What is the anatomy of the median nerve and the carpal tunnel?

The median nerve is responsible for sensation in the thumb, index, middle finger, and part of the ring finger (radial hemipulp). It is also in charge of the motor innervation of several thumb and finger muscles.

The carpal tunnel is a narrow osteo-ligamentous tunnel located at the base of the hand, between the wrist and the fingers. It is bordered by the carpus bones deeply and by the volar wrist retinaculum superficially. The median nerve crosses this tunnel together with the flexor tendons of the thumb and fingers. The carpal tunnel is not very expandable as its posterior wall is made up of bones and its anterior wall, the volar retinaculum, is a stiff fibrous structure.

When the size of the carpal tunnel decreases, the median nerve is crushed. This causes the painful symptomatology known as ‘Carpal Tunnel syndrome’.

Most often, the carpal tunnel syndrome is idiopathic, meaning that no specific causes trigger it. The carpal tunnel syndrome has a higher occurrence among women during menopause and pregnancy, and among workers with repetitive tasks (assembly-line, handiwork, or IT).

A few pathologies can also trigger a carpal tunnel syndrome, such as rheumatoid arthritis, carpal bones fractures, hypothyroidism and diabetes.

What are the symptoms of a carpal tunnel syndrome?

At first, the symptoms are mostly subjective signs (sensations experienced by patients) such as tingling, a burning sensation, and numbness. These sensations can sometimes wake patients up at night, who shake their hand in order to eliminate the symptoms. Both hands are frequently affected.

Advanced case of carpal tunnel syndrome can lead to weakness in the hand, loss of strength and amyotrophy (muscle wasting). At this stage, patients lack strength, have difficulties grabbing objects, drop objects, and also experience an important loss of sensation in the first three fingers (thumb, index, and middle finger).

Clinical examination helps the physician to assess the extent of motor and sensation problems. Pain is often experienced when compressing the carpal tunnel or when the wrist is bent for a long time. Associated pathologies, such as trigger finger, may also exist.

Which additional medical investigations should be done?

Electromyographic studies (EMG) are usually performed. They measure the conduction velocity and the latency of the median nerve. It allows the physician to confirm the diagnosis of carpal tunnel syndrome and to assess its severity. This EMG study is performed by a neurologist or by an EMG specialist.

Depending on the patient’s medical history, other medical examinations may be required, such as X-rays, ultrasounds and blood tests.

What treatment?

The medical treatment of the carpal tunnel syndrome consists mainly in corticoid injections performed in the carpal tunnel. These injections are performed during a consultation, about one centimeter above the carpal tunnel. The goal is to inject the corticoid medication in the carpal tunnel in order to decrease the inflammation around the tendons and to make room around the median nerve. Two to three injections can be performed. But the relief is generally only temporary. A night splint can also be used, in association with analgesic medications.

En cas d’échec du traitement médical correctement conduit ou d’atteinte initialement sévère, un traitement chirurgical peut être pratiqué et consiste à ouvrir le ligament annulaire antérieur du carpe pour donner plus de place au nerf médian. Cette chirurgie peut être pratiquée à ciel ouvert (par une cicatrice d’environ 2 cm au niveau de la paume de la main) ou par vidéo chirurgie (chirurgie assitée par caméra avec 1 ou 2 mini cicatrices).

When the medical treatment is not successful, or when the initial extent of the syndrome is too severe, surgical treatment is indicated. The surgical procedure aims at opening the retinacular ligament in order to decompress the median nerve. It can be performed as an open procedure (thus leaving a 2 cm scar in the palm) or as an endoscopic procedure (surgery assisted by a camera, leaving one or two mini-scars).

Most often, the procedure is performed as outpatient surgery under locoregional anesthesia, with no hospitalization.

Once the anterior retinaculum is open, the median nerve can “regenerate”, The most painful sensations, night pain in particular, usually disappear immediately. However, superficial pain around the area of the scar may subsist longer, and it may take up to three months for all symptoms to disappear. When the procedure is performed through endoscopic surgery, the leave of absence is generally two to three weeks long, whereas it can be longer in the case of open surgery.

Any complications?

Carpal tunnel surgery is a common procedure hand surgery procedure. Complications are rare but do exist. The main complications are hematoma, partial nerve lesion, and complex regional pain syndrome (CRPS). Recurrence of the symptoms is rare.

Postoperative regimen

After the procedure, a comfortable dressing is applied for one week.

Scar care is light and the sutures are absorbable. Finger mobilization is started immediately in order to prevent edema.

Whereas night pain disappears quickly, other symptoms might take up to three to six months to completely go away.

After the procedure, simple analgesics (such as acetaminofen and tramadol) are generally sufficient to eliminate pain.

The leave of absence is usually two weeks to a month long.

The degree to which a patient recovers sensation and muscle strength depends on the initial severity and duration of the symptoms before treatment. In cases treated early, without motor deficit, recovery of sensation and strength is usually excellent.