Back pain is one of the most common patient complaints encountered in emergency departments (EDs). Most cases of musculoskeletal back pain are related to physical motion of the vertebrae, intervertebral discs, or musculature of the back; however, a precise pathoanatomic etiology and diagnosis is identified in only 10% of cases. As a result, the symptom of back pain can present the emergency clinician with a challenging diagnostic dilemma. Although most cases of acute or acute-on-chronic back pain are due to uncomplicated musculoskeletal causes, certain types of back pain are true emergencies requiring timely diagnosis and intervention. It is critical to distinguish between the large number of benign presentations of self-limited pain versus less common, high-morbidity causes of back pain that require immediate intervention.

Back pain occurs in children and adults, females and males, with a lifetime prevalence in adults of 60% to 80%. Total direct health care costs and indirect economic expenses associated with back pain are estimated to be in the tens of billions of dollars annually in the United States. Risk factors associated with the development of back pain are numerous and include repetitive lifting and twisting movements, prolonged static (seated) postures, obesity, smoking, and psychosocial factors, such as anxiety and depression.

The spine consists of seven cervical, twelve thoracic, five lumbar, and five fused sacral and coccygeal vertebrae. The vertebrae articulate with each other superiorly and inferiorly at bilateral facet joints, creating four facet joints at each vertebral level. The thoracic vertebral bodies also have bilateral rib facets, which articulate with twelve pairs of ribs. Each vertebral body has bilateral transverse processes and a spinous process. Between the spinous process and the transverse processes are the lamina, and between the transverse processes and the posterior aspect of the vertebral body are the pedicles. Together, the pedicles and lamina form the neural arch, which, along with the posterior aspect of the vertebral body, forms the confines of the vertebral canal that contains the spinal cord and nerve roots. At each level, there are intervertebral (neural) foramina, where the spinal nerves exit.

Between the vertebral bodies are the intervertebral discs, which provide elasticity and stability to the spine. Each disc is comprised of the outer annulus fibrosis, a ring of fibrous tissue, and the collagenous inner nucleus pulposus. The spinal column is connected and stabilized by a network of spinal ligaments including anterior longitudinal ligament (ALL), the posterior longitudinal ligament (PLL), and the ligamentum flavum.

The spinal cord runs superiorly from the foramen magnum, inferiorly to the L1 to L2 interspace, but may extend as low as L3, where it then divides into the cauda equina. The cord is surrounded by three membranes: the tough dura mater, and the delicate arachnoid and pia mater (referred to as the leptomeninges). Cerebrospinal fluid bathes the spinal cord between the arachnoid and pia mater. The epidural space, between the bony vertebral canal and the dura, contains connective tissue padding and the spinal venous plexus. The dural sac ends between S1 and S3. The dura also protects the spinal nerve roots as the nerves exit the spine at each level, just below the correspondingly numbered vertebral body. The movements of the spine are governed by four groups of muscles: posterior extensor muscles of the back; forward flexors of the abdominal wall and the psoas and iliacus; lateral flexors, consisting of the quadratus lumborum, assisted by abdominal wall muscles; and rotators, which are a combination of the extensors and lateral flexors used with unilateral movements.

A thorough history and a directed physical examination is essential in evaluating patients with back pain. Although nonspecific uncomplicated back pain is common, it is critical that emergency clinicians elicit historical information that indicates a higher risk of compressive myelopathy, including history of cancer, unexpected weight loss, trauma, chronic steroid use, anticoagulation, fever, an impaired immune system, injection drug use, or spinal surgery. It is important to assess for “red flag” findings that require emergent evaluation and intervention, such as bowel or bladder dysfunction, saddle anesthesia, and acute neurologic deficits such as bilateral extremity weakness. Important historical data concerning the pain includes: the onset, location, character, severity, duration and radiation of the pain (such as to the abdomen, chest or extremities).

Aggravating and alleviating factors are also important to elicit. Pain that is exacerbated by coughing, sneezing, or bearing down with bowel movements, all of which increase intrathecal pressure, may be associated with a radicular or spinal cause. Pain that is worse with walking or prolonged standing, particularly if relieved by bending forward, suggests spinal stenosis. Pain associated with stiffness that is worse in the mornings and improves through the day suggests a rheumatic etiology. In contrast, pain that is improved with rest is more likely to be muscular or skeletal in nature.

Prior history of back pain, medical or surgical history, and any traumatic events should be documented. Any history of malignancy, or systemic symptoms such as fever, chills, or malaise may indicate metastatic or infectious causes. A history of spinal procedures or surgery should be elicited. Medications such as anticoagulants (associated with epidural hematoma) or chronic corticosteroids (associated with osteopenia) should be reviewed. A family history of autoimmune inflammatory diseases or malignancy may be contributory.

The patient should be asked about any neurologic findings that indicate serious pathology of the spine or nerve roots. These symptoms include sensations of numbness or paresthesias, pain in other locations of the spine, bowel or bladder dysfunction, or weakness in the extremities.

A directed physical examination with the patient undressed is important in evaluating patients with back pain. The examination should include inspection, observation of the patient’s normal movements, palpation, strength and sensory testing, specific maneuvers to assess for serious pathology, and an assessment of deep tendon reflexes. Inspect the overlying skin for erythema, warmth, or areas of swelling, noting any evidence of prior spine surgery or scoliosis. Observe the patient’s general appearance including the presence of jaundice, rashes or contusions, and the patient’s degree of discomfort. Observe the patient’s gait and balance while ambulating. Because core and postural muscle dysfunction contributes to back pain through muscle inflexibility and tightness, range of motion should be tested in several planes. Assess range of motion through flexion and extension at the waist, lateral flexion, and rotation. Palpate the spine to identify areas of maximal tenderness or the presence of muscle spasm.

Perform thorough neurologic testing for strength and sensation. Strength testing of the lower extremities is best done with the patient standing. Instruct the patient to flex both hips and knees, assuming a partial sitting or squatting position. Ask the patient to lift one leg briefly, then the other. Assess heel and toe walking (while holding the examiner’s hands). Performing this activity requires full plantar and dorsiflexion strength, because the entire body weight is carried on a single extremity. If the patient is unable to comply with this approach to strength testing because of pain, this assessment can be performed with the patient reclining, although it is less reliable. Sensory testing is done with the patient reclining or sitting. Testing should include both upper and lower extremities, since some conditions, such as spinal stenosis, may occur at multiple spinal levels, including the cervical spine.

Straight leg and contralateral straight leg raise maneuvers are important in identifying radicular pain. The straight leg raise test is more sensitive but less specific than the contralateral straight leg raise test for the diagnosis of radiculopathy due to disc herniation. The straight leg raise test is performed as follows:

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  Position the patient supine with legs passively extended, without engaging the quadricep muscles. (This can be determined by noting that the patella can move freely side to side.)

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  Raise each leg, flexing at the hip with the knee in extension.

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  A positive test is elicited when pain is reproduced, radiating from the back to a point below the knee of the raised leg at 30 to 40 degrees of elevation. A positive result predicts lumbosacral radiculopathy with a high sensitivity though a relatively low specificity.

Because L5 or S1 discs are implicated in the majority of disc herniations, a negative straight leg raise test is reassuring in ruling out disc pathology. Of note, radiation of pain from the back to the area of the posterior knee or above is a nonspecific finding and of less clinical value.

The contralateral straight leg raise test is performed in an identical manner. A positive test is elicited when pain is reproduced that radiates below the knee of the contralateral leg (the leg that is not being raised). Converse to the standard straight leg raise test, the sensitivity of the contralateral test for disc herniation is low, but the specificity is high. A positive contralateral straight leg raise test strongly suggests disc pathology at the L5 or S1 levels. In summary, if the straight leg raise test is positive, a positive contralateral straight leg raise test can be considered confirmatory of the presence of disc impingement. If the straight leg raise test is negative, but the contralateral straight leg raise is positive, disc herniation or impingement is still highly likely.

Further assessment can provide additional information. Assess the patellar and Achilles deep tendon reflexes, and the plantar reflex. Hyperreflexia, clonus, or a Babinski sign (positive plantar reflex) suggests upper motor neuron pathology, such as a cord impingement. Perineal sensation and anal sphincter tone should be assessed in patients with bilateral symptoms or findings, gait disturbance, severe pain, complaints consistent with saddle anesthesia, or bowel or bladder dysfunction. The cauda equina syndrome is a spinal cord compression below the termination at the conus medullaris (L1–L2) and loss of function of the lumbar plexus. The S3, S4, and S5 dermatomal nerves innervate the “saddle” region and compression causes numbness or tingling to the perineum, anus, and genitalia. Decreased rectal muscle tone may cause loss of bowel function. Bladder dysfunction due to an inability to urinate generally presents as overflow incontinence as a result of urinary retention.

Finally, because pain from abdominal or pelvic pathology often radiates to the back, a thorough abdominal examination, including an assessment of costovertebral angle tenderness and, when indicated, a prostate or gynecologic examination should be performed to exonerate non-musculoskeletal causes of low back pain.

Laboratory testing is generally not indicated for low back pain and when performed is often adjunctive to specific diagnostic imaging. An abnormal white blood cell count (WBC), erythrocyte sedimentation rate (ESR) or C-reactive protein (CRP) may suggest an infectious or inflammatory etiology. For example, while the presence of an elevated ESR is not specific, it should increase the suspicion of spinal epidural abscess, osteomyelitis, or discitis. Marked elevations in the ESR and CRP are often due to infection, but noninfectious disorders such as malignancy, chronic or inflammatory disease, trauma, and tissue ischemia should also be considered. The presence of elevated inflammatory markers should prompt diagnostic imaging.

Coagulation testing is indicated for patients on long-term warfarin; however, the value of coagulation studies has diminished with the increasing prevalence of direct oral anticoagulant (DOAC) use. If coagulation studies are abnormal in the setting of low back pain, epidural or retroperitoneal bleeding should be explored. Urinalysis, and urine pregnancy testing in female patients, can be useful in establishing non-musculoskeletal causes of back pain, such as nephrolithiasis, pyelonephritis or pelvic etiologies.