Lisa J. Reeves, M.D. and Alex Montero, M.D., M.P.H.


"Doctor, my back hurts"

Low back pain is among the most common complaints reported to the outpatient generalist, yet it often evokes a mixed reaction. As a pain syndrome with no objective anatomic cause in more than 60 percent of patients, it frustrates many providers. This chapter reviews common causes of low back pain and provides a syndromic approach to the problem, with the goal of helping the patient to regain function in a way that brings satisfaction to both patient and physician.


The lifetime prevalence of low back pain (LBP) in most industrialized countries is between 60 and 80 percent., Fifteen percent of the U.S. population has an episode of LBP annually, with the highest prevalence among persons aged 45 to 64. Fourteen percent of American adults will have an episode of low back pain that lasts more than two weeks at least once in their lifetimes, and five percent will have chronic low back pain. In other words, more than 30 million American adults at any one time have low back pain lasting for more than two weeks and there are more than 10.5 million chronic sufferers. Given these numbers, it is no wonder that U.S. expenditures for medical care of low back pain are huge, exceeding $24 billion in 1990 direct costs alone. Total costs come closer to $100 billion when estimates of lost productivity and workers’ compensation claims are included.5

In the average primary care practice, the vast majority of patients with low back pain have lumbosacral strain or osteoarthritis. Compression fracture accounts for four percent.8 Only one to two percent have associated disc herniation with radiculopathy ("sciatica"), and another three percent have clinically significant spondylolisthesis., A very small percent suffer from a systemic or nonmechanical back problem, such as primary or metastatic malignancy (0.7 percent), ankylosing spondylitis (0.3 percent), or spinal infection (0.1 percent)., Table 1 provides a comprehensive differential diagnosis of low back pain presenting in primary care:


TABLE 1: Differential Diagnosis of Low Back Pain*

Mechanical Low Back Pain or Leg Pain (97%)†

Nonmechanical Spinal Conditions (About 1%)

Visceral Disease (2%)


Lumbar strain, sprain (70%)§

Neoplasia (0.7%)

Disease of pelvic organs

Degenerative processes of disks

Multiple myeloma


and facets, age-related (10%)

Metastatic carcinoma


Herniated disk

Lymphoma and leukemia

Chronic pelvic inflammatory

Spinal Stenosis (3%)

Spinal cord tumors


Compression fracture ** (4%)

Retroperitoneal tumors

Renal disease

Spondylolisthesis (2%)

Primary vertebral tumors


Traumatic fracture (<1%)

Infection (0.01%)


Congenital disease (<1%)


Perinephric abscess

Severe kyphosis

Septic diskitis

Aortic aneurysm

Severe scoliosis

Paraspinous abscess

Gastrointestinal disease

Transitional vertebrae

Epidural abscess


Spondyolysis ¶



Internal disk disruption or

Inflammatory arthritis

Penetrating Ulcer

Diskogenic low back pain║

(often HLA-B27) (0.3%)


Ankylosing spondylitis


Psoriatic spondylitis


Reiter’s syndrome


Inflammatory bowel disease


Scheuermann’s disease




Paget’s disease of bone


* Table adapted from Deyo.36 Percentages are estimates of these conditions among all adult patients with low back pain in primary care. Diagnoses in italics are often accompanied by neurogenic leg pain.

†"Mechanical" designates an anatomical or functional abnormality without an underlying malignant, neoplastic, or inflammatory disease.

§"Strain" and "sprain" are nonspecific terms with no pathoanatomical confirmation. "Idiopathic low back pain" may be a preferable term.

¶ Spondylosis: degenerative disc narrowing and vertebral osteophyte formation (as common among asymptomatic persons with and without back pain; its role in causing low back pain remains ambiguous). Spondylolisthesis: anterior displacement of a vertebra upon the one beneath it, often a result of DJD.

║Internal disk disruption is diagnosed by provocative discography which is often positive in asymptomatic patients). Thus, the clinical import and management of this condition remains unclear.

**Compression fractures can be classified as either mechanical or nonmechanical at they usually occur in the setting of metabolic bone disease (osteoporosis).

Evaluation of Acute Low Back Pain

Low back pain syndromes should first be categorized by duration of symptoms. Acute low back pain is defined by the Agency for Health Care Policy and Research (AHCPR)3 as activity intolerance due to LBP or back-related symptoms that lasts less than three months. Other authors have divided the first 12 weeks of back pain into "acute" (less than four weeks) and "subacute" (4-12 weeks).2 This chapter will focus on the evaluation and treatment of acute low back pain, discussing the management of subacute and chronic LBP more briefly. A fruitful approach is to triage as follows: is the pain emergent? Is it nonmechanical? Is it mechanical? Answering these questions will permit the provider to develop a rational diagnostic strategy.

Emergent Low Back Pain

The first question the provider must answer is whether or not the back pain is an emergency. Life-threatening or neurologic emergencies require immediate evaluation and subspecialty referral. Examples include dissecting aortic aneurysm, spinal cord compression and cauda equina compression syndrome. As noted, these are extremely rare causes of low back pain, but ones that should never be missed. Alarm features include new, severe, or progressive lower extremity weakness; new bowel or bladder sphincter disturbances (often manifested by incontinence); and dermatomal sensory abnormalities outside of the L4-S1 distribution such as "saddle" anesthesia. Such patients require immediate radiologic evaluation and referral.

Nonmechanical Back Pain

Having excluded emergent causes of back pain, the next step is to decide whether a non-mechanical ("medical" or "systemic") etiology – such as infection, malignancy, bone disease, or inflammatory arthritis – is to blame. A careful history is essential, and should include Borenstein’s five symptom-complex questions:1

  1. Has the low back pain been accompanied by fever or weight loss?
  2. The three cancers most likely to metastasize to the spine are breast, lung and prostate. In patients with a history of neoplasm or strong evidence to suggest neoplasm, new back pain has an 98 percent specificity for malignancy.3 All such patients should proceed to immediate radiologic evaluation. While malignancy is the most common systemic disease affecting the spine, it accounts for less than one percent of low back pain.8 A study of nearly 2000 patients with back pain found no cancer in patients under the age of 50 without a history of prior malignancy, unexplained weight loss, or failure to respond to conservative therapy (combined sensitivity ~ 100 percent).11

    Fever raises the possibility of spinal infection, but must be interpreted with care. Two percent of patients with mechanical (i.e. non-infectious) back pain will have a fever, from unrelated causes, including benign viral syndromes.11 As noted, only 0.1 percent of patients with low back pain will have a spinal infection. Almost all bacterial infections of the spine are due to hematogenous spread from another site. Thus, only patients with known bacterial infection, or a clear risk factor for one, should undergo evaluation for a spinal infection. Urinary tract infections (and thus indwelling catheters), bacterial skin infections (and thus indwelling central lines), and injection drug use are the most commonly identified causes of spinal infections, and are found in 40 percent of patients. Fever in the setting of bacterial infection and new back pain is 98 percent sensitive for spinal infections, although specificity is variable.,

  3. Is the pain worse with recumbency or at night (such that the patient must sit in a chair to sleep)?
  4. Pain on recumbency may be the result of spine or spinal cord tumors as the position stretches nerves over an expanding mass. This symptom is not specific for tumor and, as stated, tumors are a rare cause of LBP. For example, spinal stenosis is a much more common condition that also produces pain on recumbency.

  5. Is there morning stiffness that lasts for hours?

This question is intended to exclude spondyloarthropathy. A classic article by Calin et al. describes a five-question screening test for ankylosing spondylitis (AS):

Although affirmative answers to four of five questions is sensitive and specific, AS is rare, making the positive predictive value only four percent8.

  1. Is there pain directly over the bone itself?
  2. Pain directly over the spine is highly suggestive of osteoporotic compression fracture in the proper clinical context. In patients who are older than 70, who have a history of long-term corticosteroid use, or who have known osteoporosis, point tenderness over the bone is highly specific (96-99 percent) for compression fracture and an x-ray should be obtained.8 In younger patients, particularly those who are active and healthy, the pain is much more likely to be caused by paraspinal muscle strain.

  3. Is the pain periodic or cyclical?

An affirmative answer to this question should prompt the physician to consider causes of referred pain from the gastrointestinal or genitourinary tracts, such as endometriosis or nephrolithiasis.

TABLE 2: Screening questions for nonmechanical lower back pain

Has the pain been accompanied by unexplained weight loss?

Does the patient have a history of cancer?

Has the pain been accompanied by fever?

Does the patient have an indwelling catheter or central line?

Does the patient use injection drugs?

Is there morning stiffness that lasts for hours?

Is there pain directly over the bone itself?

Does the patient use chronic steroids?

Does the patient have osteoporosis?

Is the pain periodic or cyclical?

Mechanical Back Pain

Once it is clear that the back pain is not life-threatening, does not require surgical evaluation, and is not part of a systemic disease process, the provider may comfortably assume that the low back pain is a function of mechanical injury. Borenstein defines mechanical low back pain as "pain secondary to overuse of a normal anatomic structure (e.g., muscle strain) or deformity of an anatomic structure (e.g., herniated nucleus pulposus)."

All acute LBP due to mechanical injury has the same short-term prognosis, unless severe neurologic deficit is present. Thus, in the absence of severe or progressive neurologic symptoms or signs, all such syndromes are treated in the same way (see Therapy, below). The purpose of identifying the etiology of LBP is to guide long-term management and patient counseling.

Most mechanical back pain results from either lumbosacral strain or osteoarthritis. Lumbosacral strain is the most common cause of LBP;17 persons 20 and 40 years of age are at the highest risk. The exact location of the injury is often unknown, but is presumed to be due to muscular, ligamentous or fascial strain, caused either by acute traumatic injury or by continuous mechanical stress. Predisposing features include obesity, poor lifting technique, abnormal pelvic tilt, and leg length disparity. Point tenderness over a muscle or muscle spasm on exam will help make the diagnosis of a muscle strain.

Osteoarthritis is the next most common cause of low back pain. OA causes at least three different back pain syndromes. Patients may complain of localized LBP, suggestive of injury to the apophyseal (facet) joints due to chronic hyperextension trauma (stretching and tearing of the ligamentous capsules of the joints). Patients may also complain of localized pain in addition to referred pain radiating to the buttocks or posterior thigh. The referred pain is a function of inflammation of the surrounding tissues. Lastly, patients may complain of localized back pain with lower leg pain. This syndrome, commonly called "sciatica" by laypersons, often occurs because of degeneration of the intervertebral discs, or the development of osteophytes that impinge on the nerve root. The evaluation and management of this syndrome is discussed below.

The patient’s age will help to direct your differential diagnosis. Younger adults are much more likely to have lumbosacral strain, middle-aged patients are prone to disc herniation, and older patients commonly have osteoarthritis, spinal stenosis or fracture. With these entities in mind, many practitioners choose to subdivide mechanical low back pain into four categories, based on the location and radiation of pain:

TABLE 3: The differential diagnosis of "sciatica:

The most common cause of radicular pain is disc herniation of the nucleus pulposis, with resultant nerve root impingement.10 Other causes include foraminal (spinal) stenosis, lateral stenosis, piriformis syndrome and external impingement of the nerve root by tumor or abscess.

In spinal stenosis, the foraminal canal is narrowed due to increased bone formation, impinging both on nerves and on their blood supply. Patients experience back pain and radicular leg symptoms, often associated with extension. Walking - or in advanced cases merely standing - exacerbates the condition, a fact which helps to differentiate this neurogenic claudication from vascular claudication. Sitting or flexion of the back often relieves the pain. Systemic pain medication and epidural injection are often unsuccessful, and patients may eventually require decompression surgery in order to regain some mobility. Surgery is often considered a last resort, since it is highly invasive and success rates are limited.

Piriformis syndrome is the result of trauma to the piriformis muscle, located in the sciatic notch. Inflammation and spasm of the muscle may impinge on the sciatic nerve. This is not uncommon, and may be diagnosed in several ways: 1) piriformis muscle tenderness during rectal exam, 2) a positive Frieberg’s sign (pain with internal rotation of the straight hip), or 3) a positive Pace’s sign (pain with abduction of the flexed knee against resistance).2

A variety of other nerve and musculoskeletal derangements cause nonradicular pain that mimics radicular pain, including osteoarthritis of the hips, trochanteric bursitis, meralgia paresthetica, diabetic amyotrophy, and vascular claudication. Trochanteric bursitis deserves special mention, because of its high prevalence. This syndrome may be diagnosed by reproducing the pain on palpation over the greater trochanter. Other clues include ipsilateral leg pain, iliotibial band tenderness, pain with crossed legs, and pain while lying on the affected side.2 Meralgia paresthetica is a syndrome in which patients complain of numbness or tingling in the anterior lateral aspect of the thigh. This is due to compression of the lateral cutaneous femoral nerve, often due to large abdominal girth or a tight belt compressing the nerve.


Evaluation of Back Pain Syndromes with Lower Extremity Symptoms


It is essential to evaluate the quality and distribution of lower extremity symptoms. Sensory abnormalities are common and a useful aid for localizing the problem. More than 95 percent of disc herniations occur at the L4-L5 or L5-S1 levels; patient symptoms usually involve the lower leg. Many people describe either a sharp burning or lancinating pain, or a tingling or numb sensation in the distribution of a nerve root. This type of pain is called "radicular" pain in the medical literature and "sciatica" in the vernacular. (The OED cites a 1450 use of the word "sytyca"; Shakespeare uses "ciatica" in Measure for Measure and "sciatica" in Timon of Athens). The symptom is most commonly caused by herniation of the nucleus pulposus. Complaints of radicular pain are 95 percent sensitive for nerve root compression.8 In the absence of leg pain or paresthesia, the likelihood of a clinically important lumbar disc herniation – or any nerve root compression – is very low (less than 0.1 percent). Patients may also complain that sitting worsens the pain, a symptom complex that occurs because flexion of the lumbar spine further irritates the nerve root. This mechanical process is the basis of the straight leg raising (SLR) test, described in Table 4. While sensory symptoms are common, and should not be alarming to the physician, motor weakness and/or change in bowel or bladder function are "red flags," indicating the possibility of a neurologic emergency.

Physical examination:

A positive straight leg raising (SLR) test is one in which the radicular leg pain is reproduced in the leg that is raised between 30 and 60 degrees. No tension is placed on the nerve root until the hip is flexed approximately 30 degrees, and pain at less than 30 degrees is not consistent with nerve root compression. Low back pain or a "stretching sensation" in the calf does not count as a positive test. The SLR test is 80 percent sensitive for nerve root impingement, but is not specific for disc herniation. A positive "crossed leg" SLR test is one in which the radicular pain is reproduced in the resting leg. This variant is not more sensitive, but it 90 percent specific for disc herniation.


TABLE 4: How to perform the straight leg raising (SLR) test

  • Have the patient lie supine on the examining table
  • Cup the heel of the painful leg in one hand and keep the knee fully extended with the other hand
  • Raise the leg slowly from the table

The crossed SLR test is performed in the same way, but on the leg without pain


A careful neurologic exam is required, but can be focussed on the L4-S1 distribution. Pinprick can be used to assess sensory deficits over the leg and foot, as illustrated in Figure 1. Testing sensation over the medial (L4), dorsal (L5) and lateral (S1) aspects of the foot is an efficient way to evaluate these dermatomes. Disc herniations with nerve root impingement case radicular pain and paresthesias, but can also produce weakness in the L5 or S1 distribution. Motor and reflex abnormalities are less common and, as noted, may indicate a more serious problem that requires immediate evaluation by the neurologist or surgeon. The most obvious and reproducible neurologic impairments are weakness of the ankle and great toe dorsiflexion (L5). These should be evaluated by having the patient dorsiflex the foot or the great toe against the examiner’s resistance while supine. An alternative choice is to have the patient stand or walk on his/her heels, although this more complicated task may be less specific.


Imaging studies

In younger patients (age < 50) with uncomplicated (mechanical) LBP, imaging is not necessary in the first four to six weeks of symptoms. However, prompt plain radiography is recommended for patients with fever, unexplained weight loss, history or cancer, neurologic deficits, alcohol or injection-drug abuse, chronic steroid use, or age over 50. Plain radiography is recommended for all patients who fail to improve in four to six weeks as most mechanical etiologies will have resolved improved by this time.36

CT and MRI are more sensitive than plain radiography for detection of early spinal infections and cancers. In addition, these modalities can detect disc herniations and spinal stenosis. However, they are not indicated in the initial evaluation of patients with mechanical back pain. Aside from cost considerations, the low positive predictive value of these modalities is problematic. For example, 35 percent of asymptomatic patients will have an abnormality on lumbosacral CT scan, 31 percent on MRI, and 25 percent on myelogram.,, Hence, when used inappropriately these studies will only confuse the diagnostic picture and result in overdiagnosis, patient anxiety, and further unnecessary diagnostic or therapeutic interventions. CT and MRI should be obtained only when there is a strong clinical suspicion of infection, cancer, or persistent neurologic deficit. CT and MRI should also be obtained preoperatively in patients who have meet criteria for surgery.36

TABLE 5: Criteria for prompt plain radiography in the evaluation of LBP

Any of the following:

  • Fever, unexplained weight loss, or hx of cancer
  • Hx of trauma
  • Presence of neurologic deficits
  • History of corticosteroid use or known osteoporosis
  • History of injection drug use
  • Age > 50
  • The patient is seeking compensation for back pain.

Adapted from sources , and 36.

Treatment of Mechanical Low Back Injury

Ninety-five percent of people with acute, mechanical low back pain will have complete recovery within two months. Conservative therapy is, therefore, the preferred course of action. The goal of treatment is to manage pain and to help patients regain their usual function as quickly as possible. Educating patients as to the likely time course of symptoms will help create appropriate patient expectations for recovery. The key is to note improvement over time.

Conservative Therapy 1,3,36

  1. Controlled or limited activity for a short period (one to two days) followed by progressive mobilization and low stress exercise (walking, swimming, or bicycling). After two weeks of activity, conditioning exercises for the trunk may be added.
  2. Bed rest is indicated only for severe cases, and then only for one to two days. Deyo analyzed outcomes of 203 people randomly assigned to two or seven days of bed rest for acute back pain. Although clinical outcomes were similar, patients on prolonged bed rest missed 45 percent more work days. The authors hypothesized that prolonged bed rest promoted disability via deconditioning or re-enforced sick-role behavior. Similar randomized trials confirm that bed rest is an ineffective intervention, and that sick leave is rarely required.
  3. NSAIDS (traditional or Cox-2 inhibitors) or acetominophen are mainstays of analgesic therapy. Tramadol is appropriate for patients intolerant or failing the analgesics mentioned above.
  4. Heat treatment – continuous low-level heat wrap therapy – was shown in one trial to be more effective than either ibuprofen or acetominophen in patients with acute LBP.
  5. Muscle relaxants (in addition to NSAID therapy) have been found to be efficacious only in the setting of muscle spasm. They are commonly sedating (especially in the elderly) and their use should be judicious.
  6. Opioids should be avoided or used sparingly as there is no proof of their superiority to NSAIDS and their side effect profile is significant.
  7. Back injections (facet joint or epidural) are rarely indicated. They may be provided by an orthopedist once first-line therapies have failed. There are no long-term benefits to this approach, but it can offer rapid, if transient, relief.
  8. Physical modalities (cryotherapy or thermotherapy), traction, and transcutaneous nerve stimulation (TENS) have neither long-term benefit or harm.1,27, However, they may have limited short-term positive effects. Alternative therapies such as spinal manipulation and massage therapy have been shown to have some efficacy in subacute/chronic LBP, whereas acupuncture has been shown to be ineffective.37,
  9. Physical therapy is not indicated in acute low back pain. Similarly, back exercises are ineffective in acute LBP but helpful in preventing recurrences or in treatment of chronic LBP.

Surgical Therapy

Most patients with mechanical low back pain will not require surgery. However, a subset of patients with sciatica, spinal stenosis, and spondylolisthesis may ultimately benefit from surgery. Surgery is most effective for disc herniation with improved outcomes at four years. Long term outcomes are equivocal with no difference at ten years. Surgery for spinal stenosis is less successful with 10% undergoing reoperation at four years36.


Table 6: Indications for Surgical Referral Among Patients with Low Back Pain*

Sciatica and Probable Herniated Disks

The cauda equine syndrome (surgical emergency)

Progressive or severe neurologic deficit

Persistent neuromotor deficit after 4-6 weeks of nonoperative therapy

Persistent sciatica (not low back pain alone) for 4-6 weeks, with consistent clinical and neurologic findings

(in this circumstance, and for persistent neuromotor deficit, surgery is elective, and patients should be

involved in decision making)


Spinal Stenosis

Progressive or severe neurologic deficit, as for herniated disks

Back and leg pain that is persistent and disabling, improves with spine flexion, and is associated with spinal

stenosis on imaging tests; surgery is elective, and patients should be involved in decision making



Progressive or severe neurologic deficit, as for herniated disks

Spinal stenosis with referral indications as above

Severe back pain or sciatica with sever functional impairment that persists for a year or longer


*Adapted from 36

Subacute and Chronic Back Pain

As noted, only five percent of patients fail conservative therapy. However, since the overall number of people who experience low back pain is so large, this leaves millions of Americans with chronic low back pain. The primary care provider must be prepared. If symptoms do not improve after four to six weeks, the situation must be re-evaluated. Manzanec2 offers the following key questions: Is the original diagnosis correct? Was the initial therapy appropriate? Is there a need for physical reconditioning?

These questions can be answered by reviewing the history and physical exam. Some LBP diagnoses are elusive (e.g., trochanteric bursitis or piriformis syndrome) and relief may not occur until very specific therapies are offered – such as steroid injection at the site of pain.18,19 Other injury, particularly muscle strain, may re-occur with repeated injury, or self propagate in a "domino" effect, prolonging the pain syndrome as new muscles are injured in an attempt to compensate for the original injury. Certain injuries, most notably disc herniation or spondylolisthesis, can be slow to heal in the presence of deconditioning or weight gain. Finally, some mechanical pain syndromes – such as spinal stenosis or osteoarthritis – simply progress over time and fail medical treatment.

Treatment of chronic LBP can be vexing. However, metanalysis has shown that intensive ( >100 hours of therapy), multidisciplinary, biopsychosocial rehabilitation (all included physical therapy) is superior to usual care for chronic low back pain. Intensive exercise programs have also been proven effective. Hence physical therapy was is a mainstay of therapy of chronic LBP. With respect to medical therapy, antidepressants have been shown to be efficacious in one third of patients with chronic LBP who also have depression. 36,38

Psychosocial conditions, such as anxiety, depression, and substance abuse are common among patients with chronic low back pain, and can potentiate symptoms. One prospective study used structured psychiatric interviews to demonstrate an anxiety disorder, depression or substance abuse in 59 percent of patients with chronic low back pain; the psychiatric condition antedated the back symptoms in more than 50 percent of these patients. Identifying a psychiatric illness may suggest additional treatment modalities; it is important to remember that the presence of these diagnoses does not lessen the significance of chronic pain nor the disability it can cause.

If the diagnosis of an ongoing pain syndrome is unclear or does not seem physiologic, physicians should also evaluate for malingering. Certain psychosocial barriers, such as job dissatisfaction or economic incentive may play a role in the delayed recovery process. Waddell et al. suggest a quick five-step evaluation for "non-organic" pain, which is more likely with:

  1. inappropriate tenderness that is superficial, widespread or non-anatomic
  2. overreaction during physical exam (which should be interpreted with caution and consideration of cultural variation)
  3. positive "distraction" sign, inconsistent performance between SLR testing in seated and supine positions
  4. pain on simulated axial loading (pressing on the top of the head) or simulated spine rotation (hold the patient’s arms to his/her sides and rotate hips and shoulders together)
  5. Regional disturbance in strength and sensation that does not correspond with nerve root innervation.

Tenderness that seems to wander or to change position during the actual physical exam is also a "red flag." The sensitivity and specificity of these maneuvers has not been demonstrated, although the first three are felt to be the most reproducible. If three of the five are positive, this suggests psychological distress.

It is critical to evaluate the source of delayed recovery promptly. There is a 50 percent probability of returning to work after six months of disability, a 25 percent chance at one year, and close to zero percent after two years.


The evaluation of low back pain is challenging. While the inability to identify a specific cause of pain may be frustrating, the favorable prognosis of most acute back pain should make the care of this syndrome more rewarding. The role of the physician in the initial management of low back pain is to identify the rare patient who has a serious (usually non-mechanical) source of pain, to offer pain management and counseling, and to facilitate recovery and maintenance of previous function. For patients who do not respond to conservative therapy, the physician must re-evaluate the diagnosis and treatment, with a careful eye to the role of non-organic issues.