Muscle fibers or distal ligamentous attachments of the paraspinal muscles may tear, usually at the iliac crest or lower lumbar/upper sacral region. Resultant bleeding and spasm cause local swelling and marked tenderness at the site of injury. The patient typically presents after a specific episode of bending, twisting, or lifting. The strain is usually severe and is associated with a feeling of something giving way in the lower back. The onset of pain in the lower lumbar area is immediate. Pain radiates across the low back, often to the buttock and upper thigh posteriorly. Radiation of pain into the lower leg is rare because usually no injury to the nerve roots has occurred.

The pathophysiology of disk disease remains incompletely understood but involves degenerative changes in the disk. It is
believed that degeneration and attritional changes in the lower lumbar disks are caused by the concentration of stress at the lumbosacral level. Stresses resulting from the enormous longitudinal and shear forces that are a consequence of upright posture are aggravated by bending strain. Injury, inflammation, weakening, and tear of the disk annulus may occur and lead to localized back pain (so-called discogenic pain). Pain receptors in the longitudinal ligaments probably mediate the recurring attacks of local back pain, which are nonradicular and most pronounced with prolonged sitting. Eventually, the disk may become so weakened that it bulges circumferentially beyond the disk interspace. Less often, a focal or asymmetric extension beyond the interspace, termed a disk protrusion, develops. Extreme extension of the disk beyond the interspace has been called extrusion. Historically, the term herniation has been used to describe all these phenomena. It has been suggested that the use of the more specific terms will sharpen our understanding of the relationship between disk disease and pain syndromes. Regardless of the vocabulary, compression and irritation of a lower lumbar or upper sacral nerve root may result, and the radicular symptoms of sciatica develop.

Sciatica is the symptomatic hallmark of nerve root irritation. Disk protrusion or extrusion is present in 95% of cases. It presents as sharp or burning pain radiating down the posterior or lateral aspect of the leg to the ankle or foot (depending on the specific nerve root involved). The pain may be worsened by cough, Valsalva maneuver, or sneezing, and it is often accompanied by paresthesias and numbness. Weakness may also develop in the areas supplied by the irritated nerve root.

More than 95% of disk protrusions and extrusions occur at L4 to L5 or L5 to S1, with the L5 and S1 nerve roots affected, respectively. With S1 root irritation, pain, numbness, and paresthesias involve the buttock, posterior thigh, calf, lateral aspect of the ankle and foot, and lateral toes. Calf atrophy can occur, the ankle jerk can be diminished or absent, and plantar flexion weakness may be noted. With L5 root compression, pain radiates to the dorsum of the foot and great toe, and the only neurologic deficits may be extensor weakness of the great toe and numbness of the L5 area on the dorsum of the foot at the base of the great toe (Fig. 147-1). In the rarer instance of high lumbar disk disease, pain radiates to the anterior thigh, and the knee jerk may be diminished or absent. Quadriceps atrophy and weakness may be found.

With lower lumbar disk disease, especially disk extrusion, lumbar paraspinal muscle spasm often occurs and limits lumbar motions. A list away from the side of the disk extrusion—socalled sciatic scoliosis—may develop, and often tenderness of the lower lumbar spine and sciatic notch is present. Straight-leg raising (SLR) on the affected side is limited by back and leg pain that increases on ankle dorsiflexion at the extreme of the maneuver. With upper lumbar disk disease, reverse SLR often reproduces the back and anterior thigh pain (see later discussion).

The clinical course may begin with a several-year history of recurring mild mid-low back pain related to minor back strain, with symptoms clearing spontaneously within a few days. Attacks typically increase in frequency and severity at intervals of several months to several years. Finally, an episode of persistent pain accompanied by sciatica develops, often triggered by a seemingly trivial stress (e.g., bending over in the shower to pick up the soap).

This often-overlooked etiology is becoming better appreciated as an important cause of chronic low back and lower extremity complaints. It occurs predominantly in elderly individuals with osteoarthritic spurring, chronic disk degeneration, and facet joint arthritis. Spinal stenosis is also found in young people who have a congenitally narrowed lumbar spinal canal. In either case, the changes narrow the canal and the neuroforamina, leading to root impingement and pain.

The characteristic symptom is pain that is worsened by standing, walking, or other activities that cause spinal extension and is relieved by rest, especially by sitting or lying down and flexing the spine and hips. Patients report pain in the low back, gluteal region, or lower extremities; often, it is bilateral. Numbness or weakness may accompany the pain in the legs. Because symptoms are often worsened by walking and relieved by sitting down and resting, they can mimic vascular insufficiency and are sometimes referred to as pseudoclaudication.

On examination, the spine demonstrates good range of motion and little focal tenderness. SLR is usually normal. Minor neurologic deficits (e.g., a diminished ankle jerk) may be present, but no pattern is characteristic.

The natural history of the condition is generally favorable, with only 15% of patients reporting clinical worsening over 5 years; 70% stay the same and 10% improve. Cauda equina syndrome is very rare in spinal stenosis.

The term denotes forward subluxation of a vertebral body. In adults, the condition results from degenerative changes and arthritis of the facet joints, usually at L4 to L5 or L5 to S1, with forward slippage of 10% to 20% of the diameter of the vertebral body. About 70% of patients with spondylolisthesis have chronic low back pain; sciatica is infrequent. The pain is caused by strain imposed on the ligaments and intervertebral joints.

The seronegative spondyloarthropathies (which include ankylosing spondylitis, psoriatic arthritis, reactive arthritis, and arthritis associated with inflammatory bowel disease) have both peripheral and axial skeleton manifestations. There is considerable overlap among these inflammatory joint diseases, which
share involvement of the sacroiliac joints and axial skeleton, limb joints, and entheses (sites of insertion of ligaments and tendons [e.g., Achilles, patellar, plantar fascia] into bone), as well as nonarticular sites (e.g., uveal tract, skin, bowel, and aortic valve). Focal tenderness may be reported at sites of involvement. A relation to mechanical stress has been invoked to explain the distribution of findings. There is a strong association with HLA-B27 positivity, suggesting an immune pathophysiology; rheumatoid factor is negative. Male predominance is the rule.

Ankylosing spondylitis is the most common of these conditions. Its characteristic features helpful for diagnosis include low back pain of at least 3 months’ duration, improvement with exercise but not with rest, limitation of lumbar spine motion and chest expansion, and bilateral sacroiliitis or severe unilateral disease. Spinal involvement is most prominent in young men; onset is gradual. Morning spinal stiffness is typical. Spinal radiographic findings are often unremarkable in the early phases, but films of the sacroiliac joints may show narrowing of the joint space and reactive sclerosis (“sacroiliitis”). Eventually, the sacroiliac joint space becomes obliterated, and fusion follows. Squaring of the vertebral bodies is the first spinal radiologic manifestation, followed by the development of syndesmophytes. Similar although less florid changes may occur in the other seronegative spondyloarthropathies.

In normal bone, this fracture requires severe flexion-compression force. It is acutely painful. Spontaneous vertebral body collapse, or pathologic fracture, is most commonly seen in elderly persons with severe osteoporosis (see Chapter 164), in patients taking long-term glucocorticoids (see Chapter 105), and in cancer patients with lytic bony metastases. Usually, the history is one of sudden back pain brought on by a minor stress. The discomfort is noted at the level of fracture, with local radiation across the back and around the trunk, but rarely into the lower extremities. The fracture is more likely to occur in the middle or lower levels of the dorsal spine, which helps to differentiate the problem from lumbar disk herniations, 95% of which occur at the level of the L4 or L5 disk.

The most common spinal tumor is metastatic carcinoma. Breast, lung, prostate, gastrointestinal, and genitourinary neoplasms commonly metastasize to the spine. Purely lytic lesions, which are often caused by renal or thyroid carcinoma, are seen occasionally. Myeloma is the most common primary bone tumor involving the spine. About 80% of patients are older than 50 years of age.

Typically, metastasis is hematogenous to the marrow of the vertebral bodies. Involvement of the periosteum and bony destruction lead to pain, and extension to the spinal cord can produce neurologic deficits. The disk spaces are usually spared, and disk space height is maintained, helping to differentiate the condition from degenerative disease. Collapse of the vertebral body as a result of bony destruction may be difficult to differentiate from compression fracture if osteoporosis is present. Extension into the epidural space or vertebral body collapse can lead to spinal cord compression; vascular compromise by the tumor may also contribute to cord injury.

Although only 30% of persons with metastatic disease as the cause of back pain give a history of previous cancer, in those that do, the probability of spinal metastasis is high. Approximately 90% report night pain and pain unrelieved or worsened by lying down or bed rest. A history of prior malignancy, insidious increase in pain in a region atypical for disk disease (e.g., the midback), and failure to obtain relief by lying down are highly predictive of metastatic tumor.

The clinical presentation is one of insidious onset of back pain, gradually increasing in severity and aggravated by activity and lying down. Location can be anywhere in the spine, but occurrence in an area atypical for degenerative disk disease (e.g., the midback) is suggestive. A hallmark is back pain worsened by activity and worsened, or at least not relieved, by lying down. There may be focal spinal tenderness. Extension into the epidural space is heralded by increasing back pain followed by neurologic symptoms a few weeks to months later. Besides back pain, manifestations of epidural invasion include upper motor neuron signs (proximal muscle weakness, hyperreflexia, upgoing toes), sensory loss in a dermatomal distribution, and autonomic dysfunction (urinary retention, fecal incontinence). Prognosis is poor without early intervention.

Intraspinal tumors may present in the same manner as do herniated disks. However, marked progression of neurologic deficits despite adequate conservative therapy is a clue to the existence of a tumor inside the spinal canal. Extraspinal tumors may eventually cause root impingement and simulate discogenic sciatica. Tumors of the retroperitoneum, pelvis, and large bowel may extend to the roots. This is a very late development; metastases may occur earlier.

Back pain resulting from infection is rare but important to detect. An identifiable source is found in 40% of cases; possibilities include urinary tract infection, skin abscess, indwelling catheter, and intravenous drug abuse. Vertebral osteomyelitis is usually hematogenous in origin but may occasionally result from a spinal procedure, such as lumbar puncture, myelography, diskography, or disk surgery. In addition to involving the vertebral bodies, it may extend into the disk space, producing a very painful diskitis. In the absence of diskitis, the presentation is typically one of dull, continuous back pain, often in conjunction with low-grade fever and spasm over the paraspinous muscles. Tenderness to percussion over the involved vertebrae is common, but fever and elevated white cell count are absent in up to half of cases. A compression fracture or an epidural abscess may ensue. Staphylococcus aureus accounts for about 60% of bacterial cases and enterobacteria for 30%.

Epidural abscess develops in the context of bacteremia or osteomyelitis. The infection presents as back pain, focal tenderness, and fever. Fever and spinal tenderness are present in about 85% of cases. If the condition is not promptly treated, it may extend to compromise the local blood supply to the spinal cord and rapidly progress from spinal ache to major motor and sensory deficits within hours to a few days.

Patients with depression may present complaining of chronic low back pain. Often, they have a history of previous back problems or onset at the time of a minor injury, with the depression amplifying the presentation and prolonging the clinical course. Mild muscle spasm may be noted on physical examination. Characteristically, the intensity of the symptoms and the degree of disability are much greater than the minor limitations found on examination would suggest. Multiple somatic symptoms are common (see Chapter 227). Other patients may have an underlying somatization disorder. Many of these patients appear refractory to therapy and are often unwilling to take an active role in their treatment. Some even seem to derive a sense of legitimacy and self-worth from their suffering (see Chapter 230).

Malingering implies conscious deception for the sake of obtaining gain from being ill. Inconsistencies among symptoms and physical findings typify the malingerer. These often can be brought out by distracting the patient.

Although the spinal cord ends at the L1 level, the collection of nerve roots that make up the cauda equina is subject to injury by any process that compromises the spinal canal below the L1 level. Massive midline disk herniation is the most common cause of cauda compression and a serious, although very infrequent, event that requires prompt attention. In contrast to the clinical presentation of simple root impingement, the presentation in cauda equina syndrome includes urinary retention in almost 90% of cases. Another characteristic feature is saddle anesthesia (a reduction in sensation over the buttocks, upper posterior thighs, and perineum), which is reported by about 75% of patients. Both of these clinical findings are a consequence of sacral root compression, as is a decrease in anal sphincter tone, which is noted in about two thirds of cases. Sciatica and lower extremity motor and sensory deficits are prominent and often bilateral. Patients may report falling.

In elucidating the basic features of back pain (i.e., quality, location, onset, radiation), one should also inquire specifically into symptoms that are potentially indicative of serious underlying disease (e.g., fever, progressive neurologic deficits, bilateral deficits, bladder dysfunction, saddle anesthesia, persistent pain unresponsive to bed rest or worsened by lying down). A history of recent injury and a prior history of cancer are other critical elements to be noted, as are previous therapy for back problems, recent lumbar puncture, concurrent infection, and prolonged use of high-dose corticosteroids. The presence of sciatica helps to narrow the differential diagnosis (see Table 147-1).

Aggravating and alleviating factors may have important diagnostic significance. Morning stiffness in the back that is relieved by activity suggests ankylosing spondylitis or other inflammatory conditions. Worsening or onset of symptoms with standing or walking and relief with bending or sitting is characteristic of spinal stenosis, whereas worsening with sitting, driving, or lifting points to lumbar disk herniation. Malignancy is suggested by pain in a location atypical for degenerative disease (e.g., the midback) as well as by pain in any location that is worsened not only with activity but also on lying supine.

Associated symptoms are critical to check for, especially fever (raising the question of epidural abscess) and neurologic deficits (suggestive of cord or root injury). Is there any difficulty in standing or climbing stairs, urinating, or maintaining fecal continence? Is there truncal or saddle anesthesia? If so, a high index of suspicion is required for cord or cauda equina injury. Typical unilateral root symptoms (pain, numbness, weakness) in a characteristic lumbosacral root distribution suggest root impingement, but bilateral radicular symptoms, especially if severe and new in onset or rapidly progressive, should raise concern about cauda equina syndrome or epidural injury.

The patient should be asked to describe the effect of the back pain on daily activities. Emotional and social stressors are sought if the severity and duration of the symptoms appear to be disproportionate to the amount of organic disease present. Under such circumstances, it is important to check for depression (see Chapter 227) and manifestations of somatization disorder (see Chapter 230).

For the majority of patients with low back pain, a careful history and a physical examination usually suffice for diagnosis at the time of the initial office visit. The utility of imaging studies is limited to a few specific situations, many of which are also indications for referral or consultation (see later discussion).