Common Causes of Back Pain

Mechanical origin back pain. If your lower back pain is caused by mechanical origin and not sourced by an internal organ issue, an infection, or a tumor, then you can make some reasonable assumptions. For instance, the most common structure that causes pain in the back is the inter-vertebral disc. The disc is made up of two tissues:The nucleus pulposis, and the fibrous disc. Think of a disc like a jelly doughnut. The nucleus would be the jelly, and the doughnut the fibrous disc.The reason the disc causes pain is that over time, the nucleus migrates to the outer layers of the disc, causing a bulge. The outer fibers have pain sensitive nerve endings, and often, lower back pain is caused by the disc bulging. Pain of discal origins is reoccurring because the disc bulge can come and go. Usually, in this state, the pain is felt just in the back. Depending on the actual direction of the bulge -- central, or lateral -- the pain can be more on one side than the other, or in the middle and on both sides.

As the bulge progresses, eventually the outer fibers of the disc can herniate with a large but contained bulge occupying space outside the disc boundaries (HNP). The reason this is an issue is that the neighborhood that the disc lives in is filled with pain sensitive tissues -- specifically the nerve roots of the spinal cord -- called the Cauda Equina in the lower part of the spinal cord, and the nerve roots as they exit the spine through the foramen. A herniation can actually irritate or even compress a nerve root. This sort of mechanical defect gives rise to pain that is in the periphery -- usually the butt, the thigh and the lower leg. Depending on the severity of the compression or irritation, the pain might be felt in the foot as well.The location of the symptoms is helpful in that specific nerves refer to specific locations, also known as dermatomes. While a back pain exercise approach might be helpful in treating a HNP, often selective injections, usually provided by a physiatrist or an anesthesiologist, where a steroid and an anesthetic are introduced into the spinal canal around the HNP, will be definitive in diagnosing the problem. Often selective injections, while diagnostic, are also curative. Unfortunately, HNP is often a recurring issue, and pain is thought to reoccur with each episode being more severe, and lasting longer, which makes sense if you think of the HNP as worsening over time. This continues as an issue until about age 55 or 60 when the nucleus dehydrates enough to make the herniation less likely to occur.

Occasionally, the disc will rupture, and the nucleus will escape the boundaries of the disc causing severe LBP usually with nerve root compression. The reason this occurs is that the nucleus, which is hydrophilic, binds water with astonishing affinity. It has been said that the nucleus will weigh 1000 times more wet than dry. So as the nucleus escapes the boundaries of the disc, one can imagine it expanding as it binds water increasing its weight by almost 1000 times. The nerve root compression that follows is short lived though, because the nucleus loses its ability to bond water fairly quickly. The tissue has a short half life, between one-and-a-half and seven days, which means that over time the nucleus actually shrinks and the pressure on the nerve root subsides. Clinically, this translates into about 6 weeks.During this time, we usually see the pain migrating from distal to central locations and we see less evidence of nerve root compression -- specifically loss of muscle function and loss of sensation, and we see more evidence of nerve root irritation, usually pain, some tingling and possibly areas of numbness.

In the event that the fibrous disc is ruptured in such a manner that it is the disc itself and not the nucleus that is pressing on the nerve, then surgery is frequently required to remove the part of the disc that is pressing on the nerve root. Time will not allow the fibrous disc to dissolve in the manner that the nucleus does.

Facet Joint Lower Back Pain. The facet joint is another source of lower back pain. While disc bulges tend to feel worse with sitting, pain of facet joint origin tends to be worse with standing. The facet joints are typical synovial joints that have cartilage surfaces, a joint capsule, and ligaments associated with them. Facet joints are usually irritated by impact loading but wear and tear -- or aging -- can also play a roll. Posture, fitness and routine activities are all actors in pain that originates in the facet joints and the surrounding structures. In younger, active people, the facet joints play a major role in facet joint pain, as does trauma. It is not uncommon to see pain in the lower back in people who have been involved in a motor vehicle accident that is caused by traumatically induced ligament and capsule sprains.

Trauma Induced Lower Back Pain. There are two important ligaments that impact lower back pain syndromes. The first lives on the tips of the spinous processes and travels the length of the spine (called the supraspinous ligament), and the other lives between the spinous processes, (called the interspinous ligament). These two structures are often involved in LBP syndromes that originate with trauma.

It is possible, but unusual to "strain a muscle" in the lower back. I say this because the anatomy is more or less protective against overstretching muscle in that region, especially with movements into rotation. That is not to say that there is no muscle involvement LBP; instead, muscle guarding is typically more of a symptom of LBP rather than the cause. In back pain therapy, we go a long way toward dealing with the muscle guarding associated with LBP, but resolving the muscle guarding does not do much for the underlying pathology. That must be addressed separately in order to successfully treat LBP.

There are other reasons for LBP, such as sacro-iliac joint dysfunction. The pelvis, if subluxed with one wing of the pelvis slightly out of position, causes a change in the posture of the sacrum, and this in turn changes the posture of the lower lumbar spine. The SI Joint dysfunction must be addressed in these situations in order to resolve this cause of mechanical LBP.