The carpal tunnel syndrome corresponds to a compression of the median nerve during its passage in the palm of the hand. This median nerve is essential since it ensures the sensitivity of the pulps of the thumb, the index and middle fingers, as well as the motricity of certain muscles of the thumb.

What is carpal tunnel?

The carpal tunnel is an inextensible tunnel limited by the carpal bones at the back (palm bones) and a thick ligament bridging these bones (anterior annular carpal ligament). The median nerve passes inside this inextensible canal, accompanied by the flexor tendons of the fingers. When the canal narrows and/or if the envelopes around the tendons thicken (tenosynovitis), the median nerve will be the first to suffer: the passage of the electric current is slowed down in the nerve by the increase of the intra-canal pressure, and the symptoms appear.

What causes carpal tunnel?

Carpal tunnel syndrome is very common in the general population, with a female predominance. Four out of every thousand people are affected by the pathology. Heavy workers or people with repetitive manual activity (secretary, cashier, assembly line work...) are more often affected than the general population. In some cases, it is possible to be treated as an occupational disease (table of occupational disease n°57 of the general social security system).

Certain diseases, by increasing the thickness of the tendons (tenosynovitis), are often associated with a carpal tunnel: hypothyroidism, diabetes, rheumatoid arthritis.

Pregnancy can also be a factor in carpal tunnel syndrome.

What are the symptoms of carpal tunnel?

Compression of the median nerve as it passes through the carpal tunnel results in sensations of numbness, tingling, or even electrical discharges in the anatomical territory of the median nerve. This one corresponds to the pulp of the thumb, the index and the middle finger (sometimes half of the ring finger). These symptoms can extend to the hand and sometimes to the arm giving the patient a sensation of swollen hand, sleepy, sensation of stopped blood circulation, sensation of clumsiness (the patient drops the objects). We often note a weakness of the thumb-index clamp, a decrease in the strength and muscle mass of the thenar muscles (thumb muscles).

Most often, symptoms appear at night, waking the patient and sometimes requiring him or her to get up and shake the hand for a few minutes to make the symptoms go away. The patient often wakes up around three in the morning.

During the day, symptoms are less frequent and are triggered by certain movements or positions (making a phone call, reading a newspaper, driving, knitting, using a computer or video game).

Finally, the involvement of both hands is very frequent.

What additional tests should be done to diagnose carpal tunnel syndrome?

The electromyogram is the essential complementary examination: it allows to confirm the diagnosis and gives information on the degree of compression of the median nerve during its passage within the carpal tunnel.

The greater the compression, the more the conduction of electricity in the nerve decreases and becomes non-existent in advanced forms of carpal tunnel.

What is the treatment for carpal tunnel syndrome?

Corticosteroid infiltration may be performed in mild forms. The effect obtained is usually only temporary: the signs reappear on average in two to three months.

Surgical treatment remains the reference treatment. Unlike infiltration, recurrence is exceptional (2 to 3 %). The operation consists in opening the thick ligament closing the carpal tunnel in order to lower the intra-canal pressure and thus free the median nerve. It is associated with a cleaning of the inflammation (tenosynovitis) surrounding the tendons.

This intervention will be effective if it is performed within a few months of the onset of symptoms. On the other hand, when a nerve remains compressed for too long, it will be significantly altered and sometimes irreversible. In this case, its surgical release will give less good results.

This operation is usually performed on an outpatient basis (the patient does not stay overnight at the clinic) under locoregional anesthesia (only the upper limb is anesthetized).

The procedure is performed using a minimally invasive technique (the skin opening is small) with or without an endoscopy probe (camera inserted in the hand). These minimally invasive techniques allow for a much faster recovery in the post-operative period. As a result, strict immobilization is short, lasting only 48 hours. Thereafter, the fingers can be moved as normally as possible. However, forceful work and carrying heavy loads must be avoided for three weeks. This is a surgery that is not very painful, since after the operation, the pain usually subsides within one to two days. Thanks to the use of an analgesic, there is little or no pain.

The tingling usually regresses within seven to ten days. On the other hand, severe forms that have been evolving for several years may require several months of recovery to see the symptoms disappear completely or partially.

The ligament is currently healing at six weeks.

The palmar region of the hand, where the carpal tunnel is located, remains sensitive to pressure for three to six months.

A decrease in hand strength of 20 to 30 % also persists for three to six months.

In the case of manual work, three to four weeks off work is usual.

Recurrence is possible, although rare (2 to 3%). It is more present in patients with favourable pathologies (diabetes, hypothyroidism, rheumatoid arthritis...), especially when these diseases are poorly balanced.

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