Introduction
Trigger finger (stenosing flexor tenosynovitis) is a condition in which the finger or thumb click or lock when in flexion, preventing a return to extension.
It can affect one or more tendons of the hand, with most cases occurring spontaneously in otherwise healthy individuals. It has a prevalence of approximately 2 in 100 people and can be associated with other conditions, including rheumatoid arthritis, amyloidosis, and diabetes mellitus.
In this article, we shall look at the pathophysiology, clinical features and management of trigger finger.
Pathophysiology
Most cases of trigger finger are preceded by flexor tenosynovitis, often from repetitive movements, leading to inflammation of the tendon and sheath.
Superficial and deep flexor tendons with local tenosynovitis at the metacarpal head subsequently develop localised nodal formation on the tendon, distal to the pulley (Fig. 1). The A1 pulley is the most frequently involved ligament in trigger finger.
When the fingers are flexed, the node moves proximal to the pulley, however when the patient attempts to extend the digit this node fails to pass back under the pulley. Consequently, the digit becomes locked in a flexed position.
Figure 1 – Illustration demonstrating the pathophysiology of trigger finger
The Flexor Sheath and Pulley System
The flexor sheath and pulley system of the digits ensures the flexor tendons remain in the joint’s axis of motion and prevents bowstringing.
There are three types of pulleys involved:
- Palmar aponeurosis – arises from the palmar aponeurosis and is made up of transverse fascicular bands.
- Annular ligaments (5 in total) – A2 and A4 prevent bowstringing; A1, A3, A5 overlie the Metacarpophalangeal (MP), Proximal Interphalangeal (PIP) and Distal Interphalangeal (DIP) joints respectively.
- Cruciate ligamenets (3 in total) – prevent collapsing and expansion of the sheath during movement of the digits.
Risk Factors
The main risk factor for developing trigger finger is having an occupation or hobby that involves prolonged gripping and use of the hand.
Other risk factors include rheumatoid arthritis, diabetes mellitus, female gender, and increasing age.
Figure 2 – Deep flexor muscles of the anterior forearm, forming some of the flexor tendons
Clinical Features
Patients with a trigger finger will often initially report a painless clicking/snapping/catching when trying to extend their finger (most commonly middle or ring finger). More than one finger can be involved at a time and it may be bilateral.
Over time, this may become painful, especially over the volar aspect of the metacarpophalangeal joint, and the digit starts to lock in flexion.
On examination, the proximal aspect of the phalanx should be palpated to assess for any clicking, pain associated with movement, and any lumps or masses.
Differential Diagnoses
- Dupuytren’s contracture – this differs in that the flexion is painless, fixed and cannot be passively corrected
- Infection (within tendon sheath) – usually preceded with trauma and the finger becomes swollen, erythematous, and tender, with passive movement of the digit causes marked pain
- Ganglion – involving a tendon sheath
- Acromegaly – excessive growth hormone results in swelling of flexor synovium within tendon sheath due to increased extracellular volume, limiting both flexion and extension in the affected digit
Investigations
The diagnosis of trigger finger is clinical, however blood tests or imaging may be warranted if any of the above differentials are suspected.
Management
Mild cases of trigger finger can be managed conservatively. Advice regarding activities that cause pain should be given and a small splint can also be used to hold the finger in the extension position at night (this keeps the roughened portion of the tendon in the tunnel which makes it smoother)
For those that do no response to conservative management or are severe, steroid injections can be trialled, which can show improvement over a few days.
Surgical Management
A percutaneous trigger finger release via a needle can be attempted in most cases, involving the release of the tunnel using a needle, performed under local anaesthetic.
For severe cases, surgical decompression of tendon tunnel can be trialled (Fig. 3), whereby the roof of the tunnel is slit, in turn widening its mouth to release the tendon, performed under either a local or general anaesthetic.
Figure 3 – Trigger finger secondary to multiple nodular thickenings along the course of the ring finger’s deep (black arrows) and superficial flexor tendons (white arrow) in the left hand.
Complications
Recurrence of triggering following surgery is uncommon, however adhesions can form if the patient does not begin immediate motion following surgery.
Key Points
- Trigger finger is caused by a localised nodal formation on the tendon, often following cases of tenosynovitis
- It presents with a painless clicking/snapping/catching of the affected digit when attempting extension
- Management is conservative initially, however may require surgical management if there is no improvement or a significant impact on quality of life
