Carpal Tunnel Syndrome

Carpal tunnel syndrome (CTS) describes irritation or damage to the median nerve, one of three nerves in the arm. The nerve runs in the wrist area through the carpal tunnel, a narrow passage formed by the bones of the carpus and connective tissue ligaments (called retinaculum flexorum). In addition, the flexor tendons of the fingers pass through this narrow tunnel.

If there is constant pressure on the median arm nerve in the carpal tunnel area, it can become irritated or damaged, causing carpal tunnel syndrome to develop. In some people, the risk of developing KTS is greatly increased due to anatomy, a narrow tunnel from birth. Under unfavourable conditions, such as a monotonously stressful hand movement at work, the nerve can quickly become irritated. In most cases, the cause is not a congenital narrowing of the tunnel, but rather inflammation and swelling of the tendon sheaths, which also run through the carpal tunnel.

There are various forms of KTS - the symptoms range from a slight numbness in the fingertips to permanent paralysis. KTS usually appears for the first time between the ages of 40 and 70; children very rarely develop the syndrome. Women are affected about three times more often than men.

The cause of carpal tunnel syndrome is that the narrowing of the carpal tunnel irritates the median nerve running through it. In most cases, carpal tunnel syndrome develops when an existing relative anatomical constriction is accompanied by swelling of the tissue due to inflammation, mechanical overstrain or other illness. Factors that promote its development include pregnancy, kidney damage, diabetes mellitus, hypothyroidism, alcohol abuse, wrist injury and one-sided manual work. However, if no primary causes can be identified, the condition is referred to as idiopathic KTS.

Among rheumatism patients (primary chronic polyarthritis), every second patient develops carpal tunnel syndrome in the course of their disease. In one in ten rheumatism patients, KTS is the first sign of their disease.

Increased water retention in the tissue, as can occur during menopause, hypothyroidism, obesity, diabetes or in the last trimester of pregnancy, also promotes the development of carpal tunnel syndrome. In the case of chronic renal insufficiency, the number of patients suffering from KTS increases with the duration of dialysis. The nerve irritation usually first manifests itself in the arm where the shunt (access for the dialysis machine) is also placed. Frequent computer work does not increase the risk of developing KTS.

Often, carpal tunnel syndrome (CTS) begins with an electrifying or tingling sensation in a single finger before later spreading to the insides of the thumb, index, middle and one half of the ring finger. The other half of the finger, as well as the little finger, are supplied by another arm nerve and therefore may not be affected by KTS.

A symptom characteristic of KTS is the hands falling asleep at night. This causes pain in the hand that can travel down the arm to the shoulders, causing sufferers to wake up in the middle of the night. In the early stages of KTS, this discomfort can still be relieved by repositioning the arm. When waking up in the morning, the fingers often feel stiff and swollen. Both hands are affected, but the symptoms are more pronounced in the dominant hand. Over time, the symptoms also increasingly occur during the day.

As the carpal tunnel syndrome progresses, there is a diminished sense of touch and feeling in the affected fingers. The associated disturbance of fine motor skills can go so far that it is no longer possible for the affected person to pick up a pin or button clothes independently.

If the nerve in the carpal tunnel is exposed to excessive pressure over a long period of time, this leads to nerve damage. This causes the pain to disappear, but the fingers remain almost numb. A common late symptom of KTS is atrophy of the ball of the thumb: Since the nerve can no longer transmit stimuli to the muscle, muscle atrophy occurs, causing a dent in the ball of the thumb.

First, the patient's medical history is taken in an anamnesis (medical consultation) so that factors that promote the disease, such as a monotonous workload, excessive muscle training or pregnancy, can also be taken into account. A physical examination is then carried out to check the condition of the muscles of the ball of the thumb and to determine by tapping on the carpal tunnel whether this can trigger pain or discomfort (positive Hoffmann-Tinel sign). In addition, the Phalen test is carried out: in this test, the wrists are bent by pressing the backs of the hands against each other, which should increase the complaints in the case of an existing carpal tunnel syndrome.

However, the diagnosis can only be confirmed by measuring the nerve conduction velocities. This involves measuring the conduction time of the median nerve between the site of stimulation at the wrist and the muscles of the ball of the thumb activated by this nerve. Normal values should be less than 4.2 ms, but these values vary depending on the technique used. Therefore, the velocity should be compared with the values of the ulnar nerve, another arm nerve that does not pass through the carpal tunnel. To confirm the diagnosis of KTS, an examination of the elbow, shoulder area, as well as the cervical spine must rule out other possible sites where the median nerve may be irritated.

Depending on the severity of the irritation, surgical correction must now be considered, otherwise the nerve could slowly die and become irreversibly damaged.

Conservative therapy

Particularly in the early stages of carpal tunnel syndrome, attempts can be made to alleviate the symptoms by wearing special night splints or support bandages during the day. This type of treatment is particularly useful for young people with a short duration of the disease, pregnant women or patients in whom the cause is another disease such as diabetes mellitus or hypothyroidism, which can be treated separately.

The following measures may assist healing:

• Rest the hand and if the overuse is occupational, possibly start there with changes.

• At night, keep the wrist in a normal position with a splint.

• In case of inflammation, injecting cortisol into the carpal tunnel is effective, but not risk-free, as the nerve as well as the tendons could be damaged.

• The effect of diuretics (dehydrating agents) and non-steroidal anti-inflammatory drugs (anti-inflammatory drugs such as acetylsalicylic acid) has not been confirmed.

• Diuretics may be effective in cases of excessive fluid retention in the tissues, as is often the case in pregnancy. However, medication should generally be avoided during pregnancy.

Surgical therapy

If there is no improvement after eight weeks of treatment with conservative therapy, if the condition suddenly deteriorates rapidly, or if the sense of touch is severely impaired due to the nerve disorder, the KTS should be surgically repaired. In most cases, the operation is performed on an outpatient basis under local anesthesia. In the case of local anesthesia, the arm must also be anesthetized, since the arm's lack of blood, which is necessary for the operation, would otherwise cause severe pain.

The following two methods are generally used for the surgical treatment of KTS:

Open surgical technique: this requires a skin incision of about 3cm in the palm. Through this incision, the surgeon cuts the carpal ligament (retinaculum flexorum), a transverse, thickened ligament that spans the bone groove and forms the top of the carpal tunnel. Separation causes the ends of the ligament to diverge, enlarging the carpal tunnel and relieving pressure on the nerve. In addition, tissue, such as severely swollen tendon sheaths, is removed to create additional space.

If there is no previous damage to the nerve, it will recover through the relief of pressure alone and the symptoms of KTS will disappear. The surgical scar is usually almost invisible after six months.

This procedure is one of the most common operations for hand surgeons, usually takes only a few minutes and has a very low complication rate. Typical problems are a reduction in strength of the operated hand over several months, as well as scar discomfort.

Endoscopic surgical technique: Here the surgeon works endoscopically, i.e. from the inside with only an instrumental view of the surgical site. The necessary surgical instruments are inserted through a one to two centimeter long incision along the flexor crease of the wrist. The actual procedure is the same as open surgery.

This procedure has no clear advantages or disadvantages compared to open surgery - a lower scar pain, as well as a higher patient satisfaction with an uncomplicated course is possibly offset by a higher complication rate.

Aftercare

For a better healing of the wound, the wrist is consistently immobilized by a splint for a few days. To avoid swelling, the wrist should be elevated as much as possible. Daily finger and shoulder exercises help to restore mobility as quickly as possible. After about eleven days, the stitches are removed from the surgical site.

Depending on the surgical method, the hand can be used again for light work after one to two weeks. Healing is usually faster with endoscopic surgery than with open surgery. Normally, patients are not allowed to work or do sports for one to three weeks after the operation.

Complications

General consequences of medical procedures, such as postoperative bleeding or infection, rarely occur with this surgery.

With the open surgical technique, the scar may remain sensitive to touch for a long period of time and may cause pain when the hand is subjected to heavier loads. During surgery, the median nerve itself, or a small nerve branch that runs to the thumb, can be damaged. This results in numbness in the fingers and around the ball of the thumb.

Scar complaints occur much less frequently with endoscopic surgery, but there is a higher risk of complications during the operation (damage to the nerves). In some cases, the carpal ligament has to be cut incompletely and the operation has to be repeated. In the case of bleeding or unclear anatomy, there is also the possibility that the operation must be continued using an open surgical technique.

The pain caused by carpal tunnel syndrome usually disappears immediately after the operation, but sensory disturbances in the fingers or muscle weakness in the area of the ball of the thumb usually improve only slowly. Whether the symptoms disappear completely over time depends primarily on how long and how severely the nerve was constricted and whether it has suffered permanent damage as a result. The sensory disturbances can still improve months after the surgical intervention, so it is advisable to have the healing process monitored by a neurologist.

Even if the carpal tunnel has been surgically enlarged, KTS can recur at any time, so care should be taken not to put one-sided strain on the wrists and to continue the finger and shoulder exercises recommended after the operation at a later date.

The development of carpal tunnel syndrome cannot be prevented, but the risk can be reduced by avoiding or treating risk factors (such as hypothyroidism, diabetes mellitus, alcohol abuse or monotonous wrist strain).