What the Heck is Sciatic Anyway?

What the Heck is Sciatica Anyway?

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 outcome^1,2. 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 umbrellas of pathology.

1. 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.

Often pain is accompanied by what we term negative symptoms – numbness and weakness. During clinical assessment, tests of muscle strength, sensation over different areas of the skin, and reflexes (think doctor taping with weird hammer thingy over knee!) will often give clues to whether nerve compression is contributing to a patient’s symptoms.

2. 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.
3. 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 the numbness, weakness, tingling etc. 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.
4. 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.

As can be seen by these very brief descriptions, the type of condition can very often be identified by physical and verbal examination, frequently conducted by health professionals such as physiotherapists and osteopaths. Often patients are sent for imaging such as x-rays and MRIs. Unfortunately, these type of scans will often show structural changes (herniated/bulging discs etc.) that we know are actually very common in people without pain and often not associated with symptoms⁶. An MRI scan may show a nerve being compressed by a herniated disc, despite having no symptoms of nerve compression, and possibly lead a patient down the incorrect treatment path. Furthermore, seeing these “abnormalities” on film can very easily cause more harm than good, as patients and doctors will together start to focus on these findings and catastrophise the condition. Those patients with central sensitisation in particular will tend to respond poorly to this type of information.

This is not to say that imaging isn’t ever required. If a patient’s symptoms do not appear to respond to normal management, or if there are reasons to suspect something more serious (very occasionally thigh pain may be the result of a tumour etc.), imaging can be useful to rule out serious medical pathologies. If a patient does show signs of a compressive neuropathy in which the negative symptoms such as numbness and weakness show signs of worsening, then a scan may be useful to help identify the possible cause of this and potentially guide surgical options.

Because of these differences in the individual conditions, treatment needs to be tailored to the findings of the assessment. Nerve gliding techniques that may be beneficial for peripheral sensitisation could very easily flare up a compressive neuropathy, for example. Specific manual therapy to address an injured area of the spine in a case of referred pain may make things much worse for something with severe central sensitisation.

Because of this, it is important that patients suffering any of these symptoms have them accurately assessed and managed by someone experienced with these types of presentations, rather than simply following the advice of a friend or family member who may have suffered a seemingly similar, but medically very different condition.

References

1. 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).
2. 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).
3. Zusman, M. Mechanisms of peripheral neuropathic pain: implications for musculoskeletal physiotherapy. Phys. Ther. Rev. 13, 313–323 (2008).
4. 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).
5. 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).
6. 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).