What is back pain?
Low back pain is one of the commonest medical conditions in our community. It is important to make a distinction between back pain and sciatica, as the treatment is different, even though they may both be caused by similar conditions. Sciatica implies pain in the leg due to irritation of one of the nerve roots that make up the sciatic nerve. This pain usually radiates down the back or the side of the leg and extends below the knee, often into the foot. It is frequently associated with numbness or pins and needles and may also cause weakness in the leg. Back pain may be referred to the groin or thigh, in much the same way as a heart attack can cause pain in the arm, but this should not be confused with true sciatica.
What is degeneration?
The normal spine gradually deteriorates over a lifetime. This starts very early, in our twenties, and progresses at different rates in different people. The changes that occur are often referred to as degeneration, arthritis or spondylosis. These all mean the same thing. A healthy disc contains a high proportion (over 80%) of water and one of the earliest signs of degeneration is a decrease in the water content as the disc “dries out” or dessicates. This is often asymptomatic and may be seen as a change in the colour of the disc from white to black on MRI or a loss of disc height on xray or CT. At the same time as the disc degenerates, so do the facet joints. These are small joints in the back of the spine that are similar in size to knuckle joints and they also tend to enlarge as they become arthritic. The picture below shows one normal facet joint and an enlarged, irregular, arthritic joint (arrow).
What is a disc prolapse?
The disc is composed of two parts. The outer part, or annulus, is composed of many fibres that join the vertebrae together. In cross section this has a similar appearance to the rings of a tree trunk. In the middle is the nucleus, which is the soft part of the disc. This contains a large proportion of water and gradually dries out and shrinks with age, causing the disc space to narrow. Small tears appear either between or across the layers of the annulus. These can occur with minor injury or normal everyday life.
Disc tears may sometimes be seen on an MRI as a white area of high signal (red arrow) but often the only change is a loss of signal as the water content decreases (compare the normal white disc with the abnormal black disc).
Disc tears may be painful but this pain is not relieved by doing a discectomy, as this only removes the nucleus of the disc which has no pain fibres in it. If several of these small tears join together, or less commonly if there is a major injury causing a single large tear, the nucleus (central, soft part of the disc) may squeeze out through the tear. This is called a disc prolapse or herniation or “slipped disc” and is shown by the red line in the scan below. In this situation, the disc may press on a nerve and cause sciatica (leg pain).
What is a disc bulge?
A generalised disc bulge is a different situation and is due to loss of height of the disc due to loss of water in the nucleus. As the nucleus shrinks and the disc becomes narrower, the fibres of the annulus remain the same length and consequently bulge out to the side, just like a shirt sleeve that is pushed up the arm.
In this picture, the disc can be seen bulging all the way around the margin of the bone, rather than in one focal area as is seen with a prolapse. A disc bulge like this does not usually cause sciatica.
How is chronic back pain treated?
In most cases, surgery is of no value in the treatment of back pain. As the most common cause is arthritis, the most common treatment is anti-inflammatory medication. This is usually combined with physiotherapy, in particular an exercise program to reduce weight and improve the strength of the back and abdominal muscles which help to support the spine. The most commonly utilised program at present is the Pilates method. Your physiotherapist can instruct you on this or you can do the exercises at home with the help of a book or video.
There are a variety of other medications that can be of value in chronic back pain. Apart from painkillers, there are two types of drugs that can sometimes help; antidepressants and anticonvulsants. In smaller doses than for their primary use, they can have an effect on chronic pain and reduce the need for analgesics.
Facet joint injections
When the facet joints are very degenerate, some relief may be obtained from injection of steroid into the joint space. This is done by a radiologist under CT control, usually with some sedation. If the injections produce relief for a reasonable period, they may be repeated.
Injection of steroid into the epidural space (the space around the nerves in the spinal canal) can sometimes be very beneficial for sciatica but is of no benefit for back pain.
There are some occasions where surgery to fuse the spine can be of benefit in chronic back pain. This is usually when the pain is related to one specific disc in the back and the remaining levels are relatively healthy. Spondylolisthesis is a condition where there is instability at one spinal level and it may respond to a fusion. A thorough trial of conservative treatment is always undertaken prior to considering surgery for back pain. Disc replacement is popular in some countries but has serious shortcomings and has not been proven to be superior to fusion.
Laser, IDET, etc
There are a variety of treatments which may be promoted as almost magical cures for back pain. Most have had no or very little scientific assessment and the claims are often based on personal opinions. When scientific studies have been done, the benefit is usually no greater than for a placebo (ie a treatment known to have no clinical effect).