Carpal tunnel syndrome
Illustration of the carpal tunnel enclosing the median nerve at the wrist

Definition

Carpal tunnel syndrome is a common condition caused by the entrapment of the median nerve in the carpal tunnel resulting in numbness and significant pain in the hand, fingers and wrist.

Anatomy of the median nerve and its corresponding sensory area

Pathology

The carpal tunnel is a complex anatomical region located at the wrist comprising the carpal bones at the ventral side and the transverse carpal ligament on the dorsal side. The Carpal tunnel encloses the median nerve and the flexor tendons.

The median nerve is formed out of the nerves of the cervical plexus (C6- Th1). it travels along the upper arm, forearm and the wrist to innervate the hand. It controls the sensory function of the lateral side of the palm, thumb, index, the middle and half of the ring finger, but not the little finger and the intrinsic finger muscles. The median nerve innervates the thumb muscle. The flexor tendons allow the fingers and thumb to bend. The carpal tunnel syndrome develops with the compression of the median nerve caused by the swelling of the soft tissue in the carpal tunnel. This type of nerve conditions is generally named entrapment neuropathy, causing pain and numbness in the fingers and hand

Grade 1 Dupuytren's contracture

Classification

The severity of the disease is divided into three grades: 

Grade 1: thickened nodules in the palmar aponeurosis, skin colour changes

 

Grade 2 Dupuytren's contracture

Grade 2: formation of pretendinous and cords, limited finger extension

Grade 3 Dupuytren's contracture

Grade 3: permanent contracture of the affected finger(s)

Manoeuvering a jackhammer causes strong impacts and vibrations detrimental for the median nerve

Causes

The aetiology of carpal tunnel syndrome is unknown. It is thought to origin from one or a combination of the following causes and not from the nerve itself:

Genetic predisposition due to the narrower anatomy of the carpal tunnel

Excessive use of the hand and wrist in specific activities (manoeuvring computer mouse and vibrating tools)

Injury to the wrist (fractures sprains) causing swelling of soft tissue

Age and hormonal changes as it is more common in older individuals and women

Underlying medical conditions such as Rheumatoid arthritis, diabetes and thyroid dysfunction (hypothyroidism)

Cyst formation in the carpal tunnel

Prolonged use of the sewing machine poses a risk for carpal tunnel syndrome

Risk factors

There are a various risk factors thought to cause carpal tunnel syndrome

Adult age and elderly individuals

Females are more often affected possibly due to smaller carpal tunnel anatomy

Dominant hand more susceptible

Arthritis

Metabolic disorders

Professions with intense manual activities: manufacturing, sewing, finishing, cleaning, and packaging.

Atrophy of the thenar muscle below the thumb causes functional weakness in carpal tunnel syndrome

Symptoms

The symptoms of carpal tunnel syndrome begin gradually and increase over time. They include: 

Pain, tingling, burning, and numbness of the thumb, index and inner side of the ring finger. They are more evident while sleeping possibly due to a prolonged bending of the wrist. 

Symptoms are felt mostly on the palmar side of the hand but can extent to the upper arm

Weakening of grip strength

With ongoing pathology: medial nerve damage, muscle atrophy of the thenar muscle and weakness of the thumb movements.

Examination of the median nerve by Tinel's sign, left and testing sensation, right

Diagnosis

Early diagnosis of carpal tunnel syndrome is critical to prevent permanent damage to the median nerve. Clinical examination comprises:

Inspection of both hands, arms, right and left shoulder and neck to exclude other conditions 

Examination of the wrist looking for swelling, warmth, colour and tenderness at touch

Monitoring of sensation in each finger and muscle strength

Use of special tests, Tinel’s test to determine abnormalities of the median nerve (tingling) when it is stimulated with pressure or tapping; and Phalen’s test consisting in bending the fingers towards the wrist, triggering the symptoms above

Electrodiagnostic tests to monitor nerve conduction when stimuli are applied to electrodes placed on the nerve

Electromyography to test median nerve activity directly in the muscle using a needle placed in the muscle and not in the nerve

X-rays to examine bone quality and rule out fractures, arthritis

Other tests to visualise the anatomy of the wrist in particular the soft tissues (ultrasound, MRI)

Blood tests to exclude possible medical conditions

Treatment

Temporary immobilisation of the wrist may be effective in improving carpal tunnel syndrome

Nonoperative treatment

Early conservative treatment is the key for reducing the symptoms of carpal tunnel syndrome. If diabetes and arthritis are present they are given medical priority with medical care. Other measures for conservative treatment are:

Immobilisation of the wrist with a splint for approximately 2 weeks (especially at night) is the first remedy to reduce symptoms of a tunnel carpal syndrome 

Application of cool pads and administration of NSAIDs in case of concomitant swelling and inflammation

Local steroid injections when more severe symptoms are present

Physical and occupational therapy to modify activities and including stretching and strengthening exercises

Other therapies such as acupuncture, chiropractic care and yoga

Scar on the palm following surgery to release the entrapment of the median nerve

Surgical treatment 

In case of prolonged symptoms despite conservative treatment, surgery is necessary. This aims to release the entrapped median nerve. The success rate of surgery is very high.Two surgical approaches are available:

Traditional surgery: Incision along the wrist and palm. The transverse carpal ligament is cut to reduce the pressure on the medial nerve. The skin over the median nerve is sutured together. During the healing process the ligament will repair itself maintaining a larger tunnel size for the nerve and flexor tendons. 

Endoscopic surgery: An alternative, minimally invasive approach that reduces the wound size and allows for faster recovery. Two small incisions in the wrist and palm are made to insert an endoscope (camera) to visualise the region and the second for the surgical tools. The surgical procedure remains the same as in the traditional approach as in cutting the transverse carpal ligament.  

Stretching exercise of the wrist

Rehabilitation 

Post-operative

After surgery the initial care includes:

Immobilisation with a cast or splint for up to 3 weeks

Hand elevation

Treatment with analgesics and NSAIDs

Ice pads to reduce inflammation and swelling

Use of the hand can commence immediately after surgery while wearing a brace or without minor symptoms may remain for a few months after surgery. Strength of grasping activity may return after 4 weeks post-surgery and full recover can take up to 1 year. A number of exercises guided by a physiotherapist will assist in gaining strength of the operated wrist.

Above, wrong, and below, correct posture of the wrist when using the mouse

Prevention

Although the causality of manual work and the carpal tunnel syndrome remains unclear, a number of measures including occupational health and safety rules at workplace should be implemented to reduce the risk to develop a carpal tunnel syndrome. These recommendations include:

Ergonometric education for correct posture during manual activities (avoid to keep the wrist bent)

Wear gloves or splints

Use workstations designed for optimal posture of hand and wrist

Regular stretching exercises while working

Frequent rests when involved in heavy industrial manual work

Job rotation amongst employees