INTRODUCTION — Back pain is the second most common symptom-related reason for clinician visits in the United States [1]. Up to 84 percent of adults have low back pain at some time in their lives [1,2].
The spectrum of illness and morbidity associated with low back pain is broad. For many individuals, episodes of back pain are self-limited and resolve without specific therapy. For others, however, back pain is recurrent or chronic, causing significant pain that interferes with employment and quality of life. Rarely, acute back pain is a harbinger of serious medical illness, including infection, malignancy, or other systemic disease.
This discussion will focus on an approach to the initial evaluation of a patient presenting with low back pain. Diagnostic tests for low back pain and the treatment of acute, subacute, and chronic low back pain are discussed separately. (See "Diagnostic testing for low back pain" and "Treatment of acute low back pain" and "Subacute and chronic low back pain: Pharmacologic and noninterventional treatment" and "Subacute and chronic low back pain: Nonsurgical interventional treatment" and "Subacute and chronic low back pain: Surgical treatment".)
EPIDEMIOLOGY — In a 1989 to 1990 US survey, back pain accounted for approximately 2.5 percent of medical visits, resulting in 15 million office visits [3]; the percent of office visits due to back pain was essentially the same in 2002 [4].
The prevalence of back pain has been estimated in multiple surveys, representing different populations and different definitions:
The total costs of low back pain in the United States exceed $100 billion per year [10]. Seventy-five percent of the total cost is attributable to fewer than 5 percent of the patients with low back pain.
Back pain has a substantial impact on lifestyle and quality of life. One US survey found that 72 percent of those who sought treatment for back pain gave up on exercising or sports-related activities. Sixty percent said they were unable to perform some daily activities, and 46 percent said they had given up sex because of their back condition [11].
Risk factors — Risk factors for the onset of back pain include smoking, obesity, older age, female gender, physically strenuous work, sedentary work, psychologically strenuous work, low educational attainment, Workers' Compensation insurance, job dissatisfaction and psychological factors such as somatization disorder, anxiety, and depression [2,7,10,12,13].
A population-based, prospective study in England found that physical activity outside the workplace was not associated with back pain, but that poor physical health in both men and women, and heavier weight in women, increased the risk of new back pain [14]. The same study found that jobs involving lifting, pulling, or pushing objects of at least 25 pounds, and jobs involving prolonged periods of standing or walking, were associated with a higher incidence of low back pain, especially among women [15].
Prospective studies have found that psychosocial variables strongly predicted both long-and short-term disability, but structural spine changes were only weakly associated with adverse outcomes [16,17]. In addition, twin studies indicate that genetic factors are associated with the development of degenerative changes on imaging [18]. Additionally, cultural differences may influence the perception of low back pain. As an example, a cross-sectional study, using multivariate analysis to adjust for potential confounders, found that the risk of back pain in West Germany was 2.5 to 3.5 times higher than in the United Kingdom [19].
Prognosis — The long-term outcome of low back pain is generally favorable. In one prospective study, 90 percent of patients seen for low back pain in primary care did not seek care after three months [20]. However, most patients were still experiencing low back pain, for which they did not seek care, one year after the initial episode.
Patients who have high expectations for recovery have better outcomes. A secondary analysis of a randomized trial comparing usual care to chiropractic care, acupuncture, or massage in adults with acute low back pain showed that higher expectations for recovery were associated with greater functional improvement at 12 week follow-up [21]. MRI evaluation to provide reassurance, however, does not lead to better prognosis [22].
A longitudinal study of 973 primary care patients with recent onset low back pain found that 83 percent had mild or no pain and 86 percent had minimal or no disability at one year follow-up; however, only 72 percent had completely recovered [23]. It should be noted that cross-sectional sampling of patients from clinical practices over-represents patients with recurrent pain, and these findings may not be applicable to the general population with low back pain. Indeed, 75 percent of the patients in this study reported previous back pain episodes, 39 percent had previous sick leave for back pain, and 19 percent had been involved in compensation claims.
Psychosocial variables are stronger predictors of long-term disability than anatomic findings found on imaging studies. In a systematic review of 20 prospective studies in patients presenting with acute low back pain, predictors of disabling chronic low back pain at one year follow-up included maladaptive pain coping behaviors, functional impairment, poor general health status, presence of psychiatric comorbidities, or nonorganic signs [24]. (See 'Nonorganic signs or Waddell's signs' below.)
TERMINOLOGY — Several terms are used to describe conditions related to the back, based upon radiological findings (spondylosis, spondylolisthesis, spondylolysis), physical findings (lumbar lordosis, kyphosis, scoliosis), and clinical or neurologic features (neurogenic claudication, radiculopathy, sciatica, cauda equina syndrome). These terms are defined in a table (table 1). There are also clinical entities that have been associated with low back pain symptoms that are either hard to reliably diagnose or are not clearly associated with symptoms, including the piriformis syndrome, "back mouse," annular tears, and sacroiliac joint dysfunction.
The piriformis syndrome is thought by some to be a condition in which the piriformis muscle, a narrow muscle located in the buttocks, compresses or irritates the sciatic nerve [25,26]. There is debate in the medical community whether this is a discrete condition, since it lacks objective evidence and therefore cannot be reliably assessed.
The "back mouse," a term for a fibro-fatty nodule, has been proposed as a cause of low back pain [27], although only case reports exist and its correlation with back pain is unproven. Older case reports describe findings of fat herniation through a fascia just above the iliac crest in patients, mostly young athletic women, who complained of a tender mass [28].
Annular tears are tears or fissures of the annulus fibrosus of the intervertebral disk, typically discovered on MRI. It is not clear that annular tears are clinically relevant since several small studies found no correlation between the presence of annular tear and back pain [17,29,30]. As an example, a prospective study of asymptomatic patients found that 38 percent had evidence of annular tears at baseline [31]. Follow-up after three years showed that annular tears were not associated with new back pain [17]. Thus, given available data, these imaging findings appear to have little clinical importance.
"Sacroiliac joint dysfunction," a term to describe pain in the region of the sacroiliac joint believed to be due to malalignment or abnormal joint movement, is a controversial topic. Tests of pelvic symmetry or sacroiliac joint movement have been shown to have low intertester reliability [32-38] and provocative maneuvers such as fluoroscopically guided injections of the sacroiliac joint have been unreliable in diagnosis and treatment [37,39]. The sacroiliac joint may be a referred site of pain, including from a degenerative disc at L5-S1, spinal stenosis, or osteoarthritis of the hip.
CLINICAL EVALUATION — Low back pain is often attributed to disc degeneration, which is the primary target for many diagnostic approaches (figure 1) [40]. However, the importance of imaging findings associated with disc degeneration (osteophytes, disc narrowing, and herniation) remains unclear. Muscular and ligamentous sources of pain may be equally important.
Although the differential diagnosis of low back pain is broad (table 2), the vast majority of patients seen in primary care will have "mechanical" or non-specific low back pain, meaning that there is no neoplastic, infectious, or primarily inflammatory cause [40]. Among all primary care patients with low back pain, less than 5 percent will have serious systemic pathology. Although patients are often told a specific diagnosis for their back pain, reproducibility of these diagnoses (ie, muscle spasm, sacroiliac pain, trigger points) among providers is poor [32,33,41,42].
Diagnostic uncertainty exists even for those with back symptoms and well-described findings on scan, as these findings are common even in subjects without back pain, and may be unrelated to the symptoms. As an example, herniated disks can be identified in significant numbers of CT or MRI low back studies in subjects with no back pain. (See 'CT and MRI scanning' below.)
In discussing the cause of a patient's back symptoms, clinicians should avoid using terms that imply deteriorating or damaged body parts. Patients may associate such labels with frightening mental images and serious abnormalities. Phrases such as “back strain,” “protruding disc,” and “normal wear and tear” are more acceptable to patients than "ruptured disc" or "degenerative arthritis" [43].
History — While it may not be possible to define a precise cause of low back symptoms for most patients, it is important to evaluate three concerns in taking a history:
The psychosocial history helps to estimate prognosis and plan therapy (eg, self-care versus exercise therapy) [44,45]. Potentially useful items are a history of failed previous treatments, substance abuse, and disability compensation. Screening for depression may be helpful.
Underlying systemic diagnosis — Clues that may suggest underlying systemic disease include:
Pain that is not relieved by lying down can be found in patients whose back pain is due to cancer or infection, but is not specific for these conditions. Injection drug use, skin infection, urinary tract infection, or recent fever increase the suspicion of spinal infection. (See "Epidural abscess" and "Vertebral osteomyelitis and discitis".) The presence of ankylosing spondylitis is most commonly diagnosed in men under the age of 40. (See "Diagnosis and differential diagnosis of ankylosing spondylitis in adults".)
Sciatica — Evidence of nerve root irritation typically manifests as sciatica, a sharp or burning pain radiating down the posterior or lateral aspect of the leg, usually to the foot or ankle. Pain radiating below the knee is more likely to represent true radiculopathy than proximal leg pain [46]. Sciatic nerve pain is often associated with numbness or tingling. Sciatica due to disc herniation usually increases with coughing, sneezing, or performance of Valsalva maneuver.
Cauda equina — Bowel or bladder dysfunction may be a symptom of severe compression of the cauda equina, which is a medical emergency. Urinary retention with overflow incontinence is typically present, often with associated saddle anesthesia, bilateral sciatica, and leg weakness. The cauda equina syndrome is most commonly caused by tumor or a massive midline disk herniation. (See "Clinical features and diagnosis of neoplastic epidural spinal cord compression, including cauda equina syndrome".)
Spinal stenosis — Nerve root entrapment in lumbar spinal stenosis is caused by narrowing of the spinal canal (congenital or acquired), nerve root canals, or intervertebral foramina (figure 1). This narrowing is usually caused by bony hypertrophic changes in the facet joints and by thickening of the ligamentum flavum. Disc bulging and spondylolisthesis may contribute. Symptoms of significant lumbar spinal stenosis include back pain, transient tingling in the legs, and ambulation-induced pain localized to the calf and distal lower extremity, resolving with rest. This pain with walking, referred to as "pseudoclaudication" or "neurogenic claudication", is clinically distinguished from vascular claudication by the presence of normal arterial pulses (table 3) [47]. (See "Lumbar spinal stenosis: Pathophysiology, clinical features, and diagnosis" and "Lumbar spinal stenosis: Treatment and prognosis".)
Although pseudoclaudication is a classic finding, it is relatively uncommon. More common symptoms of spinal stenosis are simply persistent back and leg pain that are relieved by sitting or other spine flexion [48]. Among surgical patients with advanced lumbar spinal stenosis documented on myelogram, however, pseudoclaudication was found to be a more frequent symptom [49].
Physical examination — The basic physical examination should include the following components:
Additionally, peripheral pulses should be evaluated in older patients with exercise-induced calf pain to rule out vascular claudication.
Inspection of the patient on physical examination can reveal anatomic abnormalities such as scoliosis (lateral spinal curvature) or kyphosis (spinal curvature with posterior convexity). (See "Overview of hyperkyphosis in older persons".)
Range of motion in flexion and extension does not reliably distinguish among pathologic causes, but can provide a baseline to use as an index of therapeutic response. Limited lumbar flexion is not sensitive or specific for diagnosing ankylosing spondylitis.
Palpation of the back is usually performed to assess vertebral or soft tissue tenderness. Vertebral tenderness is a sensitive, but not specific, finding for spinal infection [50]. However, the finding of soft tissue tenderness is poorly reproducible among observers.
Straight leg raising — The straight leg raise test is useful to help confirm radiculopathy. Straight leg raising is done with the patient supine. The examiner raises the patient's extended leg with the ankle dorsiflexed, being careful that the patient is not actively "helping" in lifting the leg. The test is considered positive when the sciatica is reproduced between 10 and 60 degrees of elevation.
The crossed straight leg raising test refers to elevation of the unaffected leg. The test is positive when lifting the unaffected leg reproduces the sciatica in the affected leg. The seated straight leg test is done while the patient is in the seated position and the lower leg is slowly extended until the leg is flexed at the hip to 90 degrees. If sciatica is present, the pain will be reproduced as the leg is extended.
A positive straight leg test is sensitive, but not specific, for herniated disc [51]. The crossed straight leg test is less sensitive for herniated disks, but 90 percent specific.
Neurologic testing — For patients suspected of having a disc herniation, neurologic testing should focus on the L5 and S1 nerve roots, since 98 percent of clinically important disc herniations occur at L4-5 and L5-S1 (figure 2) [52].
L5 motor nerve root testing evaluates strength of ankle and great toe dorsiflexion. L5 sensory nerve root damage would result in numbness in the medial foot and the web space between the first and second toe.
The S1 nerve root is tested by evaluating ankle reflexes and sensation at the posterior calf and lateral foot. S1 radiculopathy may cause weakness of plantar flexion, but is difficult to detect until quite advanced. One strategy is to have the patient raise up on tip-toe three times in a row, on one foot alone and then the other.
Although ankle reflexes are an important part of S1 nerve root testing, the absence of ankle reflexes becomes increasingly common with age. Among patients without a known pathologic cause of abnormal reflexes, most patients under age 30 have intact ankle reflexes [53]. However, absent reflexes were found in 30 percent of those between ages 61 and 70 and nearly 50 percent of those ages 81 to 90. Unilateral absence of ankle reflexes was found to be uncommon, though, occurring in only 10 percent of those over age 60. Therefore, unilateral absence of an ankle reflex is rare enough to be a clinically useful sign, with a specificity of 89 percent (table 4 and table 5) [54].
Nonorganic signs or Waddell's signs — In patients with chronic pain, psychological distress may amplify low back symptoms, and may be associated with anatomically "inappropriate" physical signs. The most reproducible of these signs are superficial tenderness, distracted straight leg raising (ie, discrepancy between seated and supine straight leg raising tests), and the observation of patient overreaction during the physical examination, also known as Waddell's signs [55]. Other Waddell's signs suggestive of symptom enhancement include nondermatomal distribution of sensory loss, sudden giving way or jerky movements with motor examination, inconsistency in observed spontaneous activity (dressing, getting off table) and formal motor testing, and pain elicited by axial loading (pressing down on top of head, or rotating the body at hips or shoulders). The presence of multiple Waddell's signs may suggest a behavioral component to a patient's pain. However, systematic reviews have not found an association between Waddell's signs and psychological distress, or claims for disability compensation or litigation [56,57].
APPROACH TO IMAGING
Indications — Up to 90 percent of patients with back pain alone (ie, absence of sciatica or systemic symptoms) improve rapidly. Given the favorable prognosis, imaging studies are infrequently needed. This is particularly true for younger women; gonadal radiation from a two view radiograph of the lumbar spine is equivalent to radiation exposure from a chest xray taken daily for more than one year [22]. The American College of Physicians (ACP) advises that diagnostic imaging is indicated for patients with low back pain only if they have severe progressive neurologic deficits or signs or symptoms that suggest a serious underlying condition [58]. They also emphasize the potential harms to patients caused by excessive imaging. Imaging is not necessary during the first 4 to 6 weeks, in the absence of any of the following criteria [5,22,58] (see "Diagnostic testing for low back pain"):
The American College of Radiology has identified 10 "red flags" (table 6), which indicate a more complicated status and may be helpful in identifying patients in whom radiographs, or other imaging studies, would be appropriate [59].
Plain radiographs — If clinical improvement has not occurred after four to six weeks, plain anteroposterior and lateral radiographs of the lumbosacral spine may be useful (two views total). The goal of radiography is to rule out tumor, infection, instability, spondyloarthropathy, and spondylolisthesis. (See "Diagnostic testing for low back pain".)
Joint guidelines from the American College of Physicians and the American Pain Society (2007) explicitly recommend that "Clinicians should not routinely obtain imaging or other diagnostic tests in patients with nonspecific low back pain" and reserve imaging for patients with severe or progressive neurologic deficits or when serious underlying conditions are suspected on the basis of history and physical examination [60].
CT and MRI scanning — Computed tomography (CT) and magnetic resonance imaging (MRI) are more sensitive than plain radiographs for detecting infection and cancer, and can show herniated discs and spinal stenosis. However, MRI or CT findings may be incidental and unrelated to the etiology of low back pain (table 7). (See "Diagnostic testing for low back pain".)
Early or frequent use of scanning is not recommended for most patients. CT or MRI is indicated for progressive neurologic deficits, high suspicion of cancer or infection, and should be considered for those with more than 12 weeks of persistent low back pain. When available, MRI is preferred over CT scan for better visualization of soft tissue and absence of radiation exposure [22]. A more detailed discussion of testing modalities is presented separately. (See "Diagnostic testing for low back pain".)
Relative radiation doses for spine imaging studies are shown in a table (table 8).
INDICATIONS FOR REFERRAL — Referral, usually to a neurosurgeon or orthopedist specializing in back surgery, is indicated when any of the following signs or symptoms are present [61]:
Patients may also be referred to a neurologist or physiatrist if any of the following are present:
APPROACH TO THE PATIENT — A suggested approach to patients presenting with low back pain is shown in an algorithm (algorithm 1). A somewhat more comprehensive algorithm, that addresses diagnosis and treatment for patients with acute or chronic low back pain, has been developed by the American College of Physicians and the American Pain Society [22].
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