Snap finger (stenosing tenosynovitis of the finger flexors)

Definition

Trigger finger, also called stenosing tenosynovitis, is a disorder in which one of the fingers remains in a bent position, then straightens with a sharp snap (as if a trigger were pulled and released, "trigger finger').

The disease is caused by the narrowing of the synovial sheath surrounding the tendon of the affected finger. The disorder is often painful and, in particularly serious conditions, can cause a real functional block of the affected site.
The trigger finger most commonly occurs in the dominant hand and most commonly affects the thumb, middle or ring finger. The condition can affect multiple fingers at the same time and involve both hands.

People forced to perform repetitive gripping actions, for occupational reasons or for hobbies, are more susceptible to the onset of trigger finger.
Therapeutic treatment varies in relation to the severity and duration of the disorder.

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Symptoms

For further information: Trigger Finger Symptoms

Trigger finger signs and symptoms can be mild or severe and include:

swelling or stiffness of the finger (especially in the morning);
clicking or snapping sensation upon completion of the flexion-extension movement or while firmly grasping an object;
presence of a lump at the base of the affected finger;
pain localized on the palm of the hand;
finger stuck in a bent position, suddenly straightening or, in more severe cases, failing to complete the extension movement.

In case of stiffness or jerks in the joint of a finger it would be advisable to warn the doctor, especially if the affected area is hot and inflamed, as the symptoms indicate the onset of a possible infection.

Snap finger and Dupuytren's syndrome

The trigger finger should not be confused with Dupuytren's contracture, a pathological condition affecting the connective tissue of the palm of the hand. Trigger finger, however, can occur in conjunction with this disorder. Dupuytren's disease is characterized by the progressive and permanent flexion of one or more fingers, caused by the chronic and progressive fibroproliferative lesion of the aponeurosis of the palm of the hand (fibrous band that wraps the muscle to secure it to the bone insertion).

Causes

The main cause that determines the onset of the trigger finger is a narrowing of the sheath that surrounds the tendon of the affected finger. The flexors (superficial and deep) are long fibers that start from the muscles of the forearm, pass into the wrist and insert themselves on the phalanges of the fingers, connecting the muscle to the bone. The tendons are covered by a protective membrane, in turn surrounded by the tenosynovia, which releases a lubricating liquid, which allows the tendon to slide without friction in its membrane, while the finger performs extension and flexion movements.
If the tenosynovial sheath becomes inflamed frequently or for prolonged periods of time, the space within the tendon lining can become narrow and constricting.
The flexor tendons of the fingers do not slide easily through the sheath and force the finger to remain locked in the bent position before extending with a snap. This condition causes irritation and, progressively, an inflammatory process affecting the tendons involved. If the inflammation is prolonged it is possible that scars, thickening (fibrosis) or nodules may arise.
The presence of the synovial swelling increases the tendon's difficulty in overcoming the entrance to the digital channel. To be able to extend the finger, the patient must perform a forced traction, causing the click, associated with a violent pain. The disturbance is very annoying, as it greatly limits the function of the hand.

Risk factors

The risk factors that make you susceptible to trigger finger are:

Microtrauma to the hand.
Repeated gripping movements: a subject is more prone to develop a trigger finger if forced to grasp an object, such as a tool or a work tool (scissors, shears ...), for long periods of time.
Concomitant diseases: patients with certain diseases (rheumatoid arthritis, diabetes, hypothyroidism and some infections) are more at risk of suffering from trigger finger.
Gender: The disorder is more common in women. The incidence in males is lower.

Diagnosis

The diagnosis of trigger finger is essentially clinical: the doctor can diagnose the disorder based on the medical history (clinical history of the patient) and on the physical examination. The physical examination allows the doctor to identify the painful areas, verify the fluidity of the movements by asking the patient to close and open the hand (passage from the flexion to the extension position). With the palpation of the palm of the hand, in correspondence with the "metacarpophalangeal joint, the doctor can detect the presence of any subcutaneous nodules, often painful.