Disc Prolapse - Sciatica
Sciatica – this describes a characteristic pain felt in the lower back, buttocks and the posterior and lower leg. It results from compression of any of the 5 nerve roots that contribute to the sciatic nerves (L4-S3).
- The most commonly affect disc is at L5/S1, and will compress the S1 nerve root.
- L4/L5 pressing on L5 are the second most common types of problems
- In the cervical spine, herniation at C5/C6 is common
- Femoral Nerve – L2-L4 – Anterior compartment of thigh
- Sciatic Nerve – L4-S3 – Posterior compartment of thigh, plus the rest of the leg, including the foot
- Intervertebral discs consist of concentric collagenous fibres (the annulus fibrosis) surrounding a central nucleus (the nucleus pulposus) of degenerated collagen. The nucleus is generally softer than the annulus fibrosis.
- The discs contain a great deal of water, held in place in collagen molecules by electrostatic forces in special sidechains. As we age, the disc dehydrates, and loses vertical height.
- The cervical and lumbar discs in particular are prone to more severe / early degeneration.
Prolase of a disc occurs when there is a defect in the annulus fibrosis that allows the nucleus to herniate out. This can lead to compression of nerve roots.
- This most commonly occurs in the lumbar discs.
- At some point between the age of 25-50, the discs become gradually weakened and prone to prolapse
- Herniation usually occurs posteriorly, but can occur laterally
- In very rare cases, the disc can herniate into the vertebral bone itself, sometimes all the way through to the marrow. They can lead to necrosis of bone tissue, and inflammation. These herniations are called Schmorl’s nodes.
- Age increases the risk of herniation, due to dehydration of the disc
- Herniation often occurs as the result of strenuous physical activity involving the lumbar spine. The older you are, the less strenuous the activity needs to be to cause the herniation!
- Disc herniation is often asymptomatic
- Back pain – due to the disc pressing on the longitudinal ligament and dura mater. The pain usually presently acutely
- Buttock / leg pain – due to impingement on one of the nerve roots. The irritation of the nerve can be a combination of both physical pressure on the root, and chemical factors released.
- Altered sensation
- motor weakness
- altered reflexes
Localisation with symptoms
- L5/S1 disc – S1 nerve root – will cause symptoms from the buttocks to the foot, and particularly on the lateral side of the foot. There will be calf weakness, and altered ankle reflexes.
L4/L5 disc – L5 nerve root – pain radiating to the ankle and top of the foot sensory changes on the lateral side of the leg, and on top of the big toe.
- Both the above will result in a positive sciatic stretch test
Higher up lumbar discs – these are less common, but will cause anterior thigh pain, quadriceps weakness, and pain around the knee. The knee reflex will be altered.
- This will result in a positive femoral stretch test
However! – this is not always accurate. In 6% of cases, the herniation will occur laterally, and not posteriorly, and thus the exiting nerve, rather than the traversing nerve will be affected. E.g. a lateral herniation at L4/L5, will cause L4 symptoms.
- Lateral herniations tend to occur in older patients
- They can be very painful!
Is made on the basis of clinical signs
90% will resolve spontaneously – the herniatied material will become dehydrated, and be reabsorbed.
- When patients initially present, you should advise them to rest for a short period before returning to normal activities
- Any improvement of signs and symptoms is a good prognostic factor
- Advice analgesics and NSAID’s
- In more severe cases, physiotherapy may be beneficial
- In very severe cases, you can give local steroid injections, which will provide pain relief
In cases lasting longer than 12 weeks:
- Further investigation may be necessary
- X-ray is of virtually no use!
- MRI – is the investigation of choice. It can directly show the herniation, allowing you to assess its location, size, and view any impinged structures
- CT –may also be useful, but provides a lower resolution image, and has been mainly superceeded by MRI
- Operative treatment is given in some cases. The main procedure is called microdiscectomy. It is performed thrugh a small inscisional windows cut in the laminae and ligamentum flavum. In 90% of cases, patients can return to work within 6 weeks.
Complications – rare, but can include:
- Disc damage
- CSF leak
- Recurrent disc herniation
- Post-Op pain
Cauda Equina Syndrome (CES)
This is a SURGICAL EMERGENCY! it is usually the result of massive disc herniation, and many nerves can be compressed in the cauda equina. It usually occurs acutely, and there can be:
- Impaired sphincter responses (e.g. difficult micturating, post voidal incontinence)
- Altered perianal sensation (saddle anaesthesia)
- Decreased anal tone
- LMN signs in the lower limbs
Rapid imaging and surgical decompression are needed to maintain function. MRI is preffered, but CT can also be used to confirm the diagnosis.
Metastatic disease should be suspected in a patient with history of weight loss and CES
Prognosis – mainly depends upon the time the nerves were decompressed for. Some patients will have permanent damage, whilst others will regain varying degrees of function over varying timescales.
Differential Causes of Nerve Root compression