Trigger Thumb

Etiology

The exact cause of trigger thumb remains unknown, but several predisposing factors have been identified. Overuse of the hands, repetitive gripping maneuvers, and conditions promoting diffuse tenosynovial growth are associated with an increased risk. Individuals with diabetes, amyloidosis, hypothyroidism, gout, and rheumatoid arthritis face an elevated risk of developing trigger thumb.[5][6][7][8] Despite reports linking certain occupations involving extensive gripping and hand flexion to trigger digits, studies have not consistently established a direct relationship between occupation and trigger thumb. The condition's etiology is considered multifactorial.

The probable cause of trigger thumb is a size disparity between the A1 pulley and the FPL tendon. In children, this could result from tendon swelling or pulley thickening. Suggested etiologies include trauma, diabetes, mucopolysaccharidosis, and anatomical abnormalities.

In adults, the size disparity is likely due to hypertrophy caused by elevated pressures at the A1 pulley's edge. Maximum flexion and tight grips exert the highest pressures, leading to hypertrophy and fibrocartilaginous metaplasia at the tendon-pulley interface. Thickening of the tendon sheath and the tendon restricts movement, causing the tendon to swell and thicken, forming a Notta's nodule.[9][10][11] Once the nodule attains a substantial size, triggering occurs. Although the flexors can overcome this resistance, the weaker extensors may struggle, causing the thumb to become stuck in flexion. Salloum et al have reported that trauma may accelerate trigger thumb development in predisposed individuals, although it is unlikely to be a causative factor in the initial development.[12]

Epidemiology

Over 200,000 individuals in the United States are affected by trigger fingers and thumbs annually, making it a common concern. This condition is most prevalent in females aged 40 to 60. The lifetime risk of developing a trigger finger is 2% to 3%, but this risk rises to 10% for individuals with diabetes.

Although the occurrence of congenital trigger thumb is rare, pediatric trigger thumb is also relatively uncommon, with an incidence of approximately 3.3 cases per 1000 live births at the age of 1.[4][10] Notably, this condition is bilateral in 25% to 30% of patients, underscoring the importance of a comprehensive examination of both sides.[13]

Pathophysiology

Thickening of the A1 pulley causes a size mismatch between the FPL and the inner diameter of the A1 pulley. This thickening is clinically evident through the formation of a Notta's nodule, resulting from FPL tendon fibers spiraling and bunching up as they pass through the thickened pulley. When the Notta's nodule reaches a significant size, the FPL tendon gets stuck at the A1 pulley during extension. In some cases, difficulty with flexion may arise if the distal end of the A1 pulley is affected.[14] 

Histopathology

The histopathological feature of trigger digits, including a trigger thumb, involves fibrocartilaginous metaplasia of the ligamentous layer of the flexor tendon sheath at the A1 pulley. Electron microscopy reveals fibroblasts and abundant mature collagen, with no apparent inflammatory or degenerative changes in the A1 pulley.[14][15]

History and Physical

The presentation of a trigger thumb varies, ranging from mild to moderate symptoms. Early signs include soreness at the base of the thumb close to the MCP joint. Progression of symptoms involves pain and stiffness during thumb flexion, along with swelling or a tender lump on the palmar side of the metacarpal head. Advanced cases may exhibit locking of the thumb in a flexed position, making it challenging to extend fully. Patients may require assistance to straighten the thumb, experiencing popping or snapping upon release from the locked position. 

The most common presentation in pediatric patients with trigger thumb is a thumb locked in flexion.[16] Passive extension of the thumb is often possible and is normal. Actual triggering may be uncommon, and occasionally, the presentation is that of the thumb locked in extension.[17]

During examination, adult patients exhibit tenderness at the MCP joint and may resist allowing the examiner to extend the digit. Extension reveals a distinctive popping sensation with an observed snap into extension. The classification of a trigger thumb can be based on the Quinnell or Sugimoto grading systems. 

Quinnell Grading System for Flexion and Extension

• 0: Normal movement
• I: Uneven movement
• II: Actively correctable locking of the digit
• III: Passively correctable locking of the digit
• IV: Fixed deformity [18]

Sugimoto Classification System

• Stage I: Normal with a palpable nodule
• Stage II: Active triggering
• Stage III: Passive movement elicits triggering
• Stage IV: Thumb locked in flexion [19]

As pediatric trigger thumb can result in hyperextension at the MCP joint, it can be classified based on the presence or absence of MCP hyperextension, as mentioned below.

• Type I: This type of trigger thumb is associated with MCP hyperextension.
• Type II: This type of trigger thumb does not have MCP hyperextension.[20]

Evaluation

Trigger thumb is a clinical diagnosis based on history and physical examination. During the examination, the patient's hands are placed with the palms up in a relaxed position, and the patient is asked to slowly and actively flex and extend the thumb to detect any locking or catching. The clinician can facilitate this by flexing the patient's other digits. If active triggering is not observed, the examiner places fingers on the MCP joint as the thumb is actively flexed and extended, noting any clicking sensation or loss of smooth motion. Locking may not occur with each motion. Imaging is not necessary for the diagnosis of trigger thumb.

In a prospective study utilizing serial ultrasonographic assessment of pediatric trigger thumb, triggering is observed when the cross-sectional area of the FPL tendon exceeds that at the A1 pulley. The condition resolves when this size disparity is corrected. Patients with unilateral triggering and a trigger ratio (the ratio of the cross-sectional area of the involved FPL to uninvolved FPL) less than 1.5 are susceptible to developing the condition bilaterally.[11] 

In another cross-sectional trial utilizing ultrasonographic measurements in trigger thumb, the analysis of the cross-sectional area of the FPL tendon at the MCP (C1) and the cross-sectional area of the FPL tendon at the midpoint of the first metacarpal (C2) revealed that the C1/C2 ratio in a healthy thumb is relatively stable, with a mean value of 0.983 ± 0.103. The cutoff value for C1/C2 to diagnose trigger thumb is 1.362 in children and 1.153 in adults.[21] Chang et al describe MRI findings in patients with trigger thumb that include FPL tendinosis with a distinct nodule, A1 pulley thickening, and tenosynovitis; also present are abnormal Av pulleys in some cases.[22]

Treatment / Management

Clinicians tailor the treatment for trigger thumb based on symptom severity and duration, initiating conservative management and pain relief measures. Nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen or naproxen are commonly used for pain relief. The various conservative therapy approaches include: 

• Taking rest for 3 to 4 weeks.

• Avoiding activities that involve repetitive gripping, repeated grasping, or prolonged use of vibrating hand-held machinery.

• Applying ice to the palm several times daily, which may help alleviate symptoms for some patients.

• Taking warm-water soaks, particularly in the morning.

• Using nighttime splinting to keep the affected finger in an extended position.

• Incorporating gentle passive thumb movements to maintain mobility.[23][24][25]
(A1)

The initial approach to treating pediatric trigger thumb involves conservative management, incorporating thumb splinting, observation, and passive extension exercises. Clinicians typically recommend a trial of nonoperative treatment lasting at least 6 months.[26] In a prospective study examining the natural history of pediatric trigger thumb in the United States, nearly one-third of patients experienced spontaneous resolution.[16]

Healthcare professionals may recommend a minor invasive or surgical procedure after failed conservative management. The predominant treatment for adult trigger thumb involves corticosteroid injections, typically with methylprednisolone or triamcinolone, directly into the tendon sheath. Corticosteroids alleviate inflammation, promoting smooth tendon movement within the sheath. This approach yields improvement in 90% of patients, but it is not recommended for children with congenital trigger thumb.

Patients with diabetes must diligently monitor blood sugar levels due to potential steroid-induced hyperglycemia following injections. While a second injection is an option, caution is warranted as repeated injections may cause tendon damage. Recent meta-analyses of randomized controlled trials affirm superior outcomes with corticosteroid injections compared to control injections in managing trigger digits.[27] However, corticosteroid injections for trigger thumb pose a risk of FPL tendon rupture. To mitigate this complication, patients should observe the following steps:(A1)

• Administering the drug carefully into the tendon sheath and avoiding intratendinous injection.

• Ensuring the triamcinolone dose remains less than 10 mg.

• Limiting injections to a maximum of 2 times.

• Maintaining a minimum 3-month interval between successive injections.[28] 
(B3)

A percutaneous release of the A1 pulley is a potential intervention for nonresponsive cases. A digital block with a local anesthetic is performed, and the pulley is blindly released using a needle. The primary risk is damage to the radial digital nerve, which crosses obliquely at the MCP joint. Open surgical intervention is considered the gold standard for patients who have not benefited from other treatment modalities. Trigger thumb surgery is an ambulatory procedure performed through an incision over the MCP joint. The A1 pulley is released to enable free movement of the FPL tendon. Early thumb movement is encouraged to minimize scar tissue formation and reduce the risk of recurrence. Follow-up appointments in the outpatient clinic are essential to assess function and monitor improvement.[29](B3)

Children with congenital trigger thumb should undergo surgical release of the A1 pulley if conservative management fails. For individuals who begin presenting symptoms after the age of 2, surgical intervention is often recommended as a primary approach due to the lower success rate of conservative methods in this population.[4] Early surgical intervention is advisable for patients with stage IV trigger thumb who can safely undergo anesthesia, with surgery being prioritized over observation or splinting.[30] 

Dittmer et al recommend immediate surgery for patients with stage IV disease, without an observational period. They propose conservative management and at least 1 year of safe observation before considering surgery for patients with stage II and stage III disease.[19] Other studies suggest that patients with thumb interphalangeal joint flexion contractures exceeding 30° at presentation may not experience spontaneous resolution within 3 years, making early surgical intervention a preferable management strategy.[16] 

Administering local anesthetic before incision for an open A1 pulley release in trigger thumb reduces the requirement of the general anesthetic sevoflurane when performing the procedure under general anesthesia.[31] In a randomized trial comparing various techniques of open A1 pulley release, disconnecting the A1 pulley at the extreme radial side accelerates postoperative pain relief and functional recovery.[32] However, undergoing three or more preoperative corticosteroid injections and receiving a corticosteroid injection within 3 months before surgery increases the risk of postoperative complications in trigger thumb.[33](A1)

In a retrospective study, modified acupotomy, a percutaneous A1 pulley release procedure practiced in China, was compared to percutaneous release for trigger thumb. The findings revealed that the modified acupotomy procedure offers superior long-term outcomes and satisfaction compared to percutaneous release. However, in the short term, percutaneous release resulted in less residual pain and higher satisfaction.[34] (B2)

Differential Diagnosis

The differential diagnoses of trigger thumb include clasped thumb deformity, spasticity, absence or aberrance of the extensor mechanism, arthrogryposis, congenital stiffness of the distal interphalangeal joint of the thumb, hyperflexible thumb,[26] de-Quervain tenosynovitis,[35] Dupuytren contracture, diabetic cheiroarthropathy, calcific peritendinitis or periarthritis, infectious tenosynovitis, MCP sprain, and noninfectious tenosynovitis.

Infectious tenosynovitis presents with severe pain, decreased range of motion, warmth, erythema, and tenderness to palpation over the flexor tendon sheath. Assessment should explore minor trauma, such as lacerations or punctures involving the thumb or hand. Early recognition is crucial, as closed-space infection can lead to tendon rupture, restricting thumb motion. Noninfectious tenosynovitis similarly presents with pain, tenderness, and swelling along the flexor tendon.

Underlying inflammatory arthritis, such as rheumatoid or reactive arthritis, is commonly associated with noninfectious tenosynovitis. In contrast to trigger digits, noninfectious tenosynovitis manifests with swelling and pain along the long axis of the affected tendon and joints. Treatment involving NSAIDs, disease-modifying antirheumatic drugs (DMARDs), and systemic glucocorticoids significantly alleviates symptoms.

An MCP sprain is typically a result of trauma, and patients may report tenderness on either side of the MCP joint along with a reduction in full flexion. However, unlike trigger thumb, there is no associated clicking sensation.

Patients with diabetic cheiroarthropathy typically present with an inability to flex or extend the MCP and interphalangeal joints. The involvement is usually symmetrical, affecting all fingers, and the condition is generally painless. The dorsum of the hand may exhibit a tight and waxy appearance.

Patients with Dupuytren contracture experience a loss of full extension at the MCP joint of the affected finger or fingers. Unlike trigger digits, the loss of extension is chronic and fixed. Dupuytren contracture is typically painless, and nodular lesions are often present in the palmar fascia. A fibrous cord develops, extending from the palm to the digits.

Prognosis

The overall prognosis for trigger thumb is generally favorable. Spontaneous resolution is possible in pediatric patients, while conservative management successfully treats most adult patients and those younger than 2. Approximately 45% of patients experience symptom relief for at least 10 years following a glucocorticoid injection. Surgical release of the A1 pulley is required for those unresponsive to conservative measures with favorable outcomes.[36] The recurrence rate after surgical intervention for trigger thumbs is reported as 1.4%.[13]

Complications

Complications related to corticosteroid injection include infection, tendon rupture, and symptom recurrence.[28] 

Surgical complications include insufficient release, tendon laceration, bowstringing, infection, stiffness, weakness, digital artery pseudoaneurysm, digital nerve injury, and recurrence.[28]