Trigger Finger

Etiology

The etiology of trigger finger is multifaceted and can be associated with specific comorbid diseases, such as diabetes, amyloidosis, carpal tunnel syndrome, gout, thyroid disease, and rheumatoid arthritis, in adults. Traumatic forces lead to hypertrophy and inflammation of the tendon and its sheath, resulting in catching and locking sensations due to the inability to slide smoothly within its sheath. Certain local anatomical anomalies, such as the insertion of a lumbrical into the A1 pulley, can also cause trigger finger.[4]

In children, the etiology of the condition is believed to be developmental, arising from a mismatch in size between the flexor tendon of the thumb and its tendon sheath. Fibroblast proliferation leads to a discrepancy in the size between the tendon and the A1 pulley sheath. Although most cases are idiopathic during childhood, they may also be associated with congenital metabolic (eg, Hurler syndrome) and inflammatory conditions (eg, juvenile rheumatoid arthritis).[5][6]

Epidemiology

Trigger finger exhibits a bimodal incidence, with the first peak occurring before the age of 8 in children and the second peak between the ages of 40 and 50 in adults. Overall, trigger finger is more common in adults. In children, both boys and girls are equally likely to experience this condition, which usually affects the thumb. In adults, trigger finger is more likely to affect women, typically in their dominant hand.[3]

Pathophysiology

Microtrauma resulting from repetitive use or compression forces induces inflammation and injury to the flexor tendon-sheath complex. The most commonly affected site, the A1 pulley, bears the most significant force. Prolonged inflammation leads to the tendon adhering within its sheath, producing a "locking" sensation for the patient. Due to the superior strength of the flexor tendon apparatus compared to the extensor tendon apparatus, patients typically do not encounter difficulty when flexing their fingers. However, inflammation causes the flexor tendon to catch in the flexor sheath during extension, leading to noticeable locking when attempting to extend the fingers.[7]

Histopathology

Although the diagnosis of trigger finger is primarily clinical, histopathological findings reveal fibro-cartilaginous metaplasia at the tendon-pulley interface, accompanied by hypertrophy and inflammation. A histological and immunohistochemical study of excised tissue specimens from patients with trigger fingers identified amyloid deposits in the annular ligament. Two distinct types of amyloids—ATTR and AFib—that affect the annular ligament were observed. Each type exhibits unique demographic characteristics and histomorphological deposition patterns.[8]

History and Physical

Patients with trigger finger typically present with either discomfort or functional limitations in the affected digit. Patients may report stiffness, discomfort, or progressive pain on the palmar aspect of the affected digit during flexion, which is accompanied by a frequent complaint of a painful click in the digit. Patients may also present with locking of the finger during extension or an inability to move a finger from a fixed flexed position. In addition, patients often complain that the condition interferes with their work. Symptoms may develop gradually or manifest acutely. 

During the physical examination of a patient with trigger finger, a tender nodule or swelling at the distal palmar crease may be observed. The affected digit might be flexed and locked, and attempts to move it can cause pain and/or snapping.[9]

Evaluation

The diagnosis of the trigger finger is clinical, and is presumed in patients whose finger locks during flexion, clicks painfully, and catches upon extension. An inflamed nodule at the base of the affected finger further supports the diagnosis.[10][11]

Ultrasound is the preferred imaging modality for evaluating this condition. Ultrasound enables both static and dynamic evaluation of trigger finger, facilitating comparison with adjacent normal digits.[12] Although this imaging technique may demonstrate thickening of the pulley, as well as inflammation and irregularity of the underlying flexor tendon, it may not reliably predict the site. Ultrasound can also be used dynamically to demonstrate the catching and clicking phenomena during tendon sliding.

Plain radiographs can rule out other conditions, such as occult fractures, thereby making magnetic resonance imaging (MRI) and computed tomography (CT) scans typically unnecessary for diagnosing trigger finger.

Treatment / Management

Trigger finger can be managed in 2 ways—either by nonsurgical approaches, which involve steroid injection and splinting, or surgical interventions.

Nonsurgical Procedures

The primary approach to treating trigger finger typically involves nonoperative methods, particularly when the condition is uncomplicated and symptoms have recently manifested. Nonoperative treatments include steroid injections and splinting.

Steroid injections: Administering steroids into the tendon sheath is frequently an effective initial treatment approach for patients with trigger finger. This method is cost-effective, easily executed, and less invasive than surgery. While many patients may find relief with a steroid injection, there is a potential for symptom recurrence. Adverse effects of steroid injections may include tissue atrophy, skin discoloration, hypopigmentation, or infection. Prolonged symptoms are associated with a lower likelihood of resolution.

Steroid injections can be administered blindly using clinical landmarks or with the assistance of ultrasound guidance. A prospective randomized study compared the clinical outcomes of ultrasound-guided and blinded corticosteroid injections for trigger finger. The findings indicated that using ultrasound guidance for corticosteroid injections was more effective in treating trigger fingers compared to the blinded method. This technique resulted in superior outcomes and a faster return to work during the early stages of treatment.[13]

Splinting: Splinting is intended to limit tendon gliding and reduce inflammation. Utilizing a metacarpophalangeal (MCP) blocking splint set at 10° to 15° of flexion for a duration of 6 to 10 weeks is a common approach. However, its effectiveness is diminished for patients with severe or prolonged symptoms.

A randomized study was conducted to assess pain relief and functional improvement in patients with trigger finger by evaluating the effectiveness of 3 different treatment options—steroid injection alone, splinting alone, or a combination of both procedures. The study found no significant difference in pain relief or functional outcomes at 1 year among these 3 treatment options. As a result, it is recommended to consider splinting alone as the initial treatment for patients with trigger finger.[14]

Surgical Procedures

The gold standard for surgically managing trigger finger is the open release of the A1 pulley. Surgical intervention should be considered under the following circumstances:

• Lack of improvement with splinting and injection treatment

• Irreducibly locked trigger finger

• Trigger thumb during infancy: Infants will likely develop a fixed flexion deformity of the interphalangeal joint without surgical release. Given that the causes of trigger finger in children extend beyond a thickened A1 pulley, the outcomes of conservative treatment are unpredictable.

Percutaneous release of the A1 pulley is an alternative management strategy, necessitating a precise understanding and recognition of specified landmarks. Despite the efficacy and safety of the percutaneous technique for the thumb, many physicians recommend against its use on the thumb due to the presence of the digital nerve coursing over the A1 pulley. Potential concerns with this approach include incomplete pulley release and the risk of damage to the flexor tendons and digital nerves. According to a retrospective study, the overall success rate for percutaneous A1 pulley release for trigger fingers is 87%. Notably, the involvement of the index finger, middle finger, or ring finger is associated with a higher failure rate of percutaneous release.[15]

According to a prospective randomized study, the outcomes of open release were found to be comparable to those of ultrasound-guided percutaneous small needle knife release for trigger digits.[16] For advanced or recurrent trigger fingers, the division of one or more slips of the flexor digitorum superficialis (FDS) tendon is reported as an effective surgical modality. This approach is especially recommended for patients with diabetes or rheumatoid arthritis, as well as those with fixed flexion deformities that may result in poor functional outcomes from A1 pulley release alone. A recent systematic review indicated that FDS resection is an effective and safe procedure with low recurrence rates for long-standing trigger fingers.[17](A1)

In a 12-year retrospective observational study aimed at identifying factors associated with recurrence after open surgical release in adult trigger fingers, it was discovered that receiving more than 3 steroid injections before surgery and engaging in manual labor increased the risk of recurrence following an open A1 pulley release.[18] In addition, it is advised to avoid administering a fourth steroid injection. 

For patients with advanced trigger finger, characterized by limitations in active or passive range of digit movements, achieving a full range of motion may necessitate reduction flexor tenoplasty and partial or complete resection of the FDS tendon. Subsequent hand physiotherapy and splinting may be recommended to optimize outcomes.[19] 

Differential Diagnosis

Some potential differential diagnoses for patients presenting with this condition include abnormal sesamoids, acromegaly, ganglion cyst of the wrist, ganglion involving the tendon sheath, infection within the tendon sheaths, presence of loose body in MCP joint, subluxation of extensor digitorum communis, osteophytes on the metacarpal head, palmar plate dislocation, and boxer's knuckle.[20]

Prognosis

The prognosis is favorable with appropriate treatment. Although most patients respond well to corticosteroid injections, some cases may resolve spontaneously when the underlying condition is treated. However, full recovery can take several months following a steroid injection. Individuals with diabetes typically exhibit a less favorable response to corticosteroids and may often require surgery. Surgical release of trigger finger has a high success rate and is recommended if steroid injections fail to resolve the condition.[21]

Complications

Open A1 pulley release is generally considered safe with rare complications. Most reported issues are minor, such as scar tenderness, pain, recurrence of triggering, and mild extension lag. Significant complications, including neurovascular bundle injury, bowstringing, and infection necessitating reoperation, occur at an incidence of less than 1% to 4%.[22] Bowstringing of the flexor tendons can also rarely lead to a swan neck deformity.[23]