Results and Complications of Spinal Surgery
If the operation is done for the right reasons (that is, if the criteria are followed), then the success rate should be at least 90%. That also means that up to 10% of people (1 in 10) will have a complication. Some people may have incomplete relief of symptoms.
It is important to remember that most people will have some leg pain after the surgery and this pain often comes and goes especially in the first six weeks. This is to be expected. Incomplete relief refers to continuing symptoms that do not go away. The symptoms may include leg pain, numbness, pins and needles or weakness. It is often minor and no more than an inconvenience but occasionally can be severe. It happens most commonly due to nerve damage that has occurred while the disc prolapse has been pressing on the nerve. Simple removal of the pressure does not always mean the nerve functions normally straight away. An analogy I use is dropping a brick on your foot – taking the brick off gets rid of a lot of the pain but some pain continues. If the brick has caused enough damage, some of the pain may never go away. The nerve may continue to recover after discectomy for up to two years (this especially applies to weakness in the foot) but the majority of recovery occurs within the first three months. The other reason you may have incomplete relief is that all of the pressure has not been removed. This may be because some of the disc material has been left behind, because there is some pressure due to bone overgrowth that has not been removed, or that the wrong level or side has been operated on. This is mentioned below.
The list below is long and daunting. You must remember however that these complications occur in only 10% of people; that is, 1 in 10. However if it happens to you, then it is still serious, no matter how uncommon it is.
Recurrent disc prolapse
At the time of discectomy, only the prolapsed piece of soft disc is removed, together with any other loose fragments within the disc space. This means that it is possible that more of the soft disc material can prolapse out in the future. If this happens, the leg symptoms come back like before and do not settle after a few days. Often the surgery needs to be repeated. This complication happens very uncommonly within the first three months after surgery, but can occur after this up to years following surgery. It is difficult to avoid this, as it does not seem to matter whether more or less of the soft inner disc is removed at the time of surgery as to whether a recurrent prolapse will occur.
Nerve scarring (epidural fibrosis or arachnoiditis)
Scar tissue always forms in the area of discectomy, due to healing of the defect in the outer disc and due to bleeding and stretching of the nerve root. The scar itself is painless, but if it is excessive, it can constrict the nerve and restrict its movement. Sometimes this leads to leg pain. The pain is often different to the original pain in that it is a constant burning ache. The risk can be minimised somewhat with careful handling of the nerve and control of bleeding. Some surgeons believe that scar can be minimised by placing something over the nerve root. I use a thin piece of fat taken when the cut in the skin is made. There is a gel that is available to put on the nerve instead, but it is expensive and not fully proven to work.
Because the surgery involves cutting and stretching muscle, and cutting and removing disc, there is a possibility that back pain will occur after surgery. You must remember that most people will have some back pain for a few weeks after the operation, but it may become severe and constant in a small group of people. Some people need a spinal fusion because of the pain, but this is quite uncommon.
This is most often due to bruising or stretching. This is more likely to occur if the disc prolapse is large, the spinal canal is narrow, or the rare case where two nerve roots are joined (conjoint nerve root). Such damage usually recovers, but for a period of time at least, there may be weakness or discomfort in the area that the nerve supplies. More serious is if the nerve is severed or divided. This occurs when the nerve is not seen or recognised while the space is being created, or the disc prolapse is being removed. If this occurs, there will be some permanent loss of function of the leg but the degree and area varies depending on which nerve is involved. For example, if the L5 nerve is damaged, you may develop a foot drop, where you cannot lift the foot and it drags. If the S1 nerve is damaged, you may develop weakness of your calf and cannot stand on tiptoes on that side.
This is a rare but disastrous complication. Complete paralysis occurs in about 1 in 50 000 patients. Partial paralysis may be more common but is still very infrequently seen. Sometimes the cause cannot be explained. The most common cause is thought to be an epidural haematoma, where bleeding occurs in the spinal canal and pressure due to the blood clot increases to the point where all the nerves are squashed. This risk can be minimised by careful control of bleeding and avoiding any drugs that may increase your risk of bleeding after the surgery. If it occurs, there is worsening pain, numbness and weakness in the legs together with loss of the ability to pass urine. If this occurs, the treatment is urgent evacuation of the haematoma; in other words, surgical removal of the blood clot.
Unrecognised bleeding can occur within the spinal canal or within the wound. If it occurs within the spinal canal, it may lead to an epidural haematoma, which is discussed above. If it occurs in the skin or muscles of the wound, the wound may become swollen. Usually this settles down within a week, but if the wound begins to bleed or open up, it may be necessary to go back to surgery to remove the haematoma and re-suture the wound.
To minimise the chance of infection, antibiotics are given in theatre just before the cut in the skin is made. Nevertheless, a wound infection can still occur, especially if a haematoma has developed. This may require another trip to theatre to have the wound washed out and re-sutured. Intravenous antibiotics (through the drip) followed by oral antibiotics (tablets) will also be required for a period. A much more serious infection (but fortunately more rare) is that which occurs in the disc. This is called discitis. It may spread into the spinal canal and is then known as an epidural abscess. If the infective tissue presses on the nerves, urgent surgery may be required to remove it. Otherwise it is treated with long-term antibiotics. The infection usually settles, but may progress to bone damage and collapse or continuing infection, and major surgery may be required to remove the infection and fuse the spine.
The thin tissue forming the fluid-filled sac that the nerves are in may be torn during the surgery. This is much more common if there has been previous surgery in the area, with resultant scar and adhesions. If a dural tear occurs, it can usually be repaired successfully. After surgery you must lie flat for two days as a precaution to decrease the pressure at the area of the tear to allow it to heal. Sometimes the tear does not heal, it cannot be repaired completely, or it is not noticed at the time of surgery. The result is continuing leak of spinal fluid. This may either collect in the wound or under the skin, or it may leak through the wound. If this occurs, it is usually necessary to go back to theatre to have the tear repaired. A very rare complication of a spinal fluid leak is meningitis.
Injury to abdominal contents
In front of the disc is the abdomen; in particular the big arteries and veins to the legs, and the bowels. If the instrument used to grab the disc is pushed too far, it may go through the front of the disc and cause damage to these vital structures. This is exceedingly rare, but may cause massive bleeding requiring emergency abdominal surgery, or abdominal infection. Either of these could lead to death.
A relatively common complication after any surgery is the development of clots in the legs. The risk is that these may get bigger, break off and travel to the lungs. This is called a pulmonary embolism, and can be fatal. The chance of this occurring after discectomy is very small, and is minimised by wearing special compressive stockings, and getting out of bed and walking as soon as possible after surgery, usually on the same day. The risk of clots is increased if you have had them before, and extra precautions may be required in this case.
This is something you need to discuss with your anaesthetist. A list of complications you should consider are:
1. stroke or heart attack
2. chest infection from aspiration or lung collapse
3. damage to teeth during insertion of the tube
4. pressure due to your position on the operating table, especially on nerves such as the ulnar nerve in the elbow, leading to tingling in the hands, or on your eyes, causing vision problems
This is something every surgeon fears – operating on the wrong disc or on the wrong side of the disc. To minimise the chance of this happening, I ask you to mark the leg you have the pain in with an arrow on the thigh, using a marker pen. When you are asleep on the operating table in the position for surgery, I put a needle in your back in line with where I think the prolapsed disc is, and check this with an x-ray (using a video-like machine called an image intensifier or fluoroscope). Even with all these precautions, sometimes the wrong spot is opened. As long as this is recognised, little harm is done by moving to the right spot, except for the fact that the wound is a little longer.