Tactile sensibility in the hand (with the exception of the little finger) is dependent on the major sensory nerve of the hand – the median nerve. At the wrist level, the median nerve passes through a narrow canal – the carpal tunnel – where it is intertwined with several flexor tendons of the hand.
In carpal tunnel syndrome (CTS), the median nerve is entrapped in the carpal tunnel. This can happen due to external pressure, such as swelling in the surrounding flexor tendons sheaths, but most often no cause can be identified. The increased pressure in the carpal tunnel results in impaired microcirculation in the median nerve and damage to the myelin sheaths, surrounding nerve fibres.
In the early stages, carpal tunnel syndrome is characterized by nocturnal numbness and paraesthesia (”pins and needles”) in the fingers except for the little finger. The patient may “wake up because the hand has fallen asleep”. There may be no symptoms in the hand during the daytime. With time the problems may, however, become chronic and troubling also during the day. Even more advanced stages are sometimes characterized by pain and atrophy of the thenar muscles on the base of the thumb.
Carpal tunnel syndrome can be cured surgically by decompressing the nerve through a volar incision dividing the carpal ligament.
About 3 % of the population suffer from CTS, usually middle-aged women. The problem is also common in pregnant women at the last trimester. Many factors can contribute and increase the risk to develop CTS. One important such factor is repeated, monotonous flexion movements of the wrist.
Hard manual work using handheld vibrating tools can cause CTS. While the use of heavy tools combined with monotonous wrist movements may be one reason, the fact that the tools vibrate is probably an important factor in itself. Vibrations from the hand can be transferred to the carpal tunnel and affect the median nerve, which may already be stressed as a result of monotonous wrist movements.
It is important to clarify which problems are caused by vibrations and carpal tunnel syndrome respectively. A surgical procedure aimed at decompressing the median nerve in the carpal tunnel may be curative in the case of problems caused by nerve entrapment, but will have no effect on vibration-induced injuries to nerves in the hand and fingers.