The sciatic nerve is formed in the lower spine by the union of L4 to S31 nerve roots and exits the pelvis through the greater sciatic foramen, below the piriformis muscle (deep in the buttock). The nerve then runs along the back of the thigh, into the leg, and ends in the foot. Sciatica occurs when this nerve is inflamed, irritated, and/or mechanically compressed at its nerve root end.
There May be a Genetic Cause for Sciatica
Sciatica caused by degenerated and/or herniated discs in the lower spine may have a genetic origin. Research suggests2,3 that certain genetic factors are more prevalent in specific populations. These genetic defects may cause the contents of a disc to become weak and susceptible to external stress. Over time, the proteins in the disc may breakdown, compromising the integrity and function of the disc.
Herniated or degenerated discs may irritate or compress the nerve roots in the lower spine, causing sciatica.
Sciatica Is Caused by a Problem in the Lower Back
Sciatica occurs when one or more sciatic nerve roots in the lower back is irritated or compressed as it exits the spine. Each nerve root is responsible for sensory and/or motor control of a specific part of the thigh, leg, and/or foot and toes. Depending on the nerve root affected, pain and other symptoms may occur along the distribution of the nerve.
Piriformis Syndrome Feels Like Sciatica, but It isn’t the Same
Piriformis syndrome is a condition where the piriformis muscle swells and/or develops spasms due to overuse or inflammation and irritates the sciatic nerve (which lies right below it). The nerve may also get entrapped in the muscle. Piriformis syndrome causes sciatica-like pain, tingling, and numbness that often starts from the lower back and runs down the leg and into the foot.4
While the pain and discomfort from piriformis syndrome may feel similar to sciatica, it is not caused by a compressed sciatic nerve root in the spine. Piriformis syndrome pain occurs due to compression of a part of the sciatic nerve near the piriformis muscle. The pain usually follows the same pattern in the leg as a compressed sciatic nerve root.
See Symptoms and Diagnosis of Piriformis Syndrome
Pain from Arthritis or Joint Problems Is not True Sciatica
Arthritis or other inflammatory conditions around the hip joint may cause pain to travel down the leg similar to sciatica. This pain is usually referred down from the pain source and is not radicular nerve pain that originates from the nerve roots.
Other conditions, such as sacroiliac joint dysfunction or sacroiliitis can cause sciatica-like pain that extends down the back of the thigh but usually ends before the knee. This pain can be acute and debilitating, as in sciatica, and is caused by an abnormal motion or malalignment of the sacroiliac joint in the pelvis.5
While rare, tumors, infections, or severe nerve damage in the lower spine can cause sciatica symptoms and require immediate medical attention.
See When Sciatica Pain Is a Medical Emergency
In order to obtain effective pain relief from lower back and leg pain, it is important to correctly identify the exact underlying cause of sciatica. A doctor can conduct specific diagnostic and clinical tests to identify the cause and rule out serious medical conditions. Treatments for sciatica and other lower back conditions are usually different. Obtaining an accurate diagnosis can help formulate an effective treatment plan to target the specific cause.
See Diagnosing the Cause of Sciatica
References
- 1.Giuffre BA, Jeanmonod R. Anatomy, Sciatic Nerve. [Updated 2018 Dec 16]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2019 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK482431/.
- 2.Feng Y, Egan B, Wang J. Genetic Factors in Intervertebral Disc Degeneration. Genes Dis. 2016;3(3):178–185. doi:10.1016/j.gendis.2016.04.005
- 3.Hanaei S, Abdollahzade S, Khoshnevisan A, Kepler CK, Rezaei N. Genetic aspects of intervertebral disc degeneration. Reviews in the Neurosciences. 2015;26(5). doi:10.1515/revneuro-2014-0077
- 4.Hicks BL, Varacallo M. Piriformis Syndrome. [Updated 2018 Nov 15]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2019 Jan-.Available from: https://www.ncbi.nlm.nih.gov/books/NBK448172/.
- 5.Raj MA, Varacallo M. Sacroiliac (SI) Joint Pain. [Updated 2019 May 12]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2019 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK470299/.
