Low back pain and lower extremity pain must be distinguished. Although the two are often lumped into one category, to a neurosurgeon, they represent different pathologies. Lower extremity pain is often what is called a “radicular pain.” This refers to a pain which shoots down the leg, from the low back or buttock. It usually results from the pinching of a nerve, and appears to radiate down the leg in the distribution of the nerve. When the “pinching” of the nerve is mild, one may experience a numbness. When it becomes more severe, pain may develop. And, if it is quite severe, nerve damage will result, and weakness may also ensue.
Each nerve in the lumbar spine has a characteristic sensory distribution, motor function, and reflex. What this means is that a nerve will supply sensation to a certain part of the leg. For example, the S1 root, which is the first sacral root, supplies sensation to the lateral aspect of the foot (little toe). Each nerve also supplies a characteristic muscle. The S1 root supplies the gastrocnemius, which allows each of us to stand on our toes. And lastly, several of the nerves in the lumbar spine have a reflex associated with them. The S1 root has the Achilles reflex, which is elicited by tapping on the the heel tendon. A clinician will put together the symptoms, with an exam, and with sophisticated testing, to arrive at a diagnosis.
Neurogenic claudication refers to pain in the lower extremities brought upon by walking. This is often caused by pressure upon the spinal nerves within the spinal canal, usually the result of the ligamentum flavum bulging into the nerves when standing. This type of pain must be distinguished from lower extremity pain called vascular claudication, which is due to insufficient blood supply to the legs (arterial insufficiency), and it brought upon by walking. The difference between the two is that merely standing (without walking) causes neurogenic claudication but not vascular claudication.
Low back pain, on the other hand, is not due to the pressure on a nerve root, as lower extremity pain is, but is more of mechanical pain, due to strain and sprain of the ligaments and tendons of the low back, and due to degeneration of the disk space and facet joints which hold the spine together.
Other ailments can cause low back pain, such as referred symptoms from other organ (bladder, gall bladder.)
It is extremely important to match the symptoms a patient experiences, with the symptoms one would expect based on the physical exam, and other tests. If all match, then treatment can be focused at the root of the problem, and successes will be greater.