Flexor Pollicis Longus Tendon Injection for Tendinitis and Trigger Thumb

Indications and Clinical Considerations

Trigger thumb is caused by inflammation and swelling of the tendon of the flexor pollicis longus as a result of compression by the head of the first metacarpal bone. Sesamoid bones in this region also may cause compression and trauma to the tendon ( Fig. 87.1 ). The inflammation and swelling of the tendon are usually a result of trauma to the tendon from repetitive motion or pressure overlying the tendon as it passes over these bony prominences. If the inflammation and swelling become chronic, thickening and deterioration of the tendon sheath occur, resulting in constriction of the sheath. Frequently, a nodule develops on the tendon because of chronic pressure and irritation. These nodules often can be palpated when the patient flexes and extends the thumb. Such nodules may catch in the tendon sheath and cause a triggering phenomenon, thereby causing the thumb to catch or lock.

Arthritis and gout of the first metacarpal joint also may coexist with and exacerbate the pain and disability of trigger thumb. Trigger thumb occurs in patients engaged in repetitive activities that include hand grasping, such as politicians shaking hands, or activities that require repetitive pinching movements of the thumb. Video games and frequent card playing also have been implicated in the evolution of trigger thumb ( Fig. 87.2 ).

The pain of trigger thumb is localized to the palmar aspect of the base of the thumb in contradistinction to the pain of de Quervain tenosynovitis, in which the pain is most pronounced more proximally over the radial styloid. Trigger thumb pain is constant and made worse with active pinching activities of the thumb. Patients note the inability to hold a coffee cup or a pen. Sleep disturbance is common, and often patients awaken to find the thumb has become locked in a flexed position during sleep. Physical examination reveals tenderness and swelling over the tendon with maximal point tenderness over the base of the thumb. Many patients with trigger thumb exhibit a “creaking” sensation with flexion and extension of the thumb. Range of motion may be decreased because of the pain, and a trigger thumb phenomenon may be noted. Patients with trigger thumb often demonstrate a nodule on the tendon of the flexor pollicis longus.

Plain radiographs are indicated for all patients with trigger thumb to rule out occult bony disease. On the basis of 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 of the hand is indicated if first metacarpal joint instability is suspected ( Fig. 87.3 ). The injection technique described later serves as both a diagnostic and a therapeutic maneuver.

Clinically Relevant Anatomy

The nidus of pain from trigger thumb is the tendon of the flexor pollicis longus at the level of the base of the first metacarpal (see Fig. 87.1 ). Sesamoid bones present in this region may also impinge on the tendon and tendon sheath, causing inflammation and swelling. As mentioned earlier, arthritis and gout of the first metacarpal joint may accompany trigger thumb and exacerbate the patient’s pain symptoms. The radial artery and the superficial branch of the radial nerve are in proximity to the injection site for trigger thumb and may be traumatized if the needle is placed too medially.