What is the carpal tunnel?
The bones of the wrist are called the carpal bones. They form the floor of the tunnel. The roof is formed by a ligament that joins these bones together and is called the flexor retinaculum. Through the tunnel run the median nerve as well as several other structures including several tendons. Over time the flexor retinaculum becomes thickened and compresses the median nerve.
What is the median nerve and what does it do?
The median nerve is one of the main peripheral nerves of the upper limb. It travels through the forearm and enters the palm of the hand through the carpal tunnel. In the hand, it mainly supplies sensation (feeling) to the thumb, index and middle fingers. It also supplies a group of muscles at the base of the thumb.
What is carpal tunnel syndrome?
The syndrome describes a group of symptoms characteristic of compression of the median nerve at the wrist. The main symptom is numbness and paraesthesia (pins and needles), which may also be painful, that involves the hand and sometimes the forearm as well. It characteristically occurs at night and may wake the patient frequently. It may also occur with activities such as driving or using equipment such as tools that require a strong grip. With increasing severity, the symptoms, especially numbness, become more frequent and even constant. The muscles at the base of the thumb become weak and even begin to waste, that is, become thinner.
In most cases the ligament thickens by itself. However, it is also associated with other conditions such as rheumatoid arthritis. Pregnancy may cause a temporary carpal tunnel syndrome.
How is carpal tunnel syndrome diagnosed?
The most important investigation is the nerve conduction study. This test determines whether the electrical signals travel along various nerves at the speed expected, and whether the whole signal is transmitted, or only part of it. Patients with carpal tunnel syndrome will have abnormal nerve conduction results for the median nerve at the level of the wrist. Patients without this finding are unlikely to have carpal tunnel syndrome and other diagnoses should be considered.
In some cases, an MRI of the wrist is also performed. The MRI will demonstrate the nerve as it passes through the carpal tunnel and whether it is compressed. It will also show any pathological signal changes within the nerve. This is not a standard investigation. However, it can be useful in determining whether the nerve is decompressed in patients that have had unsuccessful surgery in the past and will exclude other potential problems that may mimic carpal tunnel syndrome.
What is the role of conservative treatment?
Some patients with mild symptoms will have benefit from avoiding activities that exacerbate symptoms. Others, particularly those with nocturnal symptoms, will benefit from wearing a wrist splint at night. Some have also used cortisone injections although Prof Owler does not advocate their use in carpal tunnel syndrome.
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