Low back pain causes countless visits to physicians, including 5% of all visits to family physicians. Two percent of the population consults a physician each year because of back pain. More than 80% of adults have had at least one episode of back pain, and many have had recurrent episodes since adolescence. It is the most common cause of disability in patients younger than age 45 years, and by age 50 years, 80% to 90% show evidence of degenerative disc disease at autopsy.
Despite the frequency of low back syndrome, it is poorly understood, physical examination is often unrewarding, and diagnostic test results are often negative or falsely positive. Some patients have local or radicular signs but no evidence of morphologic abnormalities, even after testing with all available diagnostic technologies. On the other hand, 50% to 60% of asymptomatic individuals have degenerative changes, and 20% have disc herniation without symptoms. To complicate matters even more, patients may change from one low back syndrome to another (e.g., from sciatica to chronic low back pain). Therefore, low back pain should be considered a symptom that is rarely attributable to a specific disease or pathologic lesion.
Low back pain most often has a mechanical origin. Mechanical causes include acute lumbosacral strain, postural backache, and degenerative lumbosacral arthritis, all of which may be caused by problems with muscles, tendons, ligaments, and discs. Other common causes are sciatica (often associated with a herniated disc), lumbar spinal stenosis, and chronic low back pain. Social and psychological factors are more pronounced in patients with chronic low back pain, and the severity of their symptoms does not match documented abnormalities.
Backaches in children are relatively uncommon., Backache represents serious disease more often in young children than in adults, although the most common cause of backache in children is lumbosacral sprain. This type of sprain usually results from participation in sports. A sprained back is occasionally caused by trauma (e.g., injuries sustained during a motor vehicle accident or during participation in gymnastics). Thoracic back pain and structural kyphosis in adolescents are usually caused by Scheuermann’s disease, a condition related to repetitive trauma in which the nucleus pulposus migrates through the cartilaginous layer between the vertebral body and the ring apophysis, resulting in its avulsion. The pain is located in the midscapular region.
Because low back pain may represent serious illness in children, a thorough history and physical examination should be performed. Infection should be a strong diagnostic consideration, especially in suspected intravenous (IV) drug users. Spondylolisthesis is a deficit in the pars interarticularis, which is the weakest part of the vertebra. It sometimes results in the anterior translocation of the affected vertebra, which is called spondylolysis Spondylolisthesis and spondylolysis occur more often in teenagers than in younger patients. Pain usually develops after strenuous athletic activity, and the cause can be detected best with single-photon emission computed tomography (SPECT), because plain radiographs may not detect an early stress fracture.
Regardless of the cause, backache is most common in patients between 20 and 50 years of age. It occurs more often in people such as industrial workers and farmers, who do heavy manual labor. In young adults who complain of persistent backache, nonbacterial inflammatory disease, such as Reiter’s syndrome and ankylosing spondylitis, should be considered. It is particularly important for the examiner to ask these patients about other inflammatory changes that may be associated with Reiter’s syndrome (e.g., iritis, pharyngitis, urethritis, arthritis). Even if the patient has spondylolisthesis, the physician must rule out inflammatory causes of backache. Postural backaches are more common in multigravida patients and individuals who are obese or otherwise in poor physical condition. Herniated discs occur in young adults but are relatively uncommon.
The number of backaches caused by disc disease rises as age increases from 25 to 50 years. Disc syndromes are more common in men, particularly older ones. In older patients, backache is a common symptom but not a common chief complaint. When it is the chief complaint in patients older than 50 years, serious illness such as lumbar spinal stenosis with or without cauda equina syndrome must be considered, although the most common cause is lumbosacral osteoarthritis. Everyone probably experiences some degenerative joint disease in the low back, but as a rule, clinical problems arise only when this degeneration reaches a moderate degree. It is then usually preceded by some traumatic incident, possibly minor, that precipitates the onset of symptoms. In patients older than 50 years who present with backache without a significant history of prior backaches, serious conditions such as cancer and multiple myeloma must be considered.
To determine the cause of backache, the physician must consider important historical factors, such as age, location of pain (Table 3-1) possible radiation of pain, effects of back or leg motion, and previous trauma.
The pain of acute lumbosacral strain is characterized by a sudden onset often related to turning, lifting, twisting, or unusual physical activity. It is usually well localized at the lumbosacral region.
The pain of a musculoskeletal strain and a postural backache is often described as dull and persistent and associated with stiffness. Patients have difficulty locating a precise point of maximum pain, although the pain is usually centered in the lower lumbar region. After trauma, this pain may have an immediate or delayed onset. Patients may state that they felt something “give way.” The pain typically radiates across the lower back and occasionally into the buttocks but rarely into the lower extremity. Radiation of pain does not always indicate nerve root compression.
The low back pain of degenerative lumbosacral arthritis has a gradual onset, is not usually precipitated by physical activity, and is usually associated with a history of morning stiffness. Many patients with this condition complain that their lumbosacral motion is limited by pain and stiffness that is often worse in the morning but improves an hour or so after they arise. Radiation of pain to the knee, calf, or lower leg is uncommon.
Many patients with herniated disc syndrome have a history of previous, less severe episodes. The pain usually has a sudden onset and often radiates into the buttock, down the posterolateral aspect of the leg, and sometimes to the foot. The pain of a disc syndrome has been compared with a toothache—sharp, lancinating, radiating pain that may be associated with paresthesias and muscle weakness (caused by nerve root pressure). Remitting pain usually indicates a posterolateral disc protrusion, but an intermittent backache can also be caused by a disc that does not produce significant root irritation. More than 90% of lumbar disc herniations occur at L4-L5 or L5-S1. If root irritation is present, neurologic findings (sensory loss, motor weakness, or hyporeflexia) are diagnostic. The patient may also have tenderness on palpation in the sciatic notch.
The qualitative characteristics of low back pain can be of considerable practical diagnostic importance. Variable, diffuse, and intense sensations of pressure often occur in patients without demonstrable organic disease. When the pain is described consistently and specifically, it is easier for the physician to demonstrate organic disease. Inflammatory disease (e.g., ankylosing spondylitis) and infectious processes (e.g., tuberculosis) are not likely if pain is related to posture, trauma, or overly strenuous activities, is episodic and intermittent, is aggravated by action, and is relieved by rest and recumbency.
Back pain in sacroiliac syndromes tends to be localized over the posterosuperior iliac spine. In sacroiliitis (inflammatory arthritis of the sacroiliac joints) the pain may alternate from side to side, although it is usually felt in the low back and buttocks and may radiate into the posterior thigh. The pain of sacroiliitis does not have a radicular distribution.
Occasionally, low back pain may be a manifestation of irritable bowel syndrome. In these cases, there is often associated midback pain, abdominal pain, and a history characteristic of an irritable colon. This pain does not radiate into the leg. The low back pain from prostatitis is usually a vague ache that is not affected by movement or coughing and is not associated with muscle spasm or limited mobility.
On rare occasions, the acute pain of renal colic manifests as excruciating pain in the back rather than in the flank or groin. The patient shows a gradual shift in the location of pain to the flank, with radiation into the groin. With renal colic the straight-leg raising test result is usually negative, and urinalysis generally shows hematuria.
Some patients with depression may experience chronic low back pain. It is often described as diffuse, accompanied by a sensation of severe pressure. When somatic pain is a manifestation of depression, the severity of the pain varies with the mental state: pain increases with anxiety and depression and often decreases with extreme fear. If an elderly patient describes a burning or aching back pain, particularly if it is superficial and unilateral, herpes zoster should be suspected, because this pain often precedes the herpetic skin lesions.
With lumbar osteoarthritis, patients often have pain in other joints. Patients with herniated disc syndrome usually have neurologic symptoms such as sciatica, paresthesias, dysesthesias, hypesthesias, anesthesias, paresis, sphincter problems, and impotence. Pressure on the unmyelinated fibers may cause cauda equina syndrome, a rare surgical emergency whose signs include central back pain associated with weakness of the leg muscles, impotence, urinary frequency, urinary retention (sometimes with overflow), incontinence, saddle anesthesia, and loss of sphincter tone.
Low back pain associated with vaginal discharge suggests a gynecologic cause. In men, back pain associated with burning on urination, difficulty in urination, or fever suggests prostatitis. If herpes zoster is associated with back pain, underlying cancer should be strongly considered.
The physician should be aware of the red flags of serious disease. Cancer or infection is suggested by unexplained weight loss, immunosuppression, urinary infection, IV drug use, prolonged use of corticosteroids, patient age more than 50 years, and back pain not improved with rest. Spinal fracture is suggested by a history of trauma, even minor trauma in osteoporotic elderly patients, or prolonged steroid usage. Cauda equina syndrome or some other severe neurologic compromise is suggested by acute urinary retention, overflow incontinence, loss of sphincter tone, saddle anesthesia, or progressive motor weakness in the lower limbs.