Sciatica Pain Distribution
Where Does That Pain Come From?
|Sciatica is pain running down your leg in a pattern determined by the sciatic nerve. The pain often starts in the low back - (due to a herniated disc) - or in the buttock - (due to piriformis syndrome) - and extends as far as your toes. It can be accompanied by numbness, 'pins and needles' ("paresthesias") or, in more severe cases, actual weakness affecting the ankle or toes may accompany the sciatica.
Sciatica is a form of pain that is called a "radiculopathy" in medical terminology. This means that it often follows the path of a single spinal nerve root such as the Lumbar 5 (L5) or Sacral 1 (S1). This is often the case when sciatica is due to a herniated disc or bulging disc. If the cause is in the lumbar spine, the sciatica - or leg pain - is often accompanied by back pain.
Some patients also experience sciatica pain affecting all the dermatomes in the sciatic nerve, L4, L5 and S1. This sort of "pan-sciatic syndrome" may be due to piriformis muscle syndrome. This condition is due to a muscle in the buttock that goes into spasm and pinches the sciatic nerve.
When the sciatica symptom is due to a herniated disc, it often affects a single strip of skin or dermatome. A far lateral herniated disc affects the exiting nerve root in this picture, the L4 root is compressed by an L4/L5 lateral disk herniation. More commonly, however, the disk bulge is close to the body’s midline. The illustration shows an L5/S1 disk herniation affecting the transiting S1 root but leaving the L5 root undisturbed. The patient’s detailed distribution of symptoms must match exactly with the MRI findings in the spine before a back surgery can be recommended.
Sciatica Terms and Conditions:
Excerpt from the book on the subject of: Sciatica
The details of sciatica are a good example of the localization process. Sciatica refers to a pain in the leg which follows a particular pattern that is related to the course of the sciatic nerve: starting in the low back, running down behind the buttock and leg, then down the side of the leg and reaching around the ankle into the foot.
One of the most common causes of sciatica is a herniated lumbar disk at either the L4-L5 or L5-S1 level. These two herniations occur with about equal frequency. When the L4-L5 disk ruptures, it tends to rupture in a particular location on the posterior and lateral corner of the disk (toward the back and to the side), on either the right or the left. This disk extrusion doesn’t actually pinch the L4 nerve in the foramen or nerve canal at the L4-L5 level; instead, it usually pinches a nerve in the main spinal canal, the L5 nerve, that’s headed out through the foramen below at the L5-S1 level. That pinch almost invariably causes sciatica that runs all the way down the leg into the big toe. Similarly, an L5-S1 disk herniation usually pinches the S1 nerve and the resulting sciatica also runs down the leg, but it goes out to the little toe (See figure 7.1).
A pinch of the L4 nerve is far less common and is more complex to diagnose. It can be caused either by an L3-L4 disk herniation, which is relatively rare, or by an L4-L5 disk herniation that happens to point out laterally into the nerve canal. When the L4 nerve is pinched, the pain runs down the leg and may reach the ankle but not necessarily the toes. The other trick to an L4 nerve pinch is that the resulting pain can have a more prominent presence in the knee and on the anterior thigh. That’s because the L4 nerve doesn’t run into the leg entirely with the sciatic nerve; instead, part of it runs along the front surface of the thigh with the femoral nerve.
What about when both the big toe and the little toe are having sciatica pain? It could be that both your L4-L5 and your L5-S1 disk herniated at the same time; however, the chance of two disk failures happening exactly the same way and at the same time is very small. This symptom pattern tends to lead to the question of whether the whole sciatic nerve is being pinched somewhere along its course from the sacrum to the knee rather than one of the spinal nerves that leads into it.
One place where the entire sciatic nerve is pinched most commonly is in the pelvis, where the nerve exits from the inside to the outside of the pelvis through the sciatic notch and passes under a muscle called the piriformis muscle. Tension and spasm or increased muscle tone in the piriformis can cause a sciatica that affects the buttock and the leg, and reaches down to the level of the ankle but doesn’t go to any one of the toes in particular. A doctor can use physical exam maneuvers or tests to distinguish between the lumbar and pelvic forms of sciatica. The two also have some different features: piriformis sciatica tends to be worse with sitting but relieved by standing or walking, whereas the sciatica from lumbar disk herniation can often be relieved by sitting in certain positions (See figure 7.2).
Aside from sciatic nerve problems, entrapments of the tibial nerve at the ankle or tarsal tunnel syndrome, or entrapment of the peroneal nerve near the knee at the head of the fibula bone are common. Each of these will cause a specific pattern of pain numbness and weakness in the foot that can be mistaken for nerve root impingement by a spinal disk. If the physician considers these problems they may be sorted by physical exam, electrical nerve testing or by specialized imaging such as MR neurography (see Chapter 9).