Sciatica is a term which we commonly associate with radiating pain down the back of the leg. The name sciatica comes from an irritation or injury to the sciatic nerve, which is the largest nerve exiting the lumbar spine and making its way down the back of the leg. Along with pain, there can also be neurological symptoms such as numbness, pins and needles and muscles weakness associated with this condition.
What are the common causes of sciatica?
- Compression from a disc protrusion contacting the sciatic nerve root.
- Disc protrusion near the sciatic nerve without contact on the nerve root. Here, inflammatory chemicals from the injury can act on the sheath of the nerve thereby stimulating it.
- Overactivity through the gluteal muscles compressing the sciatic nerve. This is commonly termed “piriformis syndrome”. There is some conjecture about whether this mechanism of compression can exist, and whether it is just referred symptoms from the lower back or gluteals (Stewart, 2003). Many believe that due to some anatomical variations in people that the sciatic nerve can sometimes be trapped as it passes through the piriformis muscle in the gluteals.
- Mechanical irritation of the sciatic nerve where the nerve passes out of the spinal column through openings called intervertebral foramina.
How do we know if it’s nerve pain or just a referred pain from the lower back?
Although there are exceptions to the rule, nerve pain is generally sharp, shooting and can be burning in nature. There can also be a combination of numbness, pins and needles and/or weakness in the muscles if the nerve is involved. True sciatic nerve pain will generally be felt below the knee. On the other hand, referred pain from the lower back or gluteals without nerve involvement, will present as a constant dull, diffuse ache. It will typically be felt in the gluteals and the pain will generally be felt above the knee.
The outlook is generally positive for either true sciatic nerve pain and referred low back pain. 80-90% of people’s symptoms will resolve. The speed of recovery can depend on the underlying cause of the symptoms. Generally if the pain is more muscular and referring into the leg, then the prognosis is generally faster than one which is caused by compression or irritation of the sciatic nerve. The nerve can undergo a rapid sensitisation process and is extremely sensitive to circulating inflammatory and immune chemical mediators which act on the nerve sheath, thus perpetuating the pain cycle (Genevay, Finckh et al. 2008). Stress, poor quality of sleep and being run down can also affect the experience of pain and the irritability of sensitised nerve. For those who don’t recover, pain and disability are not predicted by the size of the disc protrusion prolapse or degree of nerve compression, suggesting that other pain mechanisms are involved (Benson, Tavares et al. 2010, Barzouhi et al, 2013).
Is surgery an option?
Surgery should only be considered if there is progressive neurological weakness associated with the leg and/or other signs such as significant changes in bowel and bladder function (O’Sullivan, Lin 2014). Long term outcomes for surgery and conservative management have been demonstrated to have a similar outcome in terms of pain and disability (Benson, Tavares et al. 2010). Just because your pain is persisting does not mean that you need to go under the knife and other mechanisms of pain need to be addressed.
Although there can be many causes of sciatica, there is generally a good prognosis to this condition with some simple management strategies. Although this condition can be mechanical, a peripheral nerve can be sensitised by inflammatory chemicals surrounding the nerve. There is usually no need for scans or surgery unless there are associated neurological deficits.
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El Barzouhi A et al. (2013) Magnetic Resonance Imaging in Follow-up Assessment of Sciatica. New England Journal of Medicine 2013;368;11: 999-1007
Benson, R., S. Tavares, S. Robertson, R. Sharp and R. Marshall (2010). “Conservatively treated massive prolapsed discs: a 7-year follow-up.” Ann R Coll Surg Engl 92: 147–153.
Genevay, S., A. Finckh, M. Payer, F. Mezin, E. Tessitore, C. Gabay and P. Guerne (2008). “Elevated Levels of Tumor Necrosis Factor-Alpha in Periradicular Fat Tissue in Patients With Radiculopathy From Herniated Disc.” Spine 33 (19): 2041–2046.
O’Sullivan, P. and I. Lin (2014). “Acute low back pain: beyond drug therapy.” Pain management Today 1(1): 1-13.
Stewart J (2003) The piriformis syndrome is overdiagnosed. Muscle and Nerve – Issues and Opinions. 644-649.