What the Heck is Sciatica Anyway?
By Sam Gilbert.
Almost everyone reading this will have experienced or know someone who has experienced the strange phenomenon commonly referred to as “sciatica”, where pain magically travels from the back, down through the sciatic nerve, into the leg, calf and sometimes even the foot. These symptoms can affect different people to differing degrees, with some people complaining of a dull, annoying ache in the thigh that comes on after repetition of a certain activity, whereas others may experience intense shooting pain down into the foot, along with other sensations such as numbness, weakness and tingling.
While “sciatica” is still a frequently used lay term to describe these symptoms, it is no longer widely used by the medical profession. Symptoms in the thigh originating closer to the spine, whilst similar in nature, can signify a number of different conditions. While these different conditions can coexist, there is usually one prominent driver and research suggests that providing a targeted treatment to the specific condition increases the likelihood of a better outcome1,2. This is why a thorough assessment of the individual is critical in the management process.
In the spectrum of conditions that can refer symptoms into the back of the leg, we generally have 4 main umbrella’s of pathology.
- The first is what we refer to as a compressive neuropathy. This is where the nerve is exposed to some direct compression as it exits the spine. Whilst compression on a nerve can frequently occur in many asymptomatic individuals3, for a number of complex reasons, sometimes the compression is sufficient to cause a degree of dysfunction in the nerve. These conditions are often worse with positions of extension, i.e. walking and standing4.
- The second umbrella of pathology is what we term peripheral sensitisation. This is where the nerve essentially becomes irritated or inflamed, often due to injury or sensitivity to a nearby structure, in the spine, for example, or a muscle through which the sciatic nerve travels. These type of issues are sometimes accompanied by what we term positive symptoms – tingling/pins & needles, and increased sensitivity to touch. On assessment, pain is often provoked by movements designed to stretch the nerve5.
- The most common cause of pain in the thigh originating from the back is what we term referred pain. This is essentially when the brain reads stress on a structure in the back as coming from another part of the body (e.g. the leg), and in doing so creates a painful experience in this area. Symptoms in these type of conditions are not typically associated with other neural symptoms such as numbness, weakness, tingling etc. as described in the other conditions above. Movements that stress the sensitised area of the back may also reproduce the pain in the leg, as may direct palpation (touch) over the referring area of the spine.
- The forth category is driven by what we term central sensitisation. Whenever we experience pain it is essentially a protective reaction from the nervous system in response to some type of threat or perceived threat. The reaction can be modified by a number of different factors, and because of this there is rarely a direct correlation between the amount of structural damage and the amount of pain experienced. The central nervous system (the brain and spinal cord) have the ability to greatly up-regulate the amount of pain experienced, and in some cases an individual may experience pain even in the absence of any structural damage. Assessment of this type of condition requires a thorough verbal consultation and often includes questionnaires to ascertain the degree of psychological influence on the pain.
- Schäfer, A., Hall, T. & Briffa, K. Classification of low back-related leg pain—a proposed patho-mechanism-based approach. Man. Ther. 14, 222–230 (2009).
- Schäfer, A., Hall, T. M., Lüdtke, K., Mallwitz, J. & Briffa, N. K. Interrater reliability of a new classification system for patients with neural low back-related leg pain. J. Man. Manip. Ther. 17, 109–117 (2009).
- Zusman, M. Mechanisms of peripheral neuropathic pain: implications for musculoskeletal physiotherapy. Phys. Ther. Rev. 13, 313–323 (2008).
- Morishita, Y. et al. Measurement of the local pressure of the intervertebral foramen and the electrophysiologic values of the spinal nerve roots in the vertebral foramen. Spine 31, 3076–3080 (2006).
- Dilley, A. & Bove, G. M. Disruption of axoplasmic transport induces mechanical sensitivity in intact rat C-fibre nociceptor axons. J. Physiol. 586, 593–604 (2008).
- Baker, A. D. Abnormal magnetic-resonance scans of the lumbar spine in asymptomatic subjects. A prospective investigation. in Classic papers in orthopaedics 245–247 (Springer, 2014).
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