vascular compression.

Dressings are removed in 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, although children older than 8 to 10 years of age at the time of surgery tend to require more analgesics.

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 trigger thumbs are excellent.

Recovery of full range of motion is reported in all patients in many series.6, 9, 10, 23, 25, 31

A recent systematic review found a 95% success rate in 759 thumbs in 12 series.7

Series that report less than 100% surgical cure describe recurrence due to incomplete pulley release as the most common reason for unsatisfactory outcome.11, 17 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 long-standing 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 at an average of 15 years postoperatively have mild loss of interphalangeal joint motion.18

COMPLICATIONS

Although rare, recurrence of the flexion posturing or triggering is attributed to incomplete pulley release.11, 17, 27 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.18 Wound complication was the most common reported complication in a systematic review of trigger thumb

surgery,7 although specific details regarding these complications were not described.

Digital nerve injuries are exceedingly rare, being reported in only 1 of 759 thumbs reviewed in a recent systematic review.7

Superficial wound infection has been reported26 but is generally easily treated with oral antibiotics.

REFERENCES

1. Baek GH, Kim JH, Chung MS, et al. The natural history of pediatric trigger thumb. J Bone Joint Surg Am 2008;90:980-985.

    

    

2. Bayat A, Shaaban H, Giakas G, et al. The pulley system of the thumb: anatomic and biomechanical study. J Hand Surg Am 2002;27: 628-635.

    

    

3. Buchman MT, Gibson TW, McCallum D, et al. Transmission electron microscopic pathoanatomy of congenital trigger thumb. J Pediatr Orthop 1999;19:411-412.

    

    

4. Conners JJ, Obi LJ. Conservative treatment of trigger thumb in infants and children. J Fla Med Assoc 1968;55:819.

    

   P.670

    

5. Dunsmuir RA, Sherlock DA. The outcome of treatment of trigger thumb in children. J Bone Joint Surg Br 2000;82:736-738.

    

    

6. Eyres KS, McLaren MI. Trigger thumb in children: results of surgical correction. J R Coll Surg Edinb 1991;36:197-198.

    

    

7. Farr S, Grill F, Ganger R, Girsch W. Open surgery versus nonoperative treatments for paediatric trigger thumb: a systematic review. J Hand Surg Eur Vol 2014;39(7):719-726.

    

    

8. Forlin E, Kaetsu EY, Vasconcelos JEE. Success of conservative treatment of trigger thumb in children after minimum follow-up of five years. Rev Bras Ortop 2012;47:483-487.

    

    

9. Ger E, Kupcha P, Ger D. The management of trigger thumb in children. J Hand Surg Am 1991;16:944-947.

    

    

10. Herdem M, Bayram H, Togrul E, et al. Clinical analysis of the trigger thumb of childhood. Turk J Pediatr 2003;45:237-239.

     

     

11. Hudson DA, Grobbelaar AO, Bloch CE. Trigger thumb in children— results of simple surgical treatment. S Afr J Surg 1998;36:91-92.

     

     

12. Jung HJ, Lee JS, Song KS, et al. Conservative treatment of pediatric trigger thumb: follow-up for over 4 years. J Hand Surg Eur Vol 2012; 37:220-224.

     

     

13. Khoshhal KI, Jarvis JG, Uhthoff HK. Congenital trigger thumb in children: electron microscopy and immunohistochemical analysis of the first annular pulley. J Pediatr Orthop B 2012;21:295-299.

     

     

14. Kikuchi N, Ogino T. Incidence and development of trigger thumb in children. J Hand Surg Am 2006;31:541-543.

     

     

15. Koh S, Horii E, Hattori T, et al. Pediatric trigger thumb with locked interphalangeal joint: can observation or splinting be a treatment option? J Pediatr Orthop 2012;32:724-726.

     

     

16. Lee ZL, Chang CH, Yang WY, et al. Extension splint for trigger thumb in children. J Pediatr Orthop 2006;26:785-787.

     

     

17. Marriott FP. Trigger thumb in infancy and childhood. A survey of 80 patients. Ulster Med J 1967;36:53-61.

     

     

18. McAdams TR, Moneim MS, Omer GE Jr. Long-term follow-up of surgical release of the A(1) pulley in childhood trigger thumb. J Pediatr Orthop 2002;22:41-43.

     

     

19. Moon WN, Suh SW, Kim IC. Trigger digits in children. J Hand Surg Br 2001;26:11-12.

     

     

20. Mulpruek P, Prichasuk S. Spontaneous recovery of trigger thumbs in children. J Hand Surg Br 1998;23:255-257.

     

     

21. Nemoto K, Nemoto T, Terada N, et al. Splint therapy for trigger thumb and finger in children. J Hand Surg Br 1996;21:416-418.

     

     

22. Rodgers WB, Waters PM. Incidence of trigger digits in newborns. J Hand Surg Am 1994;19:364-368.

     

     

23. Skov O, Bach A, Hammer A. Trigger thumbs in children: a follow-up study of 37 children below 15 years of age. J Hand Surg Br 1990;15:466-467.

     

     

24. Slakey JB, Hennrikus WL. Acquired thumb flexion contracture in children: congenital trigger thumb. J Bone Joint Surg Br 1996;78:481-483.

     

     

25. Sprecher EE. Trigger thumb in infants. Clin Orthop 1953;1:124-128.

     

     

26. Tan AH, Lam KS, Lee EH. The treatment outcome of trigger thumb in children. J Pediatr Orthop B 2002;11:256-259.

     

     

27. Taylor BA, Waters PM. A case of recurrent trigger thumb. Am J Orthop 2000;29:297-298.

     

     

28. Vyas BK, Sarwahi V. Bilateral congenital trigger thumb: role of heredity. Indian J Pediatr 1999;66:949-951.

     

     

29. Wang HC, Lin GT. Retrospective study of open versus percutaneous surgery for trigger thumb in children. Plast Reconstr Surg 2005;115:1963-1970.

     

     

30. Watanabe H, Hamada Y, Toshima T, et al. Conservative treatment for trigger thumb in children. Arch Orthop Trauma Surg 2001;121: 388-390.

     

     

31. White JW, Jensen WE. Trigger thumb in infants. AMA Am J Dis Child 1953;85:141-145.