Musculoskeletal Back Pain

Key Concepts

Most patients presenting to the emergency department (ED) with back pain have uncomplicated musculoskeletal pain that is self-resolving with conservative therapy and does not require imaging.
Indications for emergent imaging include “red flags” such as an acute neurologic deficit, bowel or bladder dysfunction, or saddle anesthesia.
Risk factors for compressive myelopathy include immunocompromised patients with a history of malignancy, injection drug use, fever, chronic steroid or anticoagulant use.
Back pain due to metastatic disease is more common than primary tumors in the spine, and thoracic metastases are more common than lumbar metastases.
Epidural abscess or hematoma, cauda equina syndrome (CES), spinal malignancy with compressive symptoms, and spinal osteomyelitis are all indications for emergent surgical consultation or transfer to a center where surgical spine consultation is available.
Empirical parenteral antibiotics active against staphylococci, streptococci, and gram-negative bacilli should be administered for suspected epidural abscess. Specific antibiotics should be directed against the known pathogen if the culture or Gram stain of the aspirate is positive.
Corticosteroids given as a single dose in the ED (10 mg dexamethasone) or as a 15-day tapering course after discharge (prednisone 60 mg, 40 mg, 20 mg daily for 5 days each) may improve functional ability but does not improve nerve root pain secondary to disc herniation.

Foundations

Background

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.

Epidemiology

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.

Anatomy and Physiology

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.

Pathophysiology

Nonspecific or Uncomplicated Back Pain

In as many as 90% of patients with back pain, no pathologic cause for the symptom can be identified. Research indicates that in many instances of nonspecific pain, factors that increase spinal loading pressure such as obesity and musculoskeletal dysfunction, also reduce spinal stability. Static postures that reduce lateral flexor flexibility and restrict hamstring range of motion contribute to reduced core muscle strength and inadequate support of the spinal column. Weakened core muscles, including those of the anterior abdominal wall, threaten the stability of the remaining muscular and ligamentous spinal support structures, placing patients at risk for activity-related strain. Patients with nonspecific muscular back pain typically have localized pain without radicular symptoms.

Nerve Root Syndromes

Nerve root syndromes comprise a heterogenous group of disease processes that can present with similar clinical symptoms and signs. These syndromes result when there is compression or irritation of a nerve root, causing pain or paresthesias that often radiate into an extremity. Nerve root irritation may occur as the result of muscle tightness or intervertebral disc herniation; however, it can also be caused by pathologies that require urgent diagnosis and management. Therefore, nerve root syndromes should be carefully evaluated to avoid misdiagnoses of etiologies that require emergent intervention. There are multiple possible etiologies for nerve root syndromes. Three major etiologies are discussed in detail here.

With age, intervertebral discs desiccate and degenerate and the nucleus pulposus can herniate through the annulus fibrosis, compressing the nerve root at the neural foramen. Conversely, the annulus fibrosis itself can tear without a true herniation of the nucleus pulposus, also resulting in nerve root irritation. Herniations tend to occur at the L4 to L5 and L5 to S1 levels. This is because most flexion and extension of the spine occurs at the lumbosacral joint and to a lesser degree at L4 to L5, and the supporting PLL is relatively weak at this level of the spine. Although most disc herniations are posterolateral, causing unilateral symptoms, intervertebral discs sometimes herniate centrally, at the level of the cauda equina, causing severe compression of multiple nerve roots, resulting in cauda equina syndrome (CES), as discussed in the following.

Nerve root compression can also be caused by spinal stenosis. Aging causes intervertebral disc space narrowing and deterioration of spine joints. Osteophytes can form at the facet joints, and the ligamentum flavum calcifies over time. These degenerative changes can narrow both the neural foramina and the central canal, causing nerve root compression from osteophytes and increased intrathecal pressure in the narrowed canal. The subsequent pain is often bilateral, unlike that caused by disc herniation. Spinal stenosis also results in leg pain that is typically worse while walking and relieved with forward flexion (thus reducing pressure on the nerve root). This historical information is referred to as the pseudoclaudication sign.

Epidural space occupying lesions can also cause compression to nerve roots or to the cauda equina. Spinal epidural abscesses or hematomas causing nerve compression are true emergencies. Spinal epidural abscesses can result from hematogenous spread of bacteria (often staphylococcal species), in the setting of injection drug use, or from direct inoculation after epidural steroid injection or spinal surgery. Epidural hematomas can result from instrumentation of the epidural space or spinal surgery, although they can also develop spontaneously or following trauma in anticoagulated patients. Regardless of the cause, epidural space lesions causing nerve root compression requires emergent imaging and consultation.

Skeletal Causes of Back Pain

Common bony causes of back pain include fractures, infection, and malignancy.

Fractures may occur in any part of the spine secondary to trauma (see Chapter 35 ). Although a significant amount of force is required to fracture the bones of a normal spine, patients with osteopenia can incur bony fractures with minor trauma. Age-related osteopenia can result in vertebral compression fractures, causing sudden acute back pain with or without trauma. Spontaneous compression fractures occur most commonly within the thoracic or lumbar vertebral bodies. Vertebral fractures may cause radicular symptoms, depending on the location of the injury and impingement on the spinal canal or nerve roots.

Osteomyelitis of the spine is generally caused by hematogenous spread and seeding of the bone by bacteria, resulting in inflammation of the bone and periosteum, and subsequent pain. Injection drug use, spinal surgery, and tuberculosis of the spine (Pott disease), can all cause vertebral osteomyelitis.

Cancer of the vertebral bones is due to primary or metastatic lesions. Primary tumors, such as Ewing sarcoma, multiple myeloma, and osteosarcoma, are less common and usually occur in patients younger than 30 years old, often involving the posterior vertebral elements. Metastatic tumors typically involve the vertebral body and are most common in the thoracic spine, but multiple levels can be affected. Lung and breast cancers make up over 50% of metastatic spinal lesions. Lymphoma, melanoma, cancers of the gastrointestinal (GI) tract, prostate, and kidney, and multiple myeloma may also present as metastatic spinal lesions.

Skeletal back pain can also be caused by nontraumatic congenital or acquired abnormalities of the spine. Spondylolisthesis, or slippage of one vertebral body on another, results from degenerative changes but can also occur after trauma. Retrolisthesis occurs with the posterior slippage of one vertebral body on another. Facet arthropathy is an age-related degenerative cause of skeletal back pain. Inflammatory arthropathies, such as ankylosing spondylitis, rheumatoid and osteoarthritis, can cause similar spinal changes, including pathologic fractures.

Clinical Features

History

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.

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