Sciatica is a common and often disabling condition. It has an annual incidence of 1-5%, and a lifetime incidence of 15-40%. There is no sex difference, is rare under the age of 20 and peaks in the 5th decade. Sciatica can be a misleading term to both doctors and patients, often being used to describe any type of pain that occurs in the back, buttock or leg.
The sciatic nerve is formed by the confluence of the L4 to the S3 nerve roots. It courses through the back, pelvis, buttock and into the posterior aspect of the thigh. By definition sciatica is caused by any irritation of the sciatic nerve or its roots. This occurs most commonly in the lower back secondary to a lumbar disc prolapse, but may occur anywhere along its pathway. The L5/S1 disc is most commonly affected followed by the L4/L5 disc. The pain in sciatica may be attributed to either mechanical compression or chemical inflammation of the nerve root. Mechanical compression is more likely to cause loss of neurological function. Other potential sites of nerve compression are in the pelvis, gluteal musculature and upper hamstring.
It is important to consider other causes of buttock and leg pain that may mimic, but are not true sciatica. These may include hamstring origin tendinopathy, gluteal tendinopathy/bursitis, lumbar referred pain, hip joint pathology or sacroiliac joint dysfunction.
Historically sciatic pain radiates from the buttock, into the posterior thigh, calf, lateral shin and into the foot. There may be associated para or dysaesthesia. It may or may not be associated with a definite episode, injury or even back pain. It may occur after a lifting incident, although sometimes with a minor movement such as picking up an item off the floor. Pain may be aggravated by sitting, bending, coughing, sneezing or lifting. Symptoms of a cauda equina syndrome such as loss of bowel and bladder function need to be excluded as they constitute a surgical emergency.
Clinically the patient may demonstrate a protective list away from the side of the pain. A detailed assessment will include a full neurological examination, including power, sensation and reflexes. This includes plantar reflexes. Both myotomal and dermatomal abnormalities should be considered. Restriction of lumbar motion with reproduction of radicular pain may occur. The patient should be asked to stand on their toes, heels and squat. Signs of neural irritation, including the slump test and straight leg raise test should be performed. Straight leg raise will generally be limited to between 30 to 60 degrees. Positive cross-over signs (reproduction of pain on passive extension of the contra-lateral leg) are strongly suggestive of true sciatica and generally an indication of a large disc prolapse. Lumbar palpation may not reveal much abnormality. The finding of true neurological loss is a key clinical finding. A thorough examination should include the hip joint, gluteal and hamstring tendons and the SIJ.
True sciatica will often be a clinical diagnosis. The natural history is normally favorable, so initial investigation is not always warranted. Imaging may be required if symptoms are not settling, there is worsening neurological function or interventional treatments are being considered. MRI scanning is the gold standard, but a CT scan is a viable alternative if there are issues obtaining an MRI.
As mentioned before, the natural history of sciatica is favorable, with 80-90% of patients settling within a 3 month period with conservative therapy alone. This may include anti-inflammatory medications, physiotherapy and avoiding aggravating activity. Physiotherapy should include a combination of manual or ‘hands on’ therapy, exercise prescription and lumbar traction. Important exercises should include McKenzie extensions and core strengthening. Patients should be counselled to avoid lifting and positions that aggravate their pain (usually prolonged sitting or bending forward).
Ongoing symptoms may require interventional treatments. A CT guided peri-radicular nerve root injection has a 50% chance of improving pain in sciatica. A partial discectomy may be considered if there is severe and unremitting pain or if there is deterioration of neurological function.
- Sciatica is a relatively common condition
- ‘True’ sciatica needs to be differentiated from other causes of buttock and leg pain
- The natural history is favorable for resolution within 2-3 months
- Conservative treatment includes rest, anti-inflammatory measures, physiotherapy and possible use of peri-radicular cortisone injections
- Surgery is indicated for intractable pain or worsening neurological function