The discs in the spine are the soft tissue structures that lie between the bones (vertebral bodies). They function as both a spacer and a shock absorber. A disc is made up of a ring of outer fibres (the annulus), and central jelly-like substance (the nucleus). As a disc ages, the outer ring of fibres weakens and the nucleus dries out. This results in a weaker disc that is more prone to injury. A number of factors are thought to influence the rate of disc degeneration including inherited factors, previous injury, heavy occupations, and smoking. The annulus may eventually rupture allowing the nucleus to prolapse through it. This is a disc prolapse. A disc prolapse is also known as a disc herniation, a slipped disc, a disc bulge, or a ruptured disc.

Disc prolapses can irritate the nerve root that passes in behind the disc in the spinal canal. This nerve root irritation occurs either by direct pressure of the prolapsed material on the nerve root, or by noxious inflammation due to chemicals released from the injured disc. This nerve irritation stops the nerve from functioning normally and can cause leg pain, numbness, pins and needles, and weakness. It may be associated with back pain.

The leg pain radiates in the distribution of the nerve that is being irritated. This is typically referred to as ‘sciatica’. Sciatica is pain within the distribution of the sciatic nerve. The sciatic nerve is formed from the nerves that emerge from the spine in the lower back. The distribution of the symptoms depends on which nerve root is being irritated in the lower back. A fairly accurate assessment of the likely site of the disc protrusion can be obtained from the clinical signs and symptoms.

The Natural History of a Disc Prolapse

Disc prolapses and sciatica are very common. A disc prolapse may occur without experiencing symptoms of sciatica. When sciatica does occur, it tends to be a sudden onset, severe pain. Over the first few weeks this pain may resolve completely or settle down and plateau at a more manageable level. In many cases the sciatica completely resolves without treatment. However, treatment may hasten recovery or at least help to ease the symptoms.

Symptoms that have been present for only a short period of time are most likely to spontaneously resolve. If they have been present for more than six weeks then the likelihood of rapid resolution becomes much less. If the symptoms recur, then it is likely that there will be further recurrences.

Cauda Equina Syndrome

The cauda equina (which is Latin for “horse’s tail”) are the nerve fibres in the lower part of the spine that supply the pelvis and legs. It is a continuation of the spinal cord. These nerves can become severely compressed if there is a very large disc prolapse. This causes a distinctive pattern of symptoms. This is called cauda equina syndrome.

Cauda equina syndrome typically presents as acute onset low back pain, pain in one / both legs, and numbness or tingling between the legs. There can also be an acute disturbance of your bladder or bowel function. You need to seek urgent medical attention if you develop numbness or tingling between your legs, feel the need to urinate, but cannot go, or if you loose control of your bladder or bowels. Cauda equina syndrome is an emergency. If the pressure on the nerves is not relieved then there can be permanent nerve damage affecting leg, bladder and bowel function. If cauda equina syndrome is diagnosed then it is a surgical emergency.

Assessment of Sciatica

Sciatica is assessed by taking a detailed history of your symptoms, followed by a physical examination. The history will include questions about the onset of symptoms, as well as the current level of symptoms. It is normal to be asked about your bladder and bowel function. This enquiry relates to loss of control rather than change in regularity. It is not uncommon for patients taking painkillers to become constipated, and for patients with back pain to need to go to the loo more frequently. There should also be questions aimed at excluding other causes of your symptoms. You will also be asked about other medical problems, medications that you are taking, whether or not you have any allergies, and if you smoke.

The examination will include checking your legs for strength and sensation, as well as assessing your reflexes. If there are any concerns about loss of control of bladder or bowel function, then it may be necessary to perform a rectal examination.

Whilst the history and examination findings are frequently suggestive of a diagnosis, in any patient in whom treatment is being considered this diagnosis needs to be confirmed by an MRI scan.

Treatment Options

Non-Operative Treatment

Most patients with sciatica crave effective pain relief. Simple painkillers (paracetamol/codydramol) and anti-inflammatory tablets (ibuprofen/naproxen) are the most commonly prescribed, though stronger, opioid-based painkillers may be required (codeine phosphate/dihydrocodeine/tramadol). Patients with intense nerve type pain may also respond to medications that specifically act to reduce the sensitivity of the nerves (gabapentin/pregabalin). 

During the very severe phase of sciatica rest may be necessary, though generally activity should be encouraged.

Physiotherapy / osteopathy / chiropractic treatment may be beneficial, but may also aggravate symptoms. Other simple interventions such as massage and heat may also help. A large proportion of patients who have suffered an acute attack of sciatica will start to improve after a couple of weeks.

Therapeutic Injections

An injection of steroid and local anaesthetic around the nerves aims to reduce the inflammation in the nerves, allowing the symptoms to settle down. The injection would be either a caudal epidural or a nerve root block, or both depending on the site of the disc prolapse. These injections are not effective in all patients. Your response to the injection determines what further treatment you will be offered: if you have complete relief then you will need no further treatment; if you have relief for several months before a gradual return of your symptoms then the injection can be repeated; if you have no relief or short lasting relief then we need to consider other options.

Surgery

The final option is surgery. This is usually an operation called a ‘microdiscectomy’. This is indicated in patients who have persisting pain not relieved by rest or injections, or who develop progressive neurological signs and symptoms, such as weakness and numbness.

What to do once you are Better

Once your sciatica has resolved you must continue to look after your back. The fact that you have had a disc prolapse does not preclude a normal lifestyle. However, we would recommend that you:

Exercise: Undertaking an exercise program that aims to improve and maintain aerobic fitness is important. This may include regular brisk walking, swimming or cycling. Specific exercises to maintain flexibility and strengthen the abdominal and spinal muscles are important.

Avoid smoking: Smoking is associated with increased back pain and poorer outcomes from spinal surgery.

Avoid obesity: Being overweight forces the spine to carry unnecessary loads, and is associated with back pain.

Avoid heavy lifting: Patients who have had spinal problems should be cautious with heavy lifting and prolonged manual work, as this may cause a recurrent disc prolapse or further back injury.