Trigger finger
Trigger finger, Digital flexor tenosynovitis, Stenosing tenosynovitis

Definition

Trigger finger and trigger thumb consist in the altered movement causing an involuntary catching when flexing the finger towards the palm. In severe cases the fingers are locked in a flexed position and cannot be straightened.

Pathology

Trigger finger is a pathology of the flexor tendon, which connects the phalanges to the muscles in the palmar side of the forearm. The tendon is aligned with the finger and fixed by lateral ligaments named pulleys. The tenosynovium sheath encloses the tendon to facilitate its gliding when the finger is extended or flexed.

In trigger finger the irritated flexor tendon and pulleys become swollen occasionally leading to the formation of a nodule, which limits or blocks the sliding of the tendon during movement. A typical catching and popping noise can be heard during grasping function.

Arm abduction is restricted by the inflamed bursa and tendons, reducing the joint space
Cross section of the shoulder depicting the compression of the bursa (red) above the rotator cuff (white) and below the deltoid muscle

Classification

There are various classification systems for a shoulder impingement syndrome.

Stages of subacromial impingement in athletes - Jobe’s Classification
(1989):

Pure impingement with no instability

Primary instability, with capsular and labral injury with secondary impingement, which can be internal or subacromial impingement

Primary instability due to intrinsic ligament laxity with secondary impingement

Pure instability with no impingement.

Grading of impingement changes - Milgrom’s Ultrasound Classification:

Stage 1 Bursal thickness from 1.5 to 2.0 mm

Stage 2 Bursal thickness over 2.0 mm

Stage 3 Partial or full thickness tear of the rotator cuff.

Impingement lesions - Copeland Levy Classification:

This is based on the location of the impingement, either on the acromial or the bursal side.

Acromial side

A0 normal - smooth surface

A1 minor deterioration, haemorrhage or local inflammation

A2 marked scuffing/damage of the undersurface of the acromion and coraco-acromial ligament

A3 exposed bone areas.

Bursal side

B0 normal - smooth surface

B1 minor deterioration, haemorrhage, inflammation

B2 major deterioration of the cuff, partial thickness tear

B3 full thickness tear of the rotator cuff

B4 massive cuff tear.

Two-part proximal humerus fracture

According to the Habermeyer Classification the fractures to the proximal humerus are divided into:

Type 0 one fractured part without dislocation

Type A two-part fracture of the great tuberosity and lesser tuberosity avulsion

Type B involves the humerus “surgical” neck below the femoral head as two-part, three-part and four-part with one or both tuberosities

Type C involves the humerus anatomical neck (between the head and greater tuberosity) as two-part, three-part and four-part with one or both the greater and lesser tuberosities.

These are defined further as:

One-part fractures are non-displaced fractures or fractures with minimal displacement

Two-part fractures only involve a single segment

Three-part fractures involve two segments

Four-part fractures occur when all humeral segments are involved (see image in pathology section)

The injury severity is proportional to the increasing number of fractures.

Three-part proximal humerus fractures

Operating hard tools can cause stress and inflammation of the flexor tendons and consequent trigger finger

Causes

The irritation of the flexor tendon causing trigger finger is mostly a consequence of overuse of the hand; however the aetiology of this pathology remains unknown. The condition is more frequent in women and the adult/aged population. Apart from repetitive grasping/gripping function other causes leading to trigger finger include:

Tear to the flexor tendon

Infection of the synovium

Congenital condition predisposing to tendon nodule formation

Prolonged driving is a risk factor for trigger finger pathology

Risk factors

Although risk factors leading to trigger finger have not been identified, the following factors may pose a risk:

Female gender

Age between 40 and 60 years

Occupational activities: repetitive gripping of power tools

Prolonged driving (grasping the steering wheel)

Daily activities: writing, carrying bags and briefcases

Medical conditions: diabetes increases four times the risk, rheumatoid arthritis

Inability to fully extend the finger as the inflamed tendon is entrapped in the synovium

Symptoms

The symptoms arising from a trigger finger are:

Pain at the nodule site when flexing and extending the finger

Swelling

Clicking sensation when flexing the finger

Impaired finger extension

Movement restrictions (grasping) especially after inactivity

Blockage of the finger in a bent position

 

Medical examination determines changes in the anatomy and function of the fingers
Left: X-ray of trigger thumb with mild osteoarthritis at 1st IP joint; Right: ultrasound shows the thickened, inflamed flexor tendon

Diagnosis

The diagnosis of trigger finger does not require special tests or X-rays. Medical examination is based on:

Observation of the hand anatomy

Palpation to detect the presence of nodules at metacarpo-phalangeal or proximal-phalangeal joints

Assessing changes in finger flexion/extension, stiffness, pain level when opening/closing the fist 10 times

Audible clicking/popping noises

Treatment

Steroid injection within the area of tendon inflammation

Nonoperative treatment

Conservative treatment is the most common and efficacious management of trigger finger. if the condition has not been protracted over four months, physiotherapy and occupational therapy will restore successfully finger function. Conservative management also include:

Immobilisation of the fingers with a splint until the inflammatory condition has subsided

Heat application

Administration of NSAIDs

Local steroid injection

Painkillers

Illustration showing the pulleys that are severed to allow tendon sliding within the synovium

Surgical treatment

Surgery is required in case of severe and prolonged trigger finger symptoms. It consists in the resection of the pulleys at the nodule zone to free the tendon during movement. This an outpatient procedure performed under local anaesthesia. Methods such as endoscopic surgery and percutaneous tendon release are available providing a faster postoperative healing.

Complications

Complications following a surgical treatment of trigger finger are:

Limited straightening of the finger (insufficient tendon release)

Hyperextension of the finger (excessive tendon release)

Ongoing trigger finger

Infection

Ball exercises are useful for rehabilitative treatment of trigger finger

Rehabilitation

A physical or occupational therapist will guide stretching movements to restore flexibility and physical exercises to strengthen the fingers and re-acquire fine motor control. Physiotherapy is recommended for 6 weeks. Full recovery after surgery can take up to 6 months. Advice on modifying daily activities is provided to avoid excessive stress on the affected tendon.

Adopting a correct posture and movement of the hand and fingers can prevent trigger finger

Prevention

There are no specific measures to prevent trigger finger. The best strategy is to avoid excessive strain of the flexor tendon during occupational and daily activities.