Trigger finger is a common cause of hand pain and functional disability, which is most commonly caused by tenosynovitis of the flexor tendon sheaths. Other causes of trigger finger include direct trauma to the tendon sheaths, especially at the site of the A1 pulley, tendon sheath infection, foreign body, or compression by osteophytes of the heads of the metacarpal and sesamoid bones or abnormal bone growth from other medical conditions such as acromegaly (Figs. 77.1 and 77.2). Repeated irritation from repetitive motion as the tendons pass back and forth over bony prominences and through swollen and stenotic tendon sheaths can cause significant tendinopathy and edema of the tendon sheaths themselves. Over time, if the inflammation remains untreated, nodules may develop on the tendons, which may lock as they pass beneath a retraining tendon pulley causing a triggering phenomenon as the nodule catches on the pulley. When this occurs, the patient experiences a catching or locking of the finger in flexion or extension (Fig. 77.3). Activities associated with the development of trigger finger included repetitive gripping activities involving the hand such as clenching a horse’s reins or steering wheel too tightly. Coexistent arthritis, sesamoiditis, gout, other crystal arthropathies, and synovitis of the metacarpal and interphalangeal joints may predispose the patient to the development of trigger finger.

The pain of trigger finger involving the flexor tendons is localized to the distal palmar surface, with tender nodules often identifiable on palpation of the flexor tendons. Gripping activities exacerbate not only the pain but also the incidence of the triggering phenomenon associated with trigger finger. Often, the patient will awaken to find his or her finger locked in a flexed position with significant morning stiffness as a common complaint. It may require manual assistance to unlock the finger to straighten it. On physical examination, in addition to tenderness to palpation over the tendon nodules
and along the affected tendon, the examiner may appreciate a creaking sensation with flexion and extension of the trigger finger. A triggering phenomenon may be noted, especially if the patient is examined shortly after awakening. An audible pop may be appreciated as the tendon nodule passes over area of tendon sheath stenosis.

Plain radiographs of the wrist are indicated in all patients suspected of suffering from trigger finger to rule out occult bony pathology and to identify calcific tendonitis. Based on the patient’s clinical presentation, additional testing may be indicated, including complete blood cell count, uric acid, sedimentation rate, and antinuclear antibody testing. Magnetic resonance imaging or ultrasound imaging of the hand is indicated to assess the status of the affected tendons and tendon sheath as well as to identify other occult pathology including arthritis, sesamoiditis, and synovitis (Figs. 77.4, 77.5 and 77.6).

The key landmark when performing ultrasound-guided injection for trigger finger is the A1 pulley at the level of the metacarpophalangeal joint (see Figs. 77.4 and 77.6). The most common site of pathology in trigger finger is in the flexor tendon and tendon sheath of the flexor digitorum superficialis and profundus muscles of the second to fifth fingers. Sesamoid bones, bone excrescences, and foreign bodies within the tendon sheath at the level of the metacarpal heads may also contribute to the development of trigger finger (see Fig. 77.6).