Back Pain

I

Introduction

Back Pain, a common condition characterized by pain in a region along the spinal column, often in the lower portion of the back.

II

Anatomy of the Back

The spinal column is the main supporting structure in the human body. It consists of a chain of 33 bones called vertebrae standing in a stack, one on top of the other. Each vertebra is joined to the one above and below by joints and ligaments. In between each vertebra lies a cushion of spongy tissue called an intervertebral disk. The intervertebral disks act as shock absorbers for the spine. Each disk consists of a central area known as the nucleus pulposus and an outer ring known as the annulus fibrosus. The nucleus pulposus contains a flexible jelly-like material that accommodates the various stresses imposed on the spine. Its shape is maintained by the outer annular ring and by the vertebrae above and below it. Along the vertebral column, nerves emerge from between the vertebrae through gaps called intervertebral foramina and travel outward to various parts of the body.

III

Back Disorders

Disorders of the spine that can lead to back pain include injury; mechanical and structural defects; inflammatory disorders, such as rheumatoid arthritis; and, much more rarely, tumors that occur in and around the back. In some cases no cause for the pain can be found despite extensive investigation.

One of the most common causes of back pain is a herniated intervertebral disk, commonly referred to as a “slipped disk.” In this often very painful condition, the disk bursts or ruptures, and fragments of the outer annulus fibrosus, together with some of the inner nucleus pulposus, press on ligaments and nerves that run close to the spine. The disk protrudes outward but does not actually “slip.” Although any disk in the spine can herniate, or burst, the lowest five are most commonly affected. The lower vertebrae are under the greatest mechanical stress because they support most of the body’s weight, whereas the upper vertebrae support the weight of the head only. If the protruding disk presses on one or more of the nerves which emerge from the intervertebral foramina, sensations of pain, numbness, and tingling are felt in the anatomical area supplied by that nerve. If the sciatic nerve is affected, pain radiates through the lower back and buttock into the legs, a condition called sciatica.

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Although a herniated disk can occur at any age, it is most frequent between the ages of 20 and 50 years, with the peak incidence being between 40 and 45 years. The pain may strike immediately or it may develop gradually over hours or days. In severe cases, it may prevent the patient from standing or straightening up. The back itself will usually show a sharp twist. This twisting of the spine is a reflex compensatory mechanism by which the body tries to relieve some of the pressure on a trapped nerve. Depending on severity, attacks of back pain due to rupture of an intervertebral disk may subside with immediate rest and treatment over several days to several weeks.

One of the most common causes of back pain is wear-and-tear damage to the spine. With age, the disks lose their flexibility and are gradually replaced by fibrous tissue. At the same time, the bony surfaces of the vertebrae and the intervertebral joints begin to degenerate. The bony ends of the vertebrae become thickened and a rim of bony tissue develops around the edge of the disk. These changes, termed spondylosis, are the body’s attempt to prevent further damage by splinting the spine in position. Damage to the small joints between the vertebrae produces the condition known as osteoarthritis. By the age of 60, the spines of most people show signs of wear-and-tear damage, which can be seen on X rays. These changes are an inevitable consequence of aging. Symptoms include pain and stiffness in the back, with consequent restriction of movement, so that the patient can no longer bend down, or can only do so with a certain amount of pain.

Strains and sprains in the joints located in and around the vertebral column cause back pain that is usually localized to the affected area. If the strain has been severe, the affected ligaments may heal by forming fibrous tissue, which leads to impaired mobility. Back strain that occurs while lifting heavy objects may cause a stiff back for years afterward.

Very low back pain is usually due to problems with the sacroiliac joints. These joints connect the sacrum, located at the very base of the vertebral column, to the ilium, or hip bone. Inflammation of these joints leads to a condition known as ankylosing spondylitis, which produces severe stiffening and impaired mobility. The end result is a “bamboo spine,” so-called because all the vertebrae eventually become fused together, resulting in a completely rigid spine. This condition most often appears in young men between 15 and 25 years of age and is thought to affect around 2 percent of the population. Regular exercise and physical therapy can prevent the progression of this disease.

Bone diseases may also give rise to back pain. The most common conditions associated with this kind of back pain are osteoporosis and osteomalacia. These diseases are caused by insufficient calcium or vitamin D. Progressive weakening of the bones in either of these conditions may result in crush fractures, when one of the vertebrae of the backbone collapses because it can no longer support the weight of the body. This usually causes sudden, severe back pain from pressure created by the fracture on the nerves around the spine, and typically requires immediate surgery.

Tumors of the spine are rare and an uncommon cause of back pain. They may be due either to growths spontaneously generated in that area, or to the spread of cancer from elsewhere in the body. Determining whether a tumor is benign or malignant usually requires a biopsy.

A

Diagnosis of Back Pain

Physicians diagnose back pain based on the symptoms described by the patient. X rays are nearly always performed and are useful for examining the bony structure of the vertebral column. X rays can only visualize bony structures and are of little use for looking at the disk itself. More sophisticated investigative techniques, such as computed tomography (CT) scans or magnetic resonance imaging (MRI) scans, are necessary to visualize accurately the intervertebral disks and the soft tissues of the back. It is then possible to see if the disk has ruptured, and if it has, whether it is pressing on a nerve root. Some specialists will diagnose types of disk lesions by analyzing the various movements made by the patient.

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