Back Pain

A vertebra consists of a body which is in front and the laminae (1 on each side) at the back. The right and left laminae join each other in a V like the roof of a house. The apex of the V is prolonged to form the spinous process (the bumps you can feel when you run your hand along the mid line of your back). The joined laminae are sometimes called the neural arch (Fig. 1). The laminae enclose the spinal canal which contains the spinal cord and nerve roots. Vertebrae are joined to each other by the intervertebral disc in front and by facet joints (right and left superior [upper] and right and left inferior [lower]) at the back. The intervertebral disc consists of an inner part, the nucleus pulposus (the pulpy core) and an outer part the annulus fibrosis (the fibrous ring). The nucleus is gelatinous and the annulus is tough and sinewy (Fig. 2). The superior and inferior facets are connected by the pars interarticularis (the part between the facet joints). The spinal cord ends opposite the first or second lumbar vertebra (L1 -2) and the lumbar and sacral nerve roots leave the spinal cord and travel downwards through the spinal canal until they exit from the spinal column at their respective levels (Fig. 3). The spinal cord and nerve roots are bathed in cerebrospinal fluid (CSF) and covered by an inner thin membrane (the arachnoid mater) and an outer thick membrane (the dura mater). Between each pair of vertebrae 2 spinal nerves, one on each side, emerge through an opening (intervertebral foramen) formed by the overlap of the upper facet of the vertebra below, and the lower facet of the vertebra above.

Vertebrae are also connected to each other by a complex of ligaments. (Figs. 4, 5)

A number of muscles are attached to the vertebral column. The most important is the sacrospinalis (erector spinae) which is the name of a group of muscles that originate from the pelvis and are attached to the vertebrae from behind. It brings the back to the vertical from the bent position as well as controlling side to side motion.

Where does back pain come from? Tiny pain sensitive nerve endings are located in the ligaments that join the vertebrae together, in the muscles alongside the spinal column, in the facet joints, on the annulus portion of each intervertebral disc, in the periosteum covering certain bone surfaces and on the dural membrane that covers the nerve roots. Pain from irritation of these nerve endings is usually felt by the patients in or across the low back region and may sometimes spread to the buttocks and groins. Occasionally the pain travels down the back of the thigh(s) towards the knee but never below the knee. This is sometimes called "referred pain". Pain from the facet joints is usually aggravated by arching (extending) the back but not by bending forward (flexing).

In common back strain, it is these ligaments and muscles that are stretched and become painful. It is not possible to determine precisely which ligament or muscle is affected. Most heal in a few days or at most a few weeks and are not likely to be a source of continuing pain.

Another type of pain is that caused by irritation or compression of a spinal nerve root. Such pain usually travels all the way down the extremity to the shin, calf, ankle or foot. It is often, but not always, accompanied by neurological findings such as numbness in a specific area of skin supplied by that nerve root, weakness of specific muscles supplied by that nerve root, decreased or absent knee or ankle reflex (depending on which nerve is affected) and limited nerve stretch test (straight leg raising or hip extension with the knee flexed). This nerve root or radicular pain is different from and must be distinguished from the local or "referred" pain from back muscles, ligaments and facet joints.

Any discussion of back pain is often dominated by the term "Degenerative Disc Disease". This is an inappropriate phrase because what is being described is usually not a disease but normal aging change. A better description would be "age related" change. This normal process produces typical x-ray and CT or MR changes which are commonly misinterpreted by physicians as being evidence of something abnormal. In turn this may lead to unnecessary investigation and, sometimes, surgery.

With gradual aging, there is loss of water from the nucleus pulposus with resulting thinning of the disc space between the adjacent vertebrae and this can be seen on plain x- rays. The narrowing of the disc space causes the annulus fibrosis to "bulge" and this can be seen on CT or MR scans. It does not usually cause symptoms but if the bulging is excessive one or more nerve roots may be compressed with resultant symptoms. The bulge is centrally located and as there is usually plenty of room in the spinal canal, nerve roots are rarely compressed. A lateral bulge, if very large, may sometimes compress a nerve root. This process of bulging is not the result of trauma. Aging is often associated with the formation of a bony out growth (spur, osteophyte, exostosis) at the periphery of the vertebral body. Another result of the height loss is that the facet joints are distorted. This can cause wear and tear changes in them (described as "facet arthritis"). Sometimes the disc narrowing is accompanied by backward ("retrospondylolisthesis") (Fig. 6) or forward (degenerative or pseudo spondylolisthesis) displacement of the upper vertebra on the lower. These tongue twisters simply mean slipping of a vertebra (spondylos=vertebra, listhesis=slip, retro=backwards). (True as opposed to pseudo spondylolisthesis is the result of a bony defect in the structure of the vertebra and will be discussed later {Figs. 7, 8}). The incidence of these aging changes is affected by heredity and race. Some families are predisposed to develop marked changes at an early age. Aging change is commoner in Caucasians than in Negroes and Orientals. There is no convincing evidence that these changes which are so obvious on the x- ray or scans cause pain. In most people who have back pain in the presence of aging change, the pain is the result of ligament or muscle strain and not because of the age change seen in the x- ray.

There are three conditions in which aging may cause symptoms: 1) a disc problem (herniated, sequestrated, ruptured disc); 2) spinal stenosis (narrowing of the spinal canal); and 3) facet arthritis.

Sometimes some fibers of the annulus fibrosis may give way or tear, either spontaneously or from an injury, resulting in back pain. This usually heals in a few weeks with resolution of the pain. However a tear may allow some of the nucleus pulposus to protrude into or even completely through the annulus (called "herniation" or "sequestration"). This may or may not irritate or compress one or more nerve roots (Figs. 9, 10). Even so, the great majority of patients with such a protrusion or rupture get better in a few weeks with healing of the tissues and resolution of the pain. A few such patients fail to get better and may require surgery. A few others may get better but are vulnerable to recurrent pain in the future.

In spinal stenosis (Fig. 11), the gradual formation of bony outgrowths narrows the spinal canal and the openings through which the spinal nerves emerge. This condition is not caused by trauma. In people who have a small diameter spinal canal to begin with, the nerve roots are more vulnerable to compression. This narrowing of the spinal canal produces numbness and weakness ("my legs feel rubbery") in the legs, typically brought on by walking and disappearing slowly with rest. If the symptoms are severe and disabling, surgery to decompress the affected nerve roots may be required.

The above pre-existing conditions can become symptomatic following trauma. In the case of a herniated disc, presumably the nucleus pulposus had worked its way partially through the annulus fibrosis but not far enough to produce symptoms. Then an injury, sometimes relatively trivial, permits the nucleus to escape completely. In the case of spinal stenosis, the canal is already narrowed but not sufficiently to cause symptoms. Then if an injury causes a disc to bulge or herniate, further narrowing the spinal canal, symptoms are produced. Facet arthritis is the result of loss of disc height distorting the facet joints. It can be the cause of chronic intermittent back ache. When seen soon after an injury it is a pre-existing condition as it takes years for the x- ray changes of facet arthritis to occur. Whether or not it is aggravated by trauma is a moot question. For this to be true, the injury would probably have to be severe rather than a simple lifting strain.

In spondylolysis (Fig. 8) the pars interarticularis instead of being made of bone is made of gristle. As the gristle is not calcified, it appears as a defect in the x- ray. This is spondylolysis. While the gristle is very strong it is not as strong as bone. Over time it may stretch permitting the upper vertebra to slip forward on the lower one. This is spondylolisthesis. Both spondylolysis and spondylolisthesis occur most commonly in the 4th and 5th lumbar vertebrae.

The exact cause of spondylolytic spondylolisthesis is unknown. It occurs in 5% of Caucasians and in almost 20% of Inuit. There is no clear evidence that it is caused by trauma. It is commoner in ballet dancers and acrobats who arch their backs a lot. The majority of people with it have no symptoms. But symptoms (back ache) can occur in a person with pre-existing and painless spondylolisthesis as the result of a strain or repetitive lifting. Once symptoms commence, they tend to recur.

In this congenital condition, the lowest (5th) lumbar vertebra is fused to the sacrum, reducing the number of joints in the lumbar spine from 5 to 4. It does not cause symptoms. There may be more than usual wear and tear of the next disc up (between L4 and L5) causing premature aging change in some patients. Often the transverse process of the 5th lumbar vertebra is connected to the pelvis by means of a false joint (pseudoarthrosis) but this does not cause pain.

In this congenital condition the first sacral segment is separated from the second by a true intervertebral joint, increasing the number of joints in the lumbar spine from 5 to 6. It does not cause symptoms.

This is sideways curvature of the spine. It can be congenital, secondary to paralysis (such as poliomyelitis) or idiopathic (i.e. no known cause). As the curve increases, the ribs on the concave side are jammed together forcing the vertebrae to rotate. In turn this makes the ribs on the convex side more prominent causing a "hump back". Any type of scoliosis is often associated with premature aging changes in the discs at the apex of the curve. It can cause back pain. But in a recent survey of patients who had films of the abdomen made (usually looking for kidney stones) a considerable proportion had scoliosis with aging change but had no back symptoms. Thus in patients who have scoliosis and claim work related back symptoms, the facts must be interpreted with caution. 'Sciatic' scoliosis is sometimes seen in acute disc protrusions. It is not a structural deformity of the back but the result of muscle spasm.

This is an inflammatory arthritis that affects the spinal column, sacroiliac joints and sometimes the hips. It occurs almost exclusively in young males. Its cause is unknown. It produces fusion of the spinal column, sometimes in a flexed position so that victims of it have trouble seeing where they are going. It is characterized by intermittent flare ups of back pain often with leg radiation so that it can mimic a herniated disc. Eventually the process "burns out" leaving the patient with a stiff but painless spine. Although some authorities believe that trauma plays a role in its onset, the evidence is that it is not caused by trauma.

6) Conditions that a physician may erroneously consider being the cause of pain.

This is an abnormality of the growth plates that are on the upper and lower surfaces of the vertebral body before skeletal maturation. It can result in a marked increase in the normal rounding (kyphosis) of the thoracic spine in adolescents. It is seldom a cause of back pain: its principle effect is cosmetic. It is mentioned here because some physicians are puzzled by it.

These are indentations of the nucleus pulposus into the body of the vertebra above. They are normal and are never a source of pain.

Sometimes the growth plate (see Schuermann's disease above) fails to fuse completely to the vertebral body at the cessation of growth and appears in the x-ray as triangular piece of bone separated from the upper outer edge of the body. They are a variation of normal anatomy and do not cause symptoms.

7) Spinal tumors, both primary and metastatic, and inflammatory processes such as tuberculosis or osteomyelitis or discitis all cause back pain. They are readily diagnosed by appropriate imaging and with the rare exception of some cases of discitis or osteomyelitis are not caused by trauma.

Back pain may also be caused by an abnormality of organs in or behind the abdominal cavity.

There are a great many causes of back/leg pain and it is important that a careful diagnosis be made in each case before jumping to the conclusion the pain is necessarily due to work related activity or injury.

The majority of back pain is the result of a simple soft tissue (ligament and muscle) strain. The pain is in the low back. Commonly it radiates to one or both sides or to the buttocks and thighs. Nearly always it subsides spontaneously in a few days irrespective of the treatment. There is a growing consensus on two things: 1) that it is better for patients to keep active rather than going to bed and 2) there is no statistical evidence that treatment alters the rate of the normal spontaneous recovery.

When the pain results from a true disc herniation, it is in the low back and all the way down the leg (sciatica). The leg pain is worse than the back pain. It may be associated with numbness in the lower part of the leg or foot. The distribution of the leg pain depends on which disc is affected and hence which nerve root is compressed. With the 5th lumbar or 1st sacral root, the pain is in the buttock, back of the thigh, lower leg (shin or calf) and sometimes the foot and/or the toes. In the majority, the symptoms subside within a month or two and only rarely is surgery needed to remove the disc protrusion.

The symptoms of spinal stenosis are pain, numbness and weakness in the lower extremity(ies), brought on by walking or standing erect and relieved by flexing the spine (bending forward or sitting). There are usually no symptoms at rest. Once established the condition is permanent. Surgery to decompress the nerve roots may help.

In spondylolisthesis, pain is usually confined to the back although nerve root irritation caused by the instability of the adjacent bones may cause leg pain similar to that caused by a herniated disc. The pain is characteristically intermittent and brought on by activity. Most patients with x-ray evidence of spondylolisthesis have no symptoms. If treatment is needed the affected vertebra is fused (by bone grafting) with the one below.

Aging changes seen in plain x-rays, CT and MR scans are usually non symptomatic but aging (with or without imaging changes) can result in back pain.

Rarely. However, a severe injury, such as a fall from a height (as opposed to a lifting strain) may result in the appearance (within a year) of narrowing of a single disc with bony overgrowth (spurs or osteophytes) at the adjacent vertebral margins.

There is no evidence that the progression of x-ray changes is altered by a single injury (unless it is very severe) or by repetitive movement. However people with aging change might be more prone to develop back symptoms with repetitive strain although the evidence is tenuous. But it should be noted that as the age change progresses, the back becomes stiffer so that eventually the incidence of back pain diminishes.

Yes. When surgery is done for a herniated disc, it usually relieves the leg pain (sciatica) but patients commonly have grumbling intermittent back discomfort that persists for years. Thus if the surgery was required for a compensable condition, subsequent episodes of back pain may well be related to the compensable condition. But if the surgery was not compensable, subsequent episodes of back ache should be analyzed carefully: they are probably the result of the non-compensable condition.

Most patients go through their lives without symptoms. When pain occurs, it may come on spontaneously or it may follow a lifting strain or repetitive lifting. Once symptoms start, they tend to recur often without relation to the nature of the patient's activity. Spondylolysis and spondylolisthesis are usually preexisting and are probably not caused by trauma.

Yes. It is usually causally unrelated to the patient's activity, but activity may cause back pain in patients who have scoliosis. In work related claims for back symptoms, the facts must be interpreted with caution.

There is an extremely high incidence of abnormalities seen in spine imaging in people of all ages who have no symptoms. Evaluation of a patient with back pain and its possible relationship to work activity or injury requires thorough evaluation of the history and physical findings by a physician experienced in back problems and cautious in the interpretation of all the patient's imaging studies.