Family doctor

DEFINITION OF SCIATICA

Sciatica is pain within the pathway and distribution of the sciatic nerve. The sciatic nerve is formed by nerves from the spine at the junction of the lumbar and sacral regions. The nerve passes from the spine into the pelvis then into the buttock, posterior (back of) thigh and down below the knee.

Below the knee the nerve divides into two branches, one going through the posterior (back) calf down the inner side of the ankle, and a second division goes through the outer side of the calf around the top of the ankle and foot to the toes. The important features of sciatic pain are that it goes below the knee, and it is associated with neurological symptoms. The neurological symptoms include a sharp or burning character to the pain; changes in sensation such as tingling, pins and needles or numbness; and association with weakness.

The branches of nerves from the spine that make up the sciatic nerve are the low lumbar and upper sacral nerves. These branches give sensation to the front, the outside and the posterior (back) part of the leg below the knee. They also give strength to the muscles that pull up the ankle and the toes, turn the foot to the outside and give strength to the calf muscles.

The nerve roots involved also supply the ankle reflex. The most common nerve roots that are involved in sciatica are the L5 (Fifth Lumbar) nerve root and the S1 (First Sacral) nerve root. These differing nerve distributions result in differing areas of numbness and weakness. The L5 nerve root (so named because its origin is from the lower part of the 5th lumbar vertebra) is often associated with numbness that goes through the top of the foot to the great toe.

The S1 nerve root (named because it exits the spine below the first sacral vertebral segment) is associated with sensation that goes through the outer aspect of the foot to the little toe. Loss of function of the S1 root will be associated with numbness in this area.

It is important to understand that sciatica is pain that goes through the course of the sciatic nerve and this means that it should go below the knee. Many people mistake buttock pain for sciatica. It is true that the sciatic nerve goes through the buttock but many other causes of pain from the spine may be referred to the buttock and the presence of pain in the buttock alone does not imply irritation, inflammation or compression of the sciatic nerve.

CAUSES OF SCIATICA

Pain that occurs within the distribution and path of the sciatic nerve is most frequently due to compression of the nerve within the spinal canal. This most commonly occurs secondary to disc herniation in the middle years from 20 through to 60. In older age groups it may occur secondary to narrowing of the path for the nerve ways (spinal stenosis).

There are many other causes of sciatica. Potentially any injury or abnormal process that involves the sciatic nerve may cause sciatica. In practice the commonest cause of sciatica is disc herniation.

DISC HERNIATION

The discs in the lumbar spine are the soft tissue structures that lie between the vertebrae. A disc consists of an outer casing or annulus, and an inner jelly-like substance or nucleus. The healthy disc has a jelly-like nucleus, but as discs age or have been subject to damage and/or prolapse, the healthy jelly dries out to have more of a consistency of crab meat. A disc herniation occurs when the wall of the disc or annulus develops a tear or weakness and disc material comprising nucleus and annulus is pushed out through the weakening in the outer annulus. This may be associated with local back pain related to the damage to the annulus.

When the disc herniates or ruptures it frequently puts pressure on the nerve root that passes in close to the disc in the spinal canal. This is where the symptoms of sciatica may occur. Most discs that rupture develop changes in the disc material consistent with degeneration or wear and tear. It is not entirely clear whether this occurs before the disc ruptures or after it. It seems likely that a variety of possibilities exist. The disc annulus may weaken and develop tears with age, but it also seems likely that injury may have a role.

Newer evidence suggests that some groups of patients may have abnormalities in the tissue makeup of the disc that predispose them to rupture or weakening of the outer annulus or casing.

When the nerve passing the disc is exposed to a rupture, the nerve can either be affected by direct pressure of the prolapse or by chemical inflammation caused by the tissue from the disc. Direct pressure occurs when the nerve is trapped by a prolapse within the nerve canal. This probably accounts for changes in nerve conduction which the patient feels as altered feeling or muscle weakness. The other effect that the disc prolapse can have is to inflame the nerve. There is now good evidence that the chemicals from the nucleus can leak out of the prolapse onto the nerve root resulting in inflammation of the nerve, pain within its distribution (sciatica) and also changes of nerve function (again manifest by numbness, pins and needles or weakness).

INCIDENCE

As most patients with back problems find, these are exceptionally common. It is often stated that 80% of adults will experience severe back problems at some stage of their life. It is also stated that 20% people may have significant back symptoms in the current year. Back pain is much more common than sciatica, but bouts of sciatica are also exceptionally common and many people experience these. It has also been discovered, with the use of new scanning techniques, that many disc herniations occur without giving the patient pain or indeed any awareness of the problem. Scans on people with no symptoms at all have shown that many will have disc herniations. It is unclear why some patients are extremely troubled by disc herniation causing sciatica, and other patients do not have symptoms.

NATURAL HISTORY OF SCIATICA

As stated above, disc herniation and sciatica are very common. Patients may have disc prolapse without symptoms of sciatica. When sciatica does occur, it tends to be associated with an early, intense phase of severe pain which is probably due to both pressure and inflammation secondary to disc herniation. The pain often settles after the first few weeks. It may resolve completely or plateau at a level less severe than when it was most intense, but still giving ongoing pain. Some have suggested that the early intense pain correlates with inflammation and the latter pain with ongoing pressure. The natural history of any condition is the description of events that occur if no treatment is instituted. We believe that many bouts of sciatica resolve without treatment. Treatment may hasten resolution or ameliorate symptoms at the time. If sciatica occurs and has been present for a short duration of time it is more likely to spontaneously resolve. If it has been present for a long period of time it becomes much less likely to resolve. If it has resolved and recurs particularly more than once, then it is more likely that further recurrences will occur and treatment will eventually be necessary.

As a guideline, if the sciatica has been present for less than four weeks there is still a reasonable chance that it may resolve. If it has been present for more than six weeks the likelihood of rapid resolution becomes much less.

EVALUATION OF SCIATICA

When a patient sees the doctor for symptoms of sciatica, detailed evaluation is required. This normally consists of a detailed history of symptoms and events that led to the onset of them. It should also include a systemic questioning to exclude other potential causes of problems.

History is then followed by an examination which aims to exclude other causes of leg pain and document any evidence of tension on the nerve, tenderness to the spine and neurological change in the sciatic nerve distribution.

This will include a neurological examination of the legs checking for sensation, strength and any change in reflexes. It is very common for the doctor to ask about symptoms relating to abnormal function of the bladder or bowel.

This inquiry relates to symptoms of loss of control of the bladder or bowel rather than change in regularity. If there are symptoms related to loss of bladder or bowel control the doctor may have to perform a rectal examination where the back passage is checked for any loss of sensation or anal muscle strength.

It is not uncommon for patients who have pain or who are taking pain relieving medication to become constipated or find that they are inhibited from straining on the toilet. It is also not uncommon for patients with back pain to go to the toilet more frequently. The doctor asks about symptoms of control loss because there are very rare cases where large disc herniations put pressure on the nerves supplying the bladder and bowel. If this should happen and there were permanent damage to these nerves, it might result in permanent loss of control of bladder and bowel function. This has very important social as well as medical consequences.

Most often the diagnosis of sciatica is based on the history and examination findings. X-rays may be performed. Most often an x-ray will not give an obvious clue as to the cause of the sciatica. It is performed to exclude some of the rarer causes including infection or tumour. Many researchers have found that the routine use of x-rays for early symptoms is unwarranted.

They have suggested that x-rays should be withheld until the six week stage if symptoms have not resolved. If there is any suspicion of other possible cause of sciatica, such as a past history of cancer, the doctor will tend to move to x-rays earlier.

The newer investigations include CT and MRI scan. These scans demonstrate the disc in detail, and the MRI scan will also demonstrate the nerves.

They show the disc herniation. The use of such scans has become much more common. Normally it is a final step before considering surgical intervention.

TREATMENT OPTIONS - NON SURGICAL CARE

Most patients desire relief from pain when they have severe sciatica. This can be achieved using a number of medications. Simple pain killers and anti-inflammatory medications are most commonly prescribed. These can be used together. Anti-inflammatories can be very useful although care must be taken if there is a history of peptic ulcer disease or other gastrointestinal upset, or any history of poor kidney function.

Stronger pain relievers, some with an opioid base, may be used for more severe and persistent pain. Patients with intense neuralgic or nerve type pain may also respond to medications that specifically act to reduce the sensitivity of the nerves. These include low-dose antidepressants (tricyclics) and other drugs of a sedative nature. During the very severe phase of sciatica rest may be necessary. There is a growing trend to avoid prolonged periods of rest unless absolutely essential. Many find that it is the only way that the very severest of symptoms can be controlled.

Physiotherapy may have a role, although with severe sciatica it can sometimes upset symptoms. Simple interventions such as massage and heat may help relieve symptoms but have not been proven to effect the outcome.

Other physical therapy interventions such as the McKenzie technique may have a role when provided by experienced practitioners.

Epidural injections of steroid may also be used. This is a technique where cortisone/steroid preparations are injected around the nerves in the spinal canal. The aim of the injection is to reduce the inflammation around the nerve root. This technique may be very effective but is somewhat unpredictable. In some patients it is not beneficial. The risks are relatively low. It remains controversial as to whether or not this option has a role.

All patients who are being cared for with sciatica should be encouraged to maintain activity. This represents part of the swing away from bed rest mentioned before. It is clearly better if patients can maintain function and employment if possible even when symptoms persist. Many patients take the view that they should rest and should not overdo it at this stage.

The medical evidence does not support extreme activity restriction. The role of other physical therapy such as chiropractic or osteopathic manipulation for sciatica remains unclear.

Sometimes patients get relief from this but there is also the risk that pressure on a nerve may be exacerbated by manipulation. It is not unknown to see patients who develop sciatica after manipulation of the spine.

SURGICAL OPTIONS FOR SCIATICA

If sciatica has been present for a prolonged period of time (over six weeks) and has failed to respond to conservative care, surgical treatment may have a role. It is imperative that in this situation the patient is investigated with a CT or MRI scan to demonstrate the disc herniation. At this point surgical treatment may be offered. The commonest and most effective treatment is partial excision of the disc and is normally referred to as "discectomy". This should only be considered for prolonged pain (greater than six weeks), pain within a sciatic distribution below the knee, pain associated with some form of neurological symptom and pain that is exacerbated by stretching the nerve. In these situations pain can most often be relieved with partial discectomy.

DISCECTOMY - THE PROCEDURE

Discectomy involves an operation on the low part of the spine done from a posterior surgical approach. Under anaesthetic the patient is placed prone and a longitudinal incision made over the relevant area of the spine. The muscles are separated so that the vertebra can be seen and then the soft linings on the back of the spinal canal are removed between the bony vertebrae. The nerves are inspected and moved to the side to allow the disc herniation pushing on them to be visualised. When the disc herniation is seen, it is removed, leaving the nerves free of pressure.

Many patients are concerned that the disc will be removed completely. This does not happen. The bulging portion of the annulus or outer casing of the disc is incised and it is removed. Free fragments of the disc core are also removed, but the remainder of the outer casing of the disc is left intact. This normally allows the nerve to lie freely without pressure and is associated with relief of sciatica. The incision that is made into the disc through its casing wall then scars over in the weeks subsequent to surgery.

All patients who have a discectomy are left with an abnormal disc, yet few suffer significant back pain.

The operation of discectomy in its various forms has been around for 70 years. The main features of the operation have not changed although many surgical modifications have been performed to make the incision smaller.

Along with this, the hospital stay has been reduced and an increased speed of rehabilitation has been observed. Many patients can get back to work within a couple of weeks from surgery although often with some restriction of activities.

RECOVERY FROM SURGERY

When standard discectomy is performed, most patients leave hospital 24-48 hours after surgery. The expectation is of relief of sciatica although there will be pain in the back from the surgical procedure.

Patients are encouraged to remain active at home and only rest for short periods as necessary. A walking programme is often useful. Theoretically sitting can be disadvantageous but in practical terms it must be achieved. Many patients find sitting the least comfortable position, yet despite this many are able to return to work and driving at 2-3 weeks.

Most patients are advised to limit activity to a walking programme through that period of time. This allows a return of general fitness along with improved movement of the trunk without stressing it. After the six week period patients are encouraged to increase activity.

Increasing walking along with a swimming programme can be useful. At the 12 week post-operative stage patients can further increase their activity. A programme at the gymnasium working on upper and lower body strength may be useful. Cycling can also be beneficial at this stage.

Return to other more aggressive activities is programmed in conjunction with the surgeon.

ALTERNATIVE SURGICAL TREATMENT

There has been much discussion in the media of alternative surgery.

There is always enthusiasm for percutaneous discectomy or laser assisted procedures. Many such procedures have been tried in the spine. There has been a wide expansion of equipment for such operations in the last few years. Unfortunately there is little doubt that most of these procedures are inferior to the traditional operation of discectomy. Part of the reason for this is that although the operation is called a discectomy, the focus is not so much on the disc, but on protection and decompression of the spinal nerve in the spinal canal. The modified operations mentioned above have focused on resection of tissue within the centre of the disc. This does not allow access to the nerve, yet it is the nerve that must be seen, protected and released.

There is good evidence that these newer procedures are inferior to traditional partial discectomy. The discectomy operation remains the gold standard.

Other alternatives to surgery have included injection of chemicals to shrink the centre of the disc so as to reduce the effects of the prolapse on the nerves. This treatment (chymopapain injection / chemonucleolysis) is not practised in New Zealand. It has been popular in other parts of the world, but has now faded from prominence. The treatment of chemonucleolysis is clearly better than no treatment, however it has not been able to match the success rates of standard discectomy.

REQUIREMENT FOR URGENT TREATMENT

As noted above, the situation where a large disc herniation puts pressure on the nerves to the bladder and bowel is an emergency. The consequences of this situation left untreated can be severely disabling.

All doctors are on the look out for this situation, and should this occur it requires urgent assessment and treatment. It is the sort of situation that is attended to acutely with urgent surgery. Delays of days can be very serious and result in permanent loss of function. Apart from this situation, most other cases of sciatica should be treated cautiously with an attempt to manage them non operatively. In some situations major muscle weakness may result in clinical syndromes of foot drop and severe limp. These are often treated more urgently although it is somewhat questionable whether early or urgent treatment is of great benefit.

COMPARISON OF SURGICAL OR NON SURGICAL TREATMENT FOR SCIATICA

Because sciatica presents with a variety of syndromes (in terms of intensity and duration of pain) the outcome and appropriate treatment options can be varied. Most authors would agree that short term sciatica without major neurological loss should be treated without operation. This involves activity modification and treatment of symptoms with analgesics. It is likely that many cases will settle down and if symptoms are resolving after 3-6 weeks, surgical treatment may not be required.

When symptoms have been present for a longer period of time, the likelihood of spontaneous resolution is less. It is clear that in this latter situation surgery offers a significant chance of rapidly improving symptoms. If surgery is not performed at this stage it is likely that gradual resolution will occur in the majority of patients. Unfortunately without surgery this resolution tends to be slow. Proponents of non operative treatment will argue that at time periods several years after the onset of sciatica, the pain relief will be the same in those who have had surgery as those who have not had surgery. It is clear that patients who have surgery have much earlier relief from pain, normally soon after the operation. Most patients far prefer the rapid resolution of pain particularly if it is severe.

It is also clear that the optimum time for surgical treatment includes a "golden window." Most patients who have marked sciatica secondary to disc herniation benefit from operation between six weeks and six months from onset. If pain is prolonged, it is likely that disability will also increase dramatically. In this situation, where a patient has had sciatica for perhaps years, the nerve probably undergoes changes which cannot be reversed. There is evidence of complex changes in the pathways of the nerve and spinal cord when there has been long term compression or stimulation of the nerve causing pain. In these situations late operation for sciatica is often associated with inferior outcomes. The dilemma for the patient is often whether or not to wait and see if the sciatica will resolve on its own without surgical treatment. A practical approach to this problem would be that if the pain is continuing to improve after the six weeks period then it seems that a wait and see approach is justified.

If, however, pain resolution is incomplete with significant residual symptoms, or if there are recurrences of severe pain, then it is much less likely that pain will resolve spontaneously. In that situation the history of surgical treatment would suggest that this may be a better option.

COMPLICATIONS OF SURGERY

In experienced surgical hands the risks of complications secondary to discectomy are low. As with all operations, discectomy is associated with the risk of infection, clots in the legs (DVT), and allergic reactions or anaesthetic complications. The risk of infection is less than 1% but when it occurs can be associated with infection in the disc space and this can be a serious complication. Treatment involves prolonged antibiotics. More commonly a superficial wound infection may occur and this resolves with a short course of antibiotics.

Because the disc is abnormal at the time of herniation and is not made normal by the operation of discectomy, residual back pain may occur. The incidence of severe back pain following discectomy is probably less than 10% and is most often managed conservatively. A small proportion of patients may come for further surgical treatment if severe back pain persists. This treatment may include spinal fusion although a detailed discussion of this is beyond the scope of this article.

A further complication that patients should be aware of is that of recurrence of disc herniation. In most articles the recurrence rate is about 5%. A further piece of disc material may escape through the area of previous disc rupture. This can occasionally occur soon after an operation and perhaps more commonly occurs some years later. The treatment for this is consideration of repeat discectomy if symptoms warrant, and if there is failure to respond to non operative care.

Repeat discectomy is a technically more difficult operation because of scar tissue. Expectation of outcome is somewhat more guarded than primary or first time discectomy.

Complications such as nerve damage are uncommon. Occasionally the lining to the nerve (the dura) can be torn. This can generally be repaired or patched and, apart from a short period of increased bed rest after operation, does not normally result in other complications. Major complications such as nerve damage resulting in major muscle weakness or paralysis are very uncommon. It is however not uncommon for patients to be left with persistent patchy numbness.

Once the nerve has been inflamed or compressed, the most sensitive function is that of sensation and this may not recover. Residual numbness is not uncommon. After surgery often the relief of pain is associated with more appreciation of numbness. This generally recovers and may do so for up to two years from surgery. Persistent numbness is not uncommon and seldom disabling if good pain relief has been achieved.

OUTCOMES FROM SURGERY

The majority of articles following up patients who have undergone discectomy for sciatica demonstrate major improvement in leg pain in 80%-90% cases. This normally occurs rapidly after surgery and is sustained. This is a considerable improvement upon the natural history of sciatica when patients have had prolonged symptoms.

ONGOING BACK CARE

When sciatica has resolved, whether or not surgery has been required, the patient should maintain optimum conditions for their spine. The fact that the spine has had a prolapse, and is not normal, does not preclude a relatively normal lifestyle.

General recommendations include avoidance of smoking (which is associated with increased back pain and poorer outcomes from spinal surgery), and avoidance of obesity (which is associated with greater loads across the spine and other joints).

An exercise programme to maintain aerobic fitness is to be encouraged. This may include regular brisk walking, swimming or cycling. Specific exercises to maintain flexibility and strengthen the abdominal and spinal muscles are important. These can be obtained from physical therapists with an interest in home based exercise programmes.

Finally, the patient who has had major spinal problems or surgery should be cautious with heavy lifting and prolonged manual work which may expose them to recurrence of prolapse or other back injury. This latter comment should not be interpreted as an instruction to "wrap themselves in cotton wool!" as too little activity is more of a danger than too much activity.