Patient Information Sheet : Spinal injections - Lumbar Epidural

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What Is It?

An injection into the spinal canal can either be around the dura (epidural injection) or into the dura (intradural injection). Intradural injections are used when obtaining samples of cerebro-spinal fluid when conditions such as meningitis are suspected or for diagnosis of other conditions such as MS (Multiple Sclerosis). It is also administered to give anaesthetics, usually for lower limb operations such as hip or knee replacements (spinal anaesthetics). An extradural injection is used by spinal surgeons to give drugs for the treatment of spinal disease directly into the damaged area rather than use the same drugs by mouth. Drugs injected into the epidural space travel a few centimetres up and down the spinal canal and bathe the contents of the spinal canal, i.e. the dura and nerve roots, the intervertebral discs and the facet joints (see diagram).

DIAGRAM OF A LUMBAR VERTEBRA

Spinal injections include facet joint injections where the surgeon tries to inject directly into the facet joints (rather than around the facet joints as in an epidural injection). This usually involves a very fine needle placed under xray control to ensure that the point of the needle is actually within the facet joint. A similar injection is also known as a nerve root block where an injection is given under xray control with a very fine needle. The aim of this injection is to get the point of the needle into the sheath surrounding the nerve root at a particular level and perform a nerve root block, anaesthetising just the nerve root and this is often used for both diagnosis and treatment. Both facet joint injections and nerve root blocks tend to be used when there is some diagnostic doubt regarding the nature and cause of any back pain and symptoms. These injections are used more by pain relief specialists rather than spinal surgeons, although there is a degree of overlap.

The Procedure: Lumbar Epidural

I give the injection under local anaesthetic but it is advisable that the injections are carried out in hospital as part of an operating theatre list. Occasionally a spinal anaesthetic will result from the injection rather than the intended epidural injection (see complications below). Injecting into the epidural space can be done in one of two ways. I anaesthetise the skin, in the mid lumbar spine at the lower part of the back with the patient sitting up, facing away from me. An alternative route is to inject at the very tail end of the spine (a caudal injection) which is given into the crease between the buttocks at the tip of the spine. In this case the patient either lies face down or lies on their side, with their knees and hips bent upwards.

The route of the injection (lumbar and caudal) depends on your surgeon’s preference and training. I will then use a slightly larger needle to go through the numb area in between the bones of the spine until I am in the epidural space. I can tell when I am in the correct area by feel and experience. Once in the right space (in the spinal canal but not in the dura) I will then inject a combination of local anaesthetic (to numb rather than block the nerves) and steroid (usually a long acting steroid such as Lederspan, Adcortyl or Depomedrone). The aim of the steroid or cortisone injection is to allow a reduction in any inflammation and irritability of the tissues in the spinal canal, i.e. facet joints, degenerative discs or inflamed nerves. The cortisone works over the next few weeks and often improves symptoms sufficiently to allow an individual to return to more normal activities.

Once the injection has been completed (involving around 10 mls of injection fluid) the needle is withdrawn and a simple Elastoplast is put over the puncture wound. The patient is then monitored for 15 – 20 minutes to ensure there is no undue reaction to the injection contents such as an allergic response or fainting and also to ensure that the injection has not inadvertently been given into the dura, which will give a spinal anaesthetic. This is not usually a problem in that the local anaesthetic will wear off within a few hours but it may mean that the patient has to stay in bed and under observation for a few hours until the local anaesthetic wears off. This is why it is recommended that these injections be undertaken in theatre and as part of a normal operating list so that the facilities are available to monitor the patient after the injection.

In 99 times out of 100, there are no significant reactions to the injection and following a period of observation for 15-20 minutes the patient is encouraged to mobilise and walk around the ward. Once safe and comfortable the patient is allowed home, usually within an hour or two of the injection. The patient is advised not to drive for at least 24 hours following the injection and to be taken home and accompanied for the first 24 hours by a friend or partner.

What Can Go Wrong?

The injection is usually very safe. The main complication is that the injection does not work and in around 50% of patients the epidural makes little if any difference to the overall symptoms. It is very unlikely that patients can be made worse by the injection. However, significant complications can occur, for instance the injection into nerve tissue can damage that tissue causing an area of weakness or paralysis which can be permanent, but such a complication is incredibly rare, certainly less than 1 in 1,000. The injection can cause bleeding if the needle punctures a vein in the spinal canal. In theory the bleeding could cause a significant blood clot to form with a subsequent rise in pressure in the spinal canal. This can lead to disruption of nerve function and may even require surgical decompression by open operation for relief of the pressure (cauda equina syndrome). Again this is very rare, less than 1 in 1,000. More common, but still rare, is that the injection is given into the spinal coverings (intradural) and causes a spinal anaesthetic as detailed above. This happens in around 1 in 100 cases.

What Happens After Discharge?

Following the injection, I will normally arrange to see you in clinic around two-three months after the injection. As noted above the injection has two components – a local anaesthetic to try and reduce pain and discomfort in the short term, i.e. the first few hours-days, and steroid to reduce inflammation and swelling over a period of weeks and therefore I will wait two-three months to assess the effect if any of the epidural injection. Around 50% of individuals who undergo an epidural injection have significant relief of symptoms. However, it is unusual for the epidural to cure a patient’s condition. More likely is that the epidural helps to speed up the normal recovery process and allows an individual to return to more normal activities sooner than they would otherwise have been able to. It is therefore a treatment rather than a cure.

After two-three months, when reviewed in clinic, if the epidural has provided no relief at all or the epidural has relieved symptoms sufficiently to require no further treatment, then no further epidurals will be required. Occasionally the epidural improves symptoms significantly but they are still at a level which is intrusive and therefore a second or even third epidural will be considered. Epidural injections can be given up to three times in a series of injections over a course of three-six months but one would normally hope not to undertake these injections more often than three times in any one year. Steroids can alter tissue characteristics, in particular they can weaken the ligaments and joint linings and if used excessively can lead to premature wear and tear changes in the spinal tissue.