Low back pain

Low back pain is very common, 50% of Americans will have some in their lifetimes. It is one of the more common reasons patients seek my care or that of other Osteopaths. Although there are a number of causes of low back pain, most is considered by conventional medicine to be nonspecific or “Mechanical” low back pain. I like to call this “Garden Variety” low back pain. In Osteopathic Medicine we consider the cause most often to be Somatic dysfunction, which I explain on my Website “About Osteopathic Manipulation”. This type of pain is the most likely to benefit from Osteopathic manipulation. Pain associated with other cases sometimes can be helped as well, but less predictably. Somatic dysfunction is where the muscles are made to contract by a hyperactive reflex arc between the muscle stretch receptor and the spinal cord, which then sends a signal to the muscle to contract. A constantly contracting muscle becomes painful, and sometimes if intense enough would be a “spasm”.  Exactly why the pain can be so intense, and why it can come on suddenly isn’t completely clear, but is typical. We all have some Somatic dysfunction, even without pain, but if it becomes more severe it goes above a threshold which then causes pain. This reflex may be “tweaked” by a minor motion, sometimes resulting in severe pain from seemingly minor motion. There was a more significant injury earlier which set up the pattern, which may or may not have resulted in pain at the time, but a quick, minor move may be enough to bring it over the threshold even years later. It is very common to have self-limited episodes of back pain, where the back seems as if it “goes out” suddenly, and often will resolve without any specific treatment. Some people live all of the time above the threshold, with chronic daily pain. The goal of manipulation is to quiet down he reflex circuit to well enough below the threshold to have a buffer against future episodes. 

 

There are other causes of back pain, although more often there may be coincidental anatomic changes which are not actually causing pain, but are attributed as the case often by non-osteopathic practitioners. 

 

There are very serious and potentially life-threatening causes of back pain, but thankfully these are quite uncommon compared to the myofascial pain of Somatic dysfunction or other benign causes. Generally cancer, infection and fracture are the serious cases to consider. I adults most “bone cancer” has spread from other cancers, although the patient may not have yet been diagnosed. Generally this pain is gradual in onset, as opposed to the “going out” scenario, and isn’t very specifically related to movement as is garden variety pain, where it may be painful to bend over but not arch back, twist one way but not the other, etc. There are often other symptoms of fatigue, unexpected weight loss. Infection in the back is another serious and urgent cause of back pain, but is rare outside of injection drug users who have bacterial spread in the blood. Compression fractures are usually in older adults associated with osteoporosis, and are sudden in onset, generally due to a minor fall or other injury.

 

There can be other benign causes of pain with a specific anatomic point source pain generator, although as I say many people may have “abnormalities” on X-ray or MRI and have no pain, so in patients with pain this may or may not be the cause. “Arthritis” of the spine or disc related problems may be specific sources of pain. It can be difficult to know based on clinical symptoms, examination findings or even imaging studies. I had sudden onset of low back pain 35 years ago building a deck, and visualizing the location in my mind’s eye, and knowing the anatomy, I would have placed it right at the L5-S1 disc, the lowest. But it was not coming from the disc because I could resolve the pain by curling myself up like a pretzel, utilizing the Strain-Counterstain Osteopathic technique on myself. The pain was primarily muscular, and since the muscles operated across L5-S1, the brain’s simplistic representation was “L5-S1”.    

 

Spinal disc herniations are generally not a cause of pain, although they can cause limb pain by compressing nearby nerves. When I was in Osteopathic Medical School, the teaching was that there was no pain because anatomists couldn’t find any pain receptors in the disc. Much later it was felt that there could be “discogenic” pain. This would be defined by an interventional procedure called a “provocative discogram”, in which a needle would be placed into the disc, and if while injecting contrast dye under pressure, the dye leaks from the disc and the patient’s pain goes up with the pressure, that defines discogenic pain. This approach has largely fallen out of favor in the Pain field, in part because nearby discs can be injected also causing pain, and basically the only treatment available would be disc replacement or spinal fusion surgery. There are a lot of terms used in describing disc disease. The intervertebral disc is made up of the central, jelly-like “nucleus pulposus” and is held in place around the margins of the vertebra by a tough fibrous tissue called the “annulus fibrosus"   There is “degenerative disc disease”, largely age-related changes, where the disc loses water content, shrinks down and narrows the disc space between the 2 adjacent vertebra. There can be disc “bulges” where the edge of the disc, the annulus, goes beyond where it normally should be, but not beyond the edge of the vertebra. Generally this doesn't cause a problem compressing the nerve unless there are other contributors to narrowing the space around the nerve, such as bone spurs from disc degeneration or arthritis of the little facet joints, discussed below. Beyond bulges are “protrusions”, where the disc goes out beyond the edge of the vertebra. Although somewhat more likely to cause problems, in one study of MRI in patients who have never had back or sciatic type pain, 40% have disc bulges and 10% have disc protrusions. One man even had a disc “extrusion” where a piece of the inner nucleus was squeezed out and floating free in the spinal column, but was not pushing on a nerve so didn’t cause pain. A disc “herniation” can result in a bulge, protrusion or extrusion. This is where there is a tear in the fibers of the annulus, and some of the nucleus pushes out. There terms can be very confusing to patients, especially when they may not have anything to do with the cause of the pain and could lead to unnecessary interventions including surgery. 

 

Disc herniations can and do cause pain if they compress the nerves as they exit the spinal column. Although the problem is in the spine, it is a characteristic of nerve compression pain that it feels as if it is coming from along the nerve. It is like the phantom pain of the amputee, were the missing part of the leg is where the pain feels like it is. “Sciatica” is a term often used for nerve compression pain emanating from the low back, although in my experience patients complaining of sciatica often do not have this pattern. Classic sciatica begins in the buttock, generally not in the midline of the back itself, and seems to travel down the back of the thigh, calf and then wraps around the inner ankle bone into the foot. The 4th and 5th toes my have burning or tingling. Because the lowest level of the low back, L5-S1 where the lowest vertebral bone rests on the sacrum, a bone formed of a number of fused vertebra which form a triangular bone which sits between the two iliac bones “hip bones”. This level is the most common to cause nerve pain, and so most nerve compression pain is classic sciatica, but if higher up nerves are compressed, the location of the pain changes, in a pattern which can be helpful diagnostically. 

 

In the development of the fetus, we start out as a long tube made up of vitally similar segments. Some segments merge and become very specialized, as in or brain and head, some into the arms or legs. The spine retains the segmental pattern, so a “segment” is made up of the vertebral bone, the disc, and a pair, right and left, of spinal nerve “roots”. A compressed or pinched nerve, if it causes pain we call that “radicular” since the latin word for root is “radicle”. Things getlittle more complicated in the low back because the spinal cord, from which all the nerves peel off at their segment, is shorter than the bony spinal column. The end of the cord is about L1 or L2 more near the top of the low back. So the nerves need to travel past a couple of disc levels before exiting at the level associated with the nerve. Commonly the nerve is compressed in the canal,called the foramen, as it exits the spine. A foramen is just a hole or tunnel. This may be narrowed in several ways. A common way, especially in younger persons who aren’t likely to have the other problems, is a protruding disc. The edge of the disc runs all along the edge of the adjacent vertebral bones, but herniations in some locations aren’t really a problem. Since the spinal canal is behind the main vertebral body, enclosed in the parts of the protective arch, herniations in the front bulge into the fat and muscle in the front, and aren’t big enough to cause a problem. If the bulge is to the rear, and especially if off to one side or the other, it can compress the nerve as it is in or just outside of the canal. Typically this will be one or the other side and not both at the same time, because if both sides are bulging then so is the center, and that tends to cause other problems, spinal stenosis or the cauda equina syndrome by compressing the bundle of nerves coming from the end of the spinal cord. The spinal cord and the nerve roots don’t like to be touched. They float in the thin fluid enclosed inside the spinal canal, called cerebrospinal fluid. There is normally plenty of fluid around the nerve root until it is outside if bony column when the “dura mater” the thick membrane surrounding the brain and spinal cord merges with the nerve now nestled in muscle and fat. The foramen that the root passes is dynamic in its size and capacity, because the bony part of the canal is formed by a notch in the arch of the upper and of the lower vertebra. When we move, these bones come closer together and father apart. When they come closer, and if other problems are contributing to the narrowing, there might be pain only in certain positions. Typically if compressed in the foramen, backward bending of the spine will worsen the compression so positions in which this happens, including standing or walking, tend to aggravate. In addition to the disc, the canal may be encroached upon by bone spurs, which occur as a result of disc degeneration, coming from the edges of the vertebral body. If these protrude backwards and outward they can narrow the foramen. There is a bony arch coming from each vertebral body, to protect the spinal cord and nerves. To allow smooth movement and to coordinate the arches at adjacent levels, there are little joints on each side from one arch to the next. This are cartilage joints and can develop osteoarthritis like the knuckles and the knees. Bone spurs, technical term “osteophytes” also occur as a result of Osteoarthritis, and if they go backward and inward can narrow the foramen. Sometimes other things can contribute to the narrowing (technical term stenosis) including thickened ligaments and sometimes a forward or backward slippage of on vertebra on the other known as a “listhesis”. The nerve root can also be compressed at a level or sometimes 2 levels above where it exits. As it nears it’s exit point it lies farther to the side, and can be compressed in the “lateral recess”. So a single nerve root, which may have a characteristic pattern of pain, might be compressed at one of 2 or even 3 levels. Stenosis or narrowing in the foramen, the lateral recess or the main canal can be of varying severity. Usually symptoms aren’t associated with narrowing less than “severe” or “moderately severe” on MRI reports (the nerves can’t be seen on X-ray), and these narrowing are also common in patients with no back or limb pain. Stenosis of the main canal can cause a pain pattern of “neurogenic claudication” Claudication can occur with narrowed arteries limiting blood flow into the buttocks or legs, but neurogenic claudication causes a somewhat similar pattern, in which the pain comes on the longer and more vigorous a person walks, and to relieve the pain they can’t just stop but must sit or bend forward. So disc problems are common, may or may not cause pain but if they do it is radiating limb pain one not typically back pain.

 

Back pain, midline or at least symmetrical (although can be right or left) canbe caused by pain arthritis of the little facet joints, although many many of us as we age develop this arthritis and do not have pain. Some features can be helpful. The pain is usually pretty close to the midline of the spine, at the level of the painful joint, although may travel down and out some, sometimes at L5-S1 down the back of the thighs, but not beyond the knee like radiculopathy. Because the axis of bending of the spine is through the middle of the vertebral body, bending forward opens up or gaps the facets, and generally is more comfortable, and bending backwards puts more pressure on the joints and is painful. This can be useful diagnostically, although myofascial pain can have the same pattern depending on the nature of the original injury. 

 

Since painless arthritis is common, finding changes of facet arthritis on X-ray or MRI does not at all prove that the joint is the source of pain. If suspicious based on features noted above, and if disabling, diagnosis can be determined or refuted by specialized injections which are done under fluoroscopy or video X-ray. There are 2 approaches, one is to inject a local anesthetic directly into the joint. If the pain is received for the duration of the anesthetic, from 2-18 hours depending on which anesthetic was used, that is considered diagnostic of acetogenic pain. Usually a cortisone type steroid is injected as well. This can be helpful for a few months, although it has been hard to prove there is general benefit in randomized trials comparing to a sham injection. A more useful therapeutic approach is to block the small nerve that goes to the joint, called the median branch, which sends signals of pain to the spinal cord and brain. This nerve can be “ablated” or “burned” by a catheter which emanates radiofrequency waves, and heats up the tissue. This blocks the pain transmission. This can also cause a small area of numbness of the skin in the area, and weakness a small area of muscle, but usually these are not significant. The nerve does regrow, and pain may reoccur in 3-18 months, although the procedure can be repeated. To see if the procedure might be effective, diagnostic injections with local anesthetic are done to see if the pain is temporarily resolved. These diagnostic injections are called “median branch blocks”, and the radiofrequency procedure is called RFA, radiofrequency ablation, median branch radiofrequency rhizotomy and other names, most commonly “RFA”. 

 

Non-interventional approaches to back pain include physical therapy. One approach, developed at New England Baptist Hospital, is called “Functional restoration” or often “Back boot camp”. This involves vigorous exercise aimed at strengthening the back muscles, recognizing that there will be pain involved in doing the exercises for a few months, but physical therapists are trained to coach people through this. I have generally recommended strengthening exercises in between episodes of pain, or after the pain has been reduced or resolved with my approach to manipulation.