The importance of back and neck pain in our society is underscored by the following: (1) the annual societal cost of back pain in the United States is estimated to be between $20 and $50 billion; (2) back symptoms are the most common cause of disability in patients under 45 years of age; (3) 50% of working adults, in one survey, admitted to having a back injury each year; and (4) approximately 1% of the U.S. population is chronically disabled because of back pain.
The enormous economic pressure to provide rational and efficient care of patients with back pain has resulted in clinical practice guidelines (CPGs) for these patients. CPGs are algorithms which guide evaluation or treatment at specific steps in patient care. CPGs for acute low back pain (ALBP) are based upon incomplete evidence (see algorithms, Fig. 16-6) but represent an attempt to standardize common medical practice. Major revisions in CPGs for back pain can be anticipated in the future. Management of patients with chronic low back pain (CLBP) is complex and not amenable to a simple algorithmic approach at this time.
Anatomy of the Spine
The anterior portion of the spine consists of cylindrical vertebral bodies separated by intervertebral disks and held together by the anterior and posterior longitudinal ligaments. The intervertebral disks are composed of a central gelatinous nucleus pulposus surrounded by a tough cartilagenous ring, the annulus fibrosis; disks are responsible for 25% of spinal column length . The disks are largest in the cervical and lumbar regions where movements of the spine are greatest. The disks are elastic in youth and allow the bony vertebrae to move easily upon each other. Elasticity is lost with age. The function of the anterior spine is to absorb the shock of typical body movements such as walking and running.
The posterior portion of the spine consists of the vertebral arches and seven processes. Each arch consists of paired cylindrical pedicles anteriorly and paired laminae posteriorly . The vertebral arch gives rise to two transverse processes laterally, one spinous process posteriorly, plus two superior and two inferior articular facets. The functions of the posterior spine are to protect the spinal cord and nerves within the spinal canal and to stabilize the spine by providing sites for the attachment of muscles and ligaments. The contraction of muscles attached to the spinous and transverse processes produces a system of pulleys and levers that results in flexion, extension, and lateral bending movements of the spine. Normal upright posture in humans places the center of gravity anterior to the spine. The graded contraction of well-developed paraspinal muscles attached to the laminae, transverse processes, and spinous processes is necessary to maintain normal upright posture.
The nerve roots exit at a level above their respective vertebral bodies in the cervical region (the C7 nerve root exits at the C6-C7 level) and below their respective vertebral bodies in the thoracic and lumbar regions (the T1 nerve root exits at the T1-T2 level). The spinal cord ends at the L1 or L2 level of the bony spine. Consequently, the lumbar nerve roots follow a long intraspinal course and can be injured anywhere from the upper lumbar spine to their exit at the intervertebral foramen. For example, it is common for disk herniation at the L4-L5 level to produce compression of the S1 nerve root (Fig. 16-3). In contrast, cervical nerve roots follow a short intraspinal course and exit at the level of their respective spinal cord segments (upper cervical) or one segment below the corresponding levels (lower cervical cord). Cervical spine pathology can result in spinal cord compression, but lumbar spine pathology cannot.
Types of Back Pain
An understanding of the nature of the pain as described by the patient is the essential first step in evaluation. Attention is also focused on identification of risk factors for serious underlying diseases that require specific evaluation.
Local pain is caused by stretching of pain-sensitive structures that compress or irritate sensory nerve endings. The site of the pain is near the affected part of the back.
Pain referred to the back may arise from abdominal or pelvic viscera. The pain is usually described as primarily abdominal or pelvic but is accompanied by back pain and usually unaffected by posture. The patient may occasionally complain of back pain only.
Pain of spine origin may be located in the back or referred to the buttocks or legs. Diseases affecting the upper lumbar spine tend to refer pain to the lumbar region, groin, or anterior thighs. Diseases affecting the lower lumbar spine tend to produce pain referred to the buttocks, posterior thighs, or rarely the calves or feet. Provocative injections into pain-sensitive structures of the spine (diskography) may produce leg pain that does not follow a dermatomal distribution. The exact pathogenesis of this "sclerotomal" pain is unclear, but it may explain many instances in which combined back and leg pain is unaccompanied by evidence of nerve root compression.
Radicular back pain is typically sharp and radiates from the spine to the leg within the territory of a nerve root (see "Lumbar Disk Disease," below). Coughing, sneezing, or voluntary contraction of abdominal muscles (lifting heavy objects or straining at stool) may elicit the radiating pain. The pain may increase in postures that stretch the nerves and nerve roots. Sitting stretches the sciatic nerve (L5 and S1 roots) because the nerve passes posterior to the hip. The femoral nerve (L2, L3, and L4 roots) passes anterior to the hip and is not stretched by sitting. The description of the pain alone often fails to distinguish clearly between sclerotomal pain and radiculopathy.
Pain associated with muscle spasm, although of obscure origin, is commonly associated with many spine disorders. The spasms are accompanied by abnormal posture, taut paraspinal muscles, and dull pain.
Back pain at rest or unassociated with specific postures should raise the index of suspicion for an underlying serious cause (e.g., spine tumor, fracture, infection, or referred pain from visceral structures). Knowledge of the circumstances associated with the onset of back pain is important when weighing possible serious underlying causes for the pain. Some patients involved in accidents or work-related injuries may exaggerate their pain for the purpose of compensation or for psychological reasons.