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Lower Back Pain

About Lower Back Pain

Low back pain is a common disorder affecting millions of individuals annually. Back pain is the single most common cause for lost workdays in the United States and one of the most common reasons for patients to visit their primary care physician. It is estimated that approximately 60 to 80% of the adult population suffers from a memorable episode of low back pain each year.

In the vast majority of cases no specific diagnosis is made and the symptoms resolve spontaneously. Only a minority of patients present with symptoms specific to an irritated nerve root or have identifiable pathology on radiographic studies. The overall prognosis of low back pain is good, with improvement occurring in the majority of cases without aggressive medical intervention.

In order to understand the principles of low back pain a basic knowledge of spinal anatomy is helpful. The spine is made up of 24 to 25 separate bones known as the “vertebrae”. The basic functioning unit of the spine is known as the “spinal motion segment,” composed of two adjacent vertebral bodies, the intervening intervertebral disc, and surrounding ligaments. The portion of the spine that is equivalent to the lower back is referred to as the Lumbar Spine.

The vertebral bones articulate through three joints, two “facet joints” along the back of the spine and the intervertebral disc. The intervertebral disc and facet joints are densely supplied by nerve fibers that play an important part in the various clinical manifestations of back pain.

The vertebral bodies form a bony canal that runs the entire length of the spine and contains the spinal cord and associated nerves. The spinal cord acts as a relay, transmitting information between the brain and remainder of the body. At each spinal motion segment a pair of “spinal nerves” exit to supply various parts of the body. These nerves are in close proximity to both the intervertebral disc and facet joints.

Symptoms of Lower Back Pain

Degenerative changes involving these structures can irritate the exiting nerves and produce symptoms within the area supplied by the nerve, known as a “Radiculopathy.” When the nerves of the lower back are involved these symptoms are referred to the legs and are commonly referred to as “Sciatica.”

The intervertebral disc plays an important role in the degenerative cascade that can eventually lead to low back symptoms. The normal disc is composed of a fibrous ring of tissue containing a gelatinous center that acts to cushion the vertebral bones and limit the degree of normal motion. As a result of the aging process, the fluid content within the disc interior decreases, leading to a transformation from a gelatinous central core to one composed of dry, stiff, fibrous tissue.

The outer fibrous ring also deteriorates with age, developing tears and allowing migration of the internal tissues beyond the normal confines of the disc space. These changes all contribute to structural changes that eventually lead to mechanical incompetence of the disc.

Over time, degenerative changes to the spinal motion segment, compounded by any additional stresses and trauma, can lead to an abnormal transfer of stress across the degenerated spinal segment and produce “Mechanical Pain”. Collectively these degenerative changes are referred to as “Spondylosis”, the medical term for arthritic spinal disease.

Causes and Treatments of Low Back Pain

Any anatomical element of the spine may be a source for pain. The intervertebral disc, facet joints, surrounding ligaments, and muscles adjacent to the spine are all innervated by nerve fibers that relay pain information and can individually or collectively contribute to the generation of low back pain. Attempts have been made to characterize specific pain patterns produced by abnormalities of these structures, however to date there is no standardized method of categorizing, diagnosing, or treating many of the pain syndromes described.

Pain originating from the ligaments and muscles surrounding the spine has been categorized as Myofascial Pain. This type of pain is usually caused by excessive strain to the ligaments or muscles and is prolonged through mechanical factors.

The pain is typically in an ill-defined area but can usually be reproduced in individual patients with specific maneuvers of the lower back. These patients are typically treated with activity modification, physical therapy, and a course of non-steroidal anti-inflammatory drugs (NSAIDS).

Abnormalities of the spine, either the vertebrae, intervertebral disc, or associated joints, are thought to produce pain referred to as Mechanical Back Pain. The pain is thought to originate from stress or strain placed on a degenerative joint. Various syndromes have been named in an attempt to define the origin of pain including the “Facet Syndrome,” for pain originating from the facet joints, and “Discogenic Back Pain,” for pain originating from the intervertebral disc. Despite the different syndromes described, there are no specific diagnostic tests to make this distinction.

The pain produced is often described as a dull ache that originates in the midline and radiates into the hip, buttocks and/or thighs. The pain is typically exacerbated by activity, hyperextension, or prolonged standing and relieved with rest or lying flat. Typically there are no sensory changes or muscle weakness associated with mechanical back pain.

Treatment options include conservative maneuvers, such as physical therapy and NSAIDS. Surgery is reserved for symptoms that do not respond to conservative therapy and produce debilitating pain.