Introduction

The bones of the thumb consist of one metacarpal bone and two phalanxes (proximal and distal, respectively). This anatomy varies in comparison to the other fingers which have three phalanxes (proximal, middle, and distal). Other bony constituents of the thumb are sesamoid bones which can be found in the other fingers. The unique function of the thumb is attributed to two movements:  opposition and apposition. Additionally, at the metacarpophalangeal (MCP) joint, the thumb can flex, extend, abduct, and adduct.

Trigger thumb is a simple term for stenosing flexor tenosynovitis of the thumb. This is a narrowing of the flexor tendon sheath which causes a clicking or popping sensation on attempted extension of the thumb. Flexion is normally enabled by the extrinsic flexor pollicis longus (FPL) and intrinsic flexor pollicis brevis (FPB). The FPL tendon runs in its tendon sheath through three pulleys (A1, oblique, and A2) located proximal to distal. The A1 pulley is located distally on the metacarpal bone overlapping the MCP joint and the base of the proximal phalanx. Trigger thumb is most commonly due to thickening of the A1 pulley which causes pain and decreased function.[1][2][3][4][5]

Etiology

The main cause of trigger thumb is idiopathic; however, it has been associated with overuse and repeated gripping maneuvers. Several diseases predispose an individual to this condition. These can be diabetes mellitus, amyloidosis, and rheumatoid arthritis. [6][7][8]

Epidemiology

Trigger finger is one of the most common complaints by patients presenting to their primary care physician. It is estimated there are more than 200,000 cases per year in the United States. It is seen more commonly in women between the ages of 40 to 60, although it can present as early as birth in some children. In children, it typically presents as trigger thumb.

History and Physical

Complaints can vary from mild to moderate severity and with early symptoms of soreness at the base of the thumb close to the MCP joint. Progression of symptoms includes pain and stiffness when flexing the thumb, swelling, or a tender lump on the head of the metacarpal on the palmar side of the hand. Locking of the thumb in the flexed position can be seen in severe cases. The patient must gently straighten the thumb with the help of their other hand. When the thumb releases from the locked position, there can be a snapping or popping sensation. Other complaints include the inability to extend the thumb fully.

On examination, patients are tender at the MCP joint and are reluctant to allow the examiner to extend the digit. A popping sensation is felt with an observed snap into extension. Trigger thumb can be classified based on Quinnell grading system for flexion and extension.

• 0 Normal movement
• I Uneven movement
• II Actively correctable
• III Passively correctable
• IV Fixed deformity 

Evaluation

Trigger thumb is a clinical diagnosis based on history and physical exam. In the physical exam, the hands should be placed with the palms up in a relaxed position. The patient is asked to slowly actively flex and extend the fingers in an attempt to try to make the finger lock or catch. The provider can facilitate this by further flexing the digits of the patient. Alternatively, if active triggering is not present, the examiner places their fingers on the MCP joint as the finger is actively flexed and extended, noting the presence of a clicking sensation or loss of smooth motion. Locking may not occur with each motion.

Several differentials should be kept in mind when evaluating for trigger thumb. Such differentials include infectious tenosynovitis, non-infectious tenosynovitis, and metacarpophalangeal joint sprain. Infectious tenosynovitis presents with severe pain, decreased range of motion, warmth, erythema, and tenderness to palpation over the flexor tendon sheath. Evaluation should assess for minor trauma such as lacerations, punctures involving the thumb or hand. Early recognition is of utmost importance, as closed-space infection can cause tendon rupture limiting motion of the thumb. Non-infectious tenosynovitis also presents with pain, tenderness, and swelling along the flexor tendon. Underlying inflammatory arthritis, such as rheumatoid arthritis or reactive arthritis commonly link to non-infectious tenosynovitis. Unlike trigger finger, noninfectious tenosynovitis involves swelling and pain along the long axis of the affected tendon and joints. Treatment with nonsteroidal anti-inflammatory drugs (NSAIDs), disease-modifying antirheumatic drugs (DMARDs), and systemic glucocorticoids improve symptoms markedly. A metacarpophalangeal joint sprain is commonly due to trauma. Patients will complain of tenderness on either side of the MCP joint associated with loss of full flexion; however, no clicking sensation is present.

Differential Diagnosis

• Congenital stiffness of the distal interpharyngeal joint of the thumb

• Hyperflexible thumb

• Thumb hypoplasia

• Thumb -in – palm deformity

Enhancing Healthcare Team Outcomes

The diagnosis and management of trigger thumb is with an interprofessional team that consists of the primary care provider, nurse practitioner, hand surgeon, plastic surgeon, orthopedic surgeon and physical therapist. Healthcare workers who initially see patients with a trigger thumb should refer them to a hand surgeon and let him/her make the decision about treatment. Practitioners base treatment of trigger thumb on severity and duration of symptoms. Initial treatment entails conservative management and adjunctive pain relief. In addition, physical therapy is a key part of treatment. If the patient fails to improve, surgery may be an option. A variety of procedures have been developed to treat trigger but not are always 100% successful. Residual pain, recurrence and limitation of thumb motion are seen in a fair number of patients, even after adequate physical therapy.[13][9] (Level V)