Definition

Trigger finger is the snapping, triggering, or locking of a finger as it is flexed and extended. This is due to hypertrophy and fibrocartilaginous metaplasia at the tendon-pulley interface that does not allow the tendon to glide normally back and forth under the pulley. Trigger finger is thought to arise from high pressures at the proximal edge of the A1 pulley when there is a discrepancy in the diameter of the flexor tendon and its sheath at the level of the metacarpal head [1] (Fig. 37.1). The thumb (33%) and the ring finger (27%) are most commonly affected in adults, but 90% of pediatric trigger fingers involve the thumbs, 25% of which are bilateral [1]. It is often encountered in patients with diabetes and rheumatoid arthritis [2,3]. The relationship of trigger finger to repetitive trauma has been cited frequently in the literature [3–5]; however, the exact mechanism of this correlation is still open to debate [6]. Rarely, it is due to acute trauma or space-occupying lesions [7–9].

Symptoms

Patients typically complain of pain in the proximal interphalangeal joint of the finger, rather than in the true anatomic location of the problem—at the metacarpophalangeal joint. Some individuals may report swelling or stiffness in the fingers, particularly in the morning. Patients may also have intermittent locking in flexion of the digit, which is overcome with forceful voluntary effort or passive assistance. Involvement of multiple fingers can be seen in patients with rheumatoid arthritis or diabetes [2,3]. In one study, the perioperative symptoms differed for trigger thumbs versus trigger fingers [10]. In this study, patients complained of pain with motion with trigger thumb; with trigger finger, they complained primarily of triggering and loss of range of motion.

Physical Examination

The essential element in the physical examination is the localization of the disorder at the level of the metacarpophalangeal joint. There is palpable tenderness and sometimes a tender nodule or crepitus over the volar aspect of the metacarpal head. Swelling of the finger may also be noted. Opening and closing of the hand actively produces a painful clicking as the inflamed tendon passes through a constricted sheath. With chronic triggering, the patient may have interphalangeal joint flexion contractures [11]. Therefore it is important to determine whether there is normal passive range of motion in the metacarpophalangeal and interphalangeal joints. Neurologic examination findings, including muscle strength, sensation, and reflexes, should be normal, with the exception of severe cases associated with disuse weakness or atrophy. Comorbidities can affect the neurologic examination findings as well (e.g., patients with diabetic neuropathy or carpal tunnel syndrome may have impaired sensation).

Functional Limitations

Functional limitations include difficulty with grasping and fine manipulation of objects due to pain, locking, or both. Fine motor problems may include difficulty with inserting a key into a lock, typing, or buttoning a shirt. Gross motor skills may include limitation in gripping a steering wheel or in grasping tools at home or at work.

Diagnostic Studies

This is a clinical diagnosis. Patients without a history of injury or inflammatory arthritis do not need routine radiographs [12]. Magnetic resonance imaging can confirm tenosynovitis of the flexor sheath, but this offers minimal advantage over clinical diagnosis [13]. Alternatively, a diagnostic ultrasound examination can show tendon nodules, tenosynovitis, and active triggering at the level of the A1 pulley.

The goal of treatment is to restore the normal gliding of the tendon through the pulley system. This can often be achieved with conservative treatment. Typically, the first line of treatment is a local steroid injection [14]. The determination of whether to inject first or to try noninvasive measures is often based on the severity of the patient’s symptoms (more severe symptoms generally respond better to injections), the level of activity of the patient (e.g., someone who needs to return to work as quickly as possible), and the patient’s and clinician’s preferences.