Carpal Tunnel Decompression

This surgical procedure aims to relieve patient’s symptoms by taking away compression of the median nerve at the wrist. In the procedure the flexor retinaculum which forms the roof of the carpal tunnel is divided in order to allow more room for the median nerve.

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 a number of tendons. Over time the flexor retinaculum becomes thickened and compresses the median nerve.

The Median Nerve

The median nerve is one of the main peripheral nerves of the upper limb. It travels through the forearm and enters into 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.

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 wakes 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.

Investigations

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 also will exclude other potential problems that may mimic carpal tunnel syndrome.,

Conservative Treatments

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 A/Prof Owler does not advocate their use in carpal tunnel syndrome.

Carpal Tunnel Decompression Surgery

For a relatively simple procedure there are a wide variety of techniques that are used to decompress the median nerve. All aim to divide the flexor retinaculum. Some use the endoscope while others use large incisions. The following is a description of the technique used by A/Prof Owler. It is a common open technique that can be performed under local anaesthesia although in most cases patients prefer a short general anaesthetic.

Before surgery

Prior to surgery, patients may be asked to attend a preadmission clinic. This will involve routine blood tests and for some patients an ECG and chest X-ray. Patients that have significant co-morbidities or illness may require extra assessment. Patients at Westmead Private Hospital will have a pre-operative Doppler of the lower limbs which will be repeated after surgery. This is to assess patients for the presence of deep vein thrombosis (DVT).

Patients who are on aspirin or clopidogrel should cease those medications 7 days before surgery. For patients who are on warfarin, management will depend on the original reason for their warfarin. Some patients will require early admission and be started on heparin, for example, patients with mechanical heart valves. Others will just need to stop taking warfarin 2 days before surgery. The INR will be checked before surgery.

Other medications should be continued including those usually taken on the morning of surgery. These medications should be taken with a sip of water even though the patients may be nil by mouth otherwise

All patients undergoing a general anaesthetic will need to fast. That is, they should have nothing to eat or drink for around 8 hours prior to surgery. Failure to comply with this may necessitate cancellation of the procedure as it may expose the patient to significant risk. As most patients are admitted on the day of the surgery, the hospital will contact them to inform them of the time for admission, likely time of surgery and the required fasting times on the day before the surgery.

Hospital Admission

Except in some circumstances, the operation is performed as a day only procedure. In most instances it will be performed in the morning. The patient will need to come into hospital an hour or so prior to the surgery. They will be told the exact time by the hospital usually on the day before the surgery. Patients need to ensure that if they have MRI scans then they should bring those with them when they come to hospital.

The patient is discharged a few hours after the surgery when the nursing staffs are satisfied. As they will have had a general anaesthetic and will have had an operation on their hand the patient must not drive. They will need to make arrangements for transport to and from the hospital.

Operation

The side of the surgery is checked with the patient prior to the operation. The operation is usually performed under a short general anaesthetic. The region of the wrist is scrubbed and cleaned with antimicrobial solution. The incision is usually around 2-3cm in length and is made in the palm just below the wrist crease. The thickened connective tissue of the flexor retinaculum is then divided. It springs apart to reveal the median nerve. It is then important to check the region above and below the incision to check that the nerve is well decompressed in these areas. After making sure that there is no bleeding, the wound is washed and then sutured together using interrupted nylon sutures. The wound is cleaned and a dressing applied. The patient is then awoken from the anaesthetic and recovered.

After the Surgery

The patient is observed in the day stay suite before being discharged home. At Westmead Private Hospital the physiotherapist will visit the patient and be given instructions on the care of the hand and be instructed on exercises to perform.

On discharge the patient is usually given a script for post-operative analgesic medications. The dressing should remain intact for 48 hours. After that time the dressings should be removed. The wound can be cleaned and can get wet but should not be soaked in a bath or pool for at least 2 weeks after surgery.

Risks of Surgery

While the operation is a relatively small operation, it still has risk. These include a risk of infection of the wound which can usually be simply treated with antibiotics. There is a small risk of wound haematoma formation.

The skin in this region is quite thick. Some people may have a thick or even painful scar. It may be possible to reduce scarring by gentle massage of the region (this should be avoided in the first week after surgery) and by the use of some skin care creams to soften the skin.

The median nerve is on view at surgery and there is a risk of damaging the nerve leading to numbness and weakness. However injury to the main nerve itself is exceedingly rare. A small branch of the nerve which may occasionally run in an unusual course may be more at risk of injury. This branch called the recurrent motor branch of the median nerve supplies some of the muscles that move the thumb. Injury to this branch which is rare can be a significant problem for the patient. The thumb and its strength are important for grip and therefore being unable to pick-up or grasp objects can be disabling for the patient. Therefore although this is rare patients should be aware of this potential complication.

As the operation is performed under a general anaesthetic, there is a small risk of complications related to the anaesthetic itself.

Expectations of Surgery

The outcome from the surgery is dependent on the pre-operative symptoms and their severity. Overall more than 80% of patients will be very satisfied with the results of surgery. The remaining patients often have improvement although sometimes this is not as much as is hoped for. There is a small percentage 1-2% who may have more pain numbness or experience a complication that makes the patient feel worse than prior to the surgery.

Patients with mild to moderate symptoms will do best. These patients generally have paraesthesia and numbness that occur at night and during certain activities such as driving. These symptoms tend to resolve very quickly. Patients with wasting and severe weakness of the thumb muscles do not do as well and will require more time and exercise in order to attempt to improve the strength in these muscles. Patients who have constant numbness will also improve although it is uncommon for numbness to resolve completely and if it does resolve it often takes a matter of months to do so.

Follow-up after Surgery

The sutures need to be removed 10-14 days after the surgery and patients are asked to return to their GP for removal of the sutures. This also provides an opportunity for the wound to be reviewed by their doctor.

Patients are encouraged to return to see A/Prof Owler around 4-6 weeks after the surgery to ensure that the recovery is proceeding as planned and discuss any concerns.

Important Information

This information was provided to assist you. While it has been prepared to provide accurate information the practice and techniques of surgery will differ between surgeons. Likewise the information is a generalisation in relation to the surgery and will vary between patients depending on the individual and their pathology. This information cannot cover all aspects of the surgery especially in relation to surgical risks and should not be considered an exhaustive explanation. Please contact A/Prof Owler’s office if there are any further concerns or questions.