Patient Information Sheet : Lumbar disc excision (Discectomy)Printer friendly version
What Is It?Discectomy literally means removal of disc. The disc is the “shock absorber” between the bones or vertebrae of the spine. There are in fact 33 vertebrae which make up the spinal column and between each one is the disc. Behind this column of bone and disc is a ring of bone which surrounds and protects the spinal cord. Coming out at each level between the bones, very close to the discs, are the nerve roots which spread out into the body. (See Fig 1). The nerve roots from the neck area go into the arm, the nerves from the lower back go into the leg.
The discs allow controlled movement between the vertebrae. The disc consists of a hard outer shell and a soft jelly-like centre. As we get older the disc structure degenerates and begins to wear out. This manifests itself in terms of pain from the splits in the hard outer shell leading to low back pain and dehydration (loss of water) from the jelly-like central substance leading to disc space narrowing and collapse. This is part of the normal ageing process and starts to happen from the age of 25 onwards. Occasionally the degree of wear and tear of the disc progresses to the extent where the small tears form splits which allow some of the disc material in the centre to bulge outwards. This bulge is almost always backwards towards the spinal canal, the spinal cord and its nerve roots.
If the bulge is big enough the nerves can be irritated leading to numbness (pins and needles) in the area where the nerve goes to in the body. As the pressure increases, rather than just being irritated, the nerves are compressed and then nerve function will be affected to the extent where the pain fibres and muscles fibres contained in the nerves stop working properly, and there is severe pain and/or weakness. The bulging disc (so-called prolapsed disc or slipped disc) is a very common condition but thankfully almost always resolves spontaneously. 9 out of 10 disc bulges will improve without the need for surgery or investigation as the tissue heals and the swelling goes down. Rest, in terms of avoiding strenuous exercise (but not bed rest), pain killers and/or anti inflammatories from your doctor and supervised physiotherapy or osteopathy will often help this process. If the pressure on the nerves is sufficiently severe to cause persisting pain, weakness or loss of function then you may be a candidate for surgical removal of the disc prolapse.
Normally the diagnosis is made by your doctor due to the characteristic pattern of symptoms and signs which accompany a slipped disc. However other possibilities have to be excluded which can often present with a similar picture of symptoms and signs, such as arthritis of the hip, arthritis of the sacro-iliac joint at the back of the pelvis and poor blood flow in and out of the legs leading to arterial insufficiency. There can also be trapping of the nerves along the path of the nerve into the limb such as underneath the various muscles and ligaments. In order to confirm the diagnosis and to exclude other possibilities I will normally organise a plain xray which is often normal. Much more accurate is an MRI scan which can show both the soft tissues as well as the bones of the body and confirms first of all that there is a disc prolapse, and secondly that it is causing pressure on the nerves which are giving symptoms.
Discectomy operation is actually the removal of the disc bulge where the nerve and/or nerves are freed up. Although it is called discectomy, the operation really removes the soft centre of the disc rather than the whole disc, but by doing this removes the bulge and tendency to press on the nerves and/or spinal cord.
Why Do We Do It?Discectomy is usually undertaken to resolve or cure nerve pain. Nerve pain (so-called radicular pain) is due to the pressure on the nerve in the spine leading to pain and dysfunction along the course of the nerve. Usually this is for chronic pain and weakness but discectomies can occasionally be carried out as an emergency procedure if the nerve stops working completely or the spinal cord is trapped by a particularly large disc bulge in the centre of the spinal column. If the very large disc bulge trapping the spinal cord occurs below the level of L1 vertebra this situation is known as “cauda equina syndrome”. The operation is very good at resolving nerve root pain and relieving pressure on the nerves but obviously the operation does not return the patient back to normal, it just deals with the consequences of wear and tear on the intervertebral disc and removes some of the disc. However, the operated disc is still abnormal and therefore most patients will still have a degree of low back pain due to that damaged disc. Almost always a damaged disc leading to nerve pressure is as a result of wear and tear changes over many years rather than one single traumatic event. However, the activity which led up to the final insult to the disc which allowed the split to extend to cause a bulge large enough to press on the nearby nerves, is the event which most people remember. In terms of resolving leg pain and dysfunction discectomy of the lumbar disc is successful in around 95% of cases.
Types of DiscectomyDecompression of the disc bulge can be undertaken in many ways. The older techniques involved a large incision or wound in the back and removal of bone from the back of the spine to make a hole big enough to see clearly into the spinal canal, find the nerve root which was damaged and then remove the disc bulge. Newer techniques, such as the MRI scan which allows us to accurately identify which nerve is trapped, xrays in theatre to confirm that the level intended is being operated on and better anaesthetic techniques which allow small incisions to be made without being obscured by excess bleeding, allow the operation to be undertaken through a much smaller incision now, sometimes with the help of a microscope. This is called micro-discectomy and involves no more than a 2” incision between the bones of the levels involved and the operation involves removal of the soft tissues between the bones only, rather than any bony removal. Other ways of removing the disc bulge have been tried using instruments passed through the skin into the disc (percutaneous techniques) and then destroying the disc with a combination of chemicals (chymopapain or enzymes), laser or other heat treatments to burn the soft disc material. Arthroscopic (keyhole surgery) techniques where small instruments are passed down tubes into the disc and pieces of the disc material are nibbled away under vision have also been tried.
Also common a few years ago was a technique known as percutaneous discectomy where an automated cutting machine was put into the disc and pieces of disc material were literally sucked into the cutting arm of the instrument and then chopped off and sucked away. The problems with these percutaneous or keyhole techniques is that they do not allow visualisation of the nerve and the failure rate is quite high, around one third, and in view of that quite often the open micro-discectomy technique is required. Because the micro-discectomy technique can be done through such small incisions and patients are often in hospital for no more than a couple of days, the advantages of these percutaneous techniques over the old types of big operations are no longer valid and the high re-operation rate does not justify these techniques in all but the most selected of cases. The gold standard is the micro-discectomy.
What Are The Risks?Overall discectomy is a very successful operation. Six months after the operation the vast majority of patients (around 95%) feel that the operation has helped sufficiently to have made the operation worthwhile. It is particularly good, and in fact is aimed at resolving the nerve root symptoms, i.e. radicular pain, weakness and sensory loss. It is not aimed at resolving back pain which is often accompanied by leg pain (sciatica) but not as severe as it was. Once the nerve root pain is resolved patients are aware that their back is uncomfortable but it should be pain which is at an annoyance level rather than physically restricting them.
Because 95% of discectomies are successful, this means that 1 in 20 of these operations are not successful. Major complications are thankfully rare but do occur. Deep infection (infection deep into the spine rather than just around the skin) occurs in 1%. Deep vein thrombosis (DVT) and subsequent pulmonary embolus (PE) occurs in around 1%. A massive PE can be fatal and occurs in around 1 in 1000 patients. CSF leakage (loss of fluid from around the spinal cord due to tearing of the dura (the membrane covering the spinal cord and nerves) occurs in around 1 in 25 patients (4%) but often this is insignificant. However, sometimes the leak can be prolonged leading to collection of CSF fluid under the skin or even leakage of fluid through the skin (a CSF fistula). Wrong level surgery, i.e. the surgeon undertakes discectomy at the wrong level, again occurs in around 2 in 100 patients. After the operation, complications such as excessive scarring leading to tethering of the nerve roots (arachnoiditis) or increased back pain due to excessive movement between the vertebrae (spinal instability) can occur and require revision surgery. These complications again are relatively rare, around 2 or 3 in 100. Other major complications can occur, such as anaesthetic complication leading to death, infection getting into the spinal fluid and infecting the spinal cord or even brain (meningitis) and damage to the spinal cord or nerves leading to permanent paralysis often of single muscles but occasionally of the lower legs completely. However, these risks are less than 1 in 1000. Therefore discectomy surgery, although very successful, is by no means minor surgery and there are significant risks. You and your surgeon should attempt to try all means possible to avoid the need for surgery. Your operation should be undertaken by a surgeon who has an interest in spinal surgery and who undertakes more than 20 such operations per year as a minimum.
What Happens In Hospital?Patients who are undergoing discectomy are usually relatively young patients, between 20 and 50. As long as there is no other medical condition, such as diabetes, chest problems, heart problems, etc. the vast majority of patients can be admitted on the day of surgery and undergo operation later the same day under a general anaesthetic. Patients are positioned face down on an operating table with their weight taken on their knees and chest. After an xray is taken to confirm the appropriate level is selected (by placing a needle into the spine and taking an image with the xray machine), I make a small cut between the spines of the vertebrae involved. The muscles are pushed to one side to allow me to see the spinal column and I then make a small window between the bones to get into the spinal canal. The nerve which is being irritated or compressed by the disc bulge is identified and moved out of the way, an incision is made into the disc bulge to allow its removal and also to remove the remainder of the soft centre of the disc so that further material does not come out through the split. Once I am happy that the disc material has been removed and that the nerve is freely mobile, the wound is closed in layers and the skin wound is usually closed with nylon suture.
Following the operation, although your back will be uncomfortable, you will be encouraged to move around as much as possible. This not only helps your nerves at your lower back to recover and to avoid scar tissue forming around them, it also helps generally in getting your muscles moving, your chest working so that chest infection is not a problem and bed sores are avoided. You will be encouraged to stand out of bed on the day of the operation and most individuals should be able to get in and out of bed, walk around the ward within 24 hours of the operation and will be able to go home.