Back pain and leg pain (sciatica)

Causes of Low Back Problems:

Most episodes of back pain can be classified as one of the following:

  1. Non-specific low back pain
  2. Discogenic pain (pain arising from the disc)
  3. Disc protrusion (this more typically causes pain in the leg)
  4. Facet joint arthritis and Spinal Stenosis
  5. Spondylolysis/Spondylolisthesis


  • Cancer and other tumours. See 4c
  • Spinal Infection See 4d
  • Inflammatory causes, such as rheumatoid arthritis or ankylosing spondylitis. See 4e
  • Fractures and injuries See 4f
  • Osteoporosis See 4g

4b(i) Non-Specific Low Back Pain

Low back pain is extremely common. The vast majority of adults will experience one or more episodes of acute low back pain at some stage during their life. The symptoms are not infrequent in childhood but much more common in adults and almost ubiquitous in the elderly. The symptoms vary from a mild ache after activity, which many would assume is muscular discomfort, to the devastating pain following a fracture or collapse of the vertebra.

Back pain can vary from a minor ache and discomfort after exercise to a serious and crippling disease. It can have a devastating impact on individuals and their families, destroying confidence and careers often for no good reason. Sciatica is the term given to pain in the leg usually arising from compression or irritation of a nerve in the spine. Back pain and sciatica are related but distinct. Nerve root compression causing sciatica is treated quite differently to back pain.

The first episode of acute low back pain in a previously healthy individual can be a frightening experience. From being fit and healthy one minute, a minor injury can suddenly result in severe pain and dependency on others. Patients often develop irrational fears. They may think that they are likely to become paralysed or have cancer in the spine. Fortunately, these conditions are rare. They may fear the loss of ability or even career. The vast majority of people should have no such fear. We hope that these articles will give an insight into what might be causing your problem and some clues as to what to do about it.

There is also information about the more serious aspects of back problems and a section on treatment for these conditions.

Back pain can be classified in a number of ways. One commonly used division is into two groups of acute low back pain or chronic low back pain. Acute low back pain describes the sudden onset of pain in a patient with no previous history of low back pain. The vast majority of episodes of acute low back pain resolve within 1 to 6 weeks. A few patients have severe pain for more than six weeks. Chronic low back pain is the label given to the condition when the pain has persisted for more than three months. Many patients with chronic low back pain report pain going on for years with fluctuating levels of symptoms.

Of course it is not always as simple as this and a more common situation is of acute recurrent episodes of low back pain. The patient may have severe pain, which often lasts for a few days or weeks and then settles almost completely only to return again. This cycle may repeat itself with monotonous regularity. The episodes often seem to be precipitated by minor movement or activity and, not surprisingly, patients attempt to avoid any activity that could aggravate the problem. This can lead to de-conditioning of the muscles and a decline in general fitness. These factors themselves may contribute to the ongoing problem.

4b(ii) Discogenic Pain

The nucleus pulposus
Fig. 06

Just as we get wrinkles on our faces, our discs degenerate as we get older. This is a normal process but it can lead to problems. The disc is made of outer tough fibres. This outer part of the disc is called the annulus or annulus fibrosus. The centre of the disc in young people is of soft jelly-like material called the nucleus pulposus or nucleus (see fig. 6). As we age, changes occur to both of these structures. The chemicals deteriorate. They are important for maintaining the high concentration of water within the disc. As the chemicals change, the water is lost and the discs become more brittle. The fibres of the annulus can then tear (annular tear). The tear may become inflamed and therefore painful. An annular tear will often cause back pain which may be central or to either side.

4b(iii)Disc Protrusion and Sciatica

Other terms for Disc Protrusion include: Acute Disc Herniation / Prolapsed Disc / Slipped Disc / Ruptured Disc)

For a patient developing sciatica, there is often a period of severe back pain which precedes the onset of the sciatica. The soft central part of the disc, the nucleus pulposus, may rupture through the outer layers of the disc (annulus fibrosus). If the fragment of nucleus compresses or irritates a nerve root, the patient will experience sciatica. The back pain may be relieved as the leg pain develops. Further damage to the nerve can cause numbness and weakness or partial paralysis. The pattern of these symptoms will often indicate which nerve is being compressed. The commonest discs to prolapse are the L4/5 and the L5/S1 discs.

A fairly accurate assessment of the likely site of the disc protrusion can be obtained from the symptoms and signs of the problem. This will depend on which nerve root is involved by pressure from the disc protrusion. A disc prolapse at L5/S1 usually causes pressure on the S1 nerve root. Fig 2. A disc prolapse at L4/5 usually causes pressure on the L5 nerve root.

MRI image taken from a patient suffering from severe left sciatica
Fig. 07

Fig. 07: This MRI image was taken from a patient suffering from severe left sciatica (pain to the leg) The picture is an axial image – a cross section – it is taken with the patient lying on his/her back and as though looking from the feet upwards. The image shows a large disc protrusion (red arrow) within the canal and displacing the left S1 nerve root (blue arrow). The protrusion is in the common postero-lateral position.

Disc protrusions can be described according to their position.

A disc protrusion compressing the central part of the canal is called a central disc protrusion.

The more common variety is the postero-lateral protrusion.

Occasionally the protrusion can lie outside the neural canal, in which case it is called a far lateral disc protrusion (Fig 8.). This tends to occur in older patients and at higher discs in the lumbar spine.

Far lateral disc prolapse
Fig. 08

Fig. 08: Far lateral disc prolapse. The prolapse lies in the more uncommon area outside the neural canal. This image is taken at the L5/S1 level but here the L5 nerve root is compressed. The red arrow shows the prolapse outside the canal compressing the Left L5 nerve root. The right L5 nerve root is shown (black arrow).

The size of a disc protrusion can vary enormously. The symptoms it causes can also vary enormously. Thus a small disc protrusion in a patient who has a narrow neural canal can cause devastating symptoms. A fairly large disc protrusion in a patient with a capacious canal can sometimes cause little trouble at all. It is not uncommon for a patient to have a scan to investigate one pain in the back and to find several other disc protrusions, which are causing little trouble.

This condition is commonest in patients in their thirties and forties. The condition can occur at any age but is rare in children, and extremely rare in younger children. A large disc prolapse in the centre of the canal can cause cauda equina syndrome. (See below).

Cauda Equina Syndrome

Fortunately, this is a fairly rare condition. When it occurs, it may be due to a huge disc protrusion. The spinal cord lies within the neural canal and finishes at the L1/2 level. Here it breaks up into series of nerve roots. Early anatomists felt these looked like the hair of a horse’s tail and therefore gave them the name “cauda equinae”. Pressure on these nerves can cause a cauda equina syndrome (CES). Cauda equina syndrome can be defined as a condition that occurs as a result of compression of more than one of the nerve roots making up the cauda equinae. It is often accompanied by urinary or bowel disturbance. These nerve roots supply the muscles that give power to the legs, sensation to the legs and genitalia and some of the nerves that control the function of the bladder or the bowels. A complete cauda equina syndrome can therefore be a devastating illness, which can render a patient paralysed from the waist down with no sensation to the legs and a loss of ability to control the bladder or bowels. A patient presenting with a CES should therefore be treated as an emergency in hospital. Patients suspected of having this condition should have emergency investigations, including an MRI scan.

The commonest cause of a CES is a large, sequestrated or central disc prolapse in the lumbar spine. Other conditions that can cause this problem include infection in the spine, tumours or fractures of the spine.

4b(iv) Facet joint arthritis and Spinal Stenosis

Arthritic facet joints
Fig. 09

Osteoarthritis occurs in most joints. It is more common with age and in certain joints. Hips and big toes are joints commonly affected. In the spine, a pair of facet joints lie behind and to the side of the neural canal at each level. These are often affected by osteoarthritis. The process of arthritis in the facet joints may cause other problems, as they lie so close to the spine. Symptoms of facet joint arthritis are of back pain, which is often worse on standing and after prolonged rest. Activity usually helps. If the arthritic process causes a lot of swelling, the extra tissues may compress the spinal nerves. In this case, symptoms of spinal stenosis can develop. This problem generally causes low back pain and leg symptoms with standing and walking. Numbness develops in the buttocks and legs, which usually settles as the patient sits down or leans forwards. A classical symptom is of the patient finding they can ride a bike but they cannot walk. More often these days, the patient finds they cannot walk unaided but a supermarket trolley solves the problem.

Fig. 09: The facet joints are arthritic (red arrows). The spinal canal is reduced to a fraction of its normal size (yellow arrow) which is causing stenosis of the nerves with symptoms of back and leg pain with numbness to the legs.

4b(v) Spondylolysis/Spondylolisthesis


Spondylolysis is shown in the L5 pars
Fig. 10: A spondylolysis is shown in the L5 pars

This term is given to the condition where the pars intra-articularis, which is part of the back of each vertebra, is damaged. This is often thought to be due to a stress fracture and generally occurs in young adults. The condition may be dormant and cause little trouble throughout life, although it regularly presents with back pain in a teenager or young adult. The condition is more common in sportsmen and women. Gymnasts and fast bowlers in cricket are two groups of athletes identified as being at risk. The condition is not seen in very young children. The condition becomes progressively more common throughout the teenage years until it reaches the level of approximately 6%, which is the incidence of this condition found in adults. Spondylosis has genetic factors. The condition can run in families and is extremely common in Eskimos. Some cases of spondylolysis progress to a spondylolisthesis.

This is a term given to the condition whereby the body of one vertebra slips forwards on the body of the vertebra beneath it. The slip can be mild or it can be extreme. Spondylolisthesis is classified according to the degree of slip. Thus a slip from 0-25% is classified as a grade 1 slip, a slip from 25-50% is classified as a grade 2 slip, a slip from 50-75% is classified as a grade 3 slip, a slip from 75-100% is classified as a grade 4 slip. If the vertebra slips completely off the one below then this is termed a spondyloptosis, or grade 5 spondylolisthesis.

Spondylolisthesis can be classified according to the cause of the slip. The causes include:

Spondylolisthesis L4/5
Fig. 11: Spondylolisthesis L4/5. The L4 vertebra has slipped forwards on the L5 vertebra. A pars defect is easily visible (red arrow) in the back of L4 which has allowed the slip.
  • Dysplastic
    This occurs if there is a congenital abnormality of the posterior spine, which allows the deformity to develop.
  • Lytic spondylolisthesis
    This is a spondylolisthesis that occurs in a vertebra previously affected by a spondylolysis (see above).
  • Degenerative
    This is an increasingly common cause of spondylolisthesis due to an increasing number of elderly patients in the population. The spondylolisthesis in this condition rarely spreads beyond a grade 1 spondylolisthesis. Most patients with this condition suffer from extensive degenerative disease and osteoarthritis of the spine.
  • Post-traumatic
    A spondylolisthesis can occur if a fracture of the neck of the spine through the pars intra-articularis has occurred.
  • Iatrogenic
    This condition means it has occurred as a result of medical intervention. The condition occurs in patients who have had posterior spinal surgery in the past. Excess bone may have been removed from the back of the spine, which can render it weakened. This can allow the vertebra to slip forwards.


Some patients with spondylolisthesis can have no symptoms at all. Occasionally patients present with the deformity. In children the abdomen can appear protuberant and an odd stance is adopted. Backache and back pain are common with the condition. Compression of the nerve roots can often cause sciatica in one or both legs. As patients age, further slip may occur and patients often present in middle age with back pain and bilateral sciatica due to an increase in the spondylolisthesis. They present at this age because the spine has slipped further forwards due to further degeneration occurring with the ageing process.

We specialise in assessment and diagnosis of spinal complaints with appropriate conservative treatment, planning surgery only when all other options have been exhausted.