In order to understand chronic back pain, it is important to understand Chronic Pain.
The back is a fairly complicated structure which is best understood when looking at it from a 3D perspective. Therefore, in order to explain the various sources of back pain, I will provide links to some excellent YouTube videos.
Herniated disc overview
Herniated disk annular tear
Herniated disk annular tears can heal
Studies show that most back pain is multifactorial. That is to say that it can be a combination of disc, facet and muscle. It can sometimes become be difficult to determine how much each structure is contributing to the pain. This becomes all the more difficult when pain becomes chronic as the pain tends to spread over the lower back rather than localizing to individual structures. In general, when pain is predominantly limited to the back, it is likely originating from the facet joints. The disc is also very well innervated and even if it bulges without rupturing, it can cause midline back pain.
If the pain is radiating down the leg, it is usually coming from compression of the sciatic nerve. The nerve can generally be compressed at 3 levels. In younger people it is usually a herniated disk that has spilled its contents causing pressure and inflammation of the nerve. In older patients, the disc is more dried out but the facet joints have become more osteoarthritic. This causes the facet joints to enlarge and they can eventually encroach on the canal where the nerve exits the spine. Over time, with diffuse arthritis, this can lead to spinal stenosis. This causes multiple parts of the spinal cord to be compressed. We often see this in elderly patients with bilateral leg pain. Sometimes the sciatic nerve can be compressed at the level of the pyriformis muscle.
Some patients are tender over their SI joint which may be contributing to their pain. Many of my chronic pain patients have spasm of their back muscles. This is can often be felt if not seen. Sometimes, there are palpable trigger points.
Through a combination of imaging, history and physical examination when can generally tease out the contributors to back pain. Sometimes we do specialized tests such as epidurals and facet injections which may serve to identify the cause of the pain as well as treat it.
Contrary to popular belief, the MRI is not a great tool for teasing out the causes of back pain. In most people over the age of 50, there are always abnormalities on the MRI regardless of whether the patient has pain or not. Often there are multiple abnormalities involving multiple discs and facet joints. The MRI may read ‘Multi-level degenerative disc disease and facet joint arthropathy’ which really does not point out the main pain generator. Patients are often insistent on getting an MRI while most physicians know that the MRI will hardly contribute to what they already know. Many studies have shown that the overwhelming majority of back MRI’s do not change management. MRI’s are most useful if we are planning procedures or surgery or if we want to rule out less common causes of back pain.