eMedicine Specialties > Emergency Medicine > Trauma & Orthopedics

Back Pain, Mechanical

Author: Debra G Perina, MD, Associate Professor, Director of Prehospital Care Division, Department of Emergency Medicine, University of Virginia Health Sciences Center
Contributor Information and Disclosures

Updated: Jul 16, 2009

Introduction

Background

Mechanical low back pain is one of the most common patient complaints expressed to emergency physicians in the United States accounting for more than 6 million cases annually. Approximately two thirds of adults are affected by mechanical low back pain at some point in their lives, making it the second most common complaint in ambulatory medicine and the third most expensive disorder in terms of health care dollars spent surpassed only by cancer and heart disease.¹

Low back pain reportedly occurs at least once in 85% of adults younger than 50 years, and 15-20% of Americans have at least one episode of back pain per year. Of these patients, only 20% can be given a precise pathoanatomic diagnosis. Low back pain affects men and women equally. The onset most frequently occurs in people aged 30-50 years. Low back pain is the most common and most expensive cause of work-related disability in the United States.² Low back pain is not a common complaint in children and, when present, is more likely to have a serious etiology, such as infection or malignancy.³

Pathophysiology

Many causes of mechanical low back pain exist. The most common causes are age-related degenerative disc and facet processes and muscle- or ligament-related injuries. Discussion in this article is limited to musculoskeletal causes. These can be divided into nerve root syndromes, musculoskeletal pain syndromes, and skeletal causes.

Nerve root syndromes

Classic nerve root syndrome is characterized by radicular pain arising from nerve root impingement due to herniated discs. A similar syndrome can also be produced by inflammation and irritation, which may explain why patients whose presentation is consistent with this diagnosis respond to conservative therapies.

Impingement pain tends to be sharp, well localized, and can be associated with paresthesia, whereas irritation pain tends to be dull, poorly localized, and without paresthesia. Impingement is associated with a positive straight leg raising sign (ie, shooting pain down contralateral leg with leg raising), while irritation is not. Neurologic deficits and pain radiation below the knee are rarely seen in irritation alone and are most commonly found with impingement.⁴

The cause of impingement syndrome is most commonly herniated discs, but it may also be caused by spinal stenosis, spinal degeneration, or cauda equina syndrome.

Herniated discs are produced as spinal discs degenerate. After growing thinner, the nucleus pulposus herniates out of the central cavity against a nerve root. Intervertebral discs begin to degenerate by the third decade of life, and herniated discs are found on autopsy in one third of adults older than 20 years. Only 3% of these, however, are symptomatic.⁵ The most common locations for herniation are L4, L5, and S1.⁶

Spinal stenosis occurs when disc spaces decrease as intervertebral discs lose moisture and volume with age. Even minor trauma under these circumstances can cause inflammation or nerve root impingement, which can produce classic sciatica pain without disc rupture. The pain can often be bilateral.⁷

Spinal degeneration is caused by alterations in the hygroscopic quality of the nucleus pulposus. This process progresses to annular degeneration. Coupled with progressive posterior facet disease, this process leads to spinal canal or foraminal encroachment. These retrogressive and proliferative changes in the disc anteriorly and the joints posteriorly produce clinical symptoms and radiographic findings termed 3-joint complex degeneration. Spinal degeneration has 3 distinct stages, as follows:

• Dysfunction with complaints of pain only
• Instability with advanced degeneration, pseudospondylolisthesis, and neurologic abnormalities
• Stabilization with morning stiffness and with prolonged standing or walking, producing radicular pain

Cauda equina syndrome is produced by massive midline extrusion of nuclear material or tumor into the spinal canal, which compresses the caudal sac. The classic presentation is bilateral sciatica, with lower extremity bowel or bladder dysfunction present in 90% of patients. Urinary retention is initially observed and followed by overflow incontinence. Perineal or perianal anesthesia is present in 60-80% of patients.⁸

Musculoskeletal pain syndromes

Musculoskeletal pain syndromes that produce low back pain include myofascial pain syndromes and fibromyalgia.

Myofascial pain is characterized by pain and tenderness over localized areas (trigger points), loss of range of motion in the involved muscle groups, and pain radiating in a characteristic distribution but restricted to a peripheral nerve. Relief of pain is often reported when the involved muscle group is stretched.

Fibromyalgia results in pain and tenderness on palpation of 11 of 18 trigger points, one of which is the low back area, as classified by the American College of Rheumatology. Generalized stiffness, fatigue, and muscle ache are reported.

Other skeletal causes

Other skeletal causes of low back pain include osteomyelitis, sacroiliitis, and malignancy.

Osteomyelitis results from infectious processes involving the bones of the spine, while sacroiliitis results from inflammatory changes in the sacroiliac joints. This pain presents over the sacroiliac joints and radiates to the anterior and posterior thighs. This pain is usually worse at night and is exacerbated by prolonged sitting or standing.

Malignant tumors of the spine can be primary or metastatic. Most primary spinal tumors are found in patients younger than 30 years and usually involve the posterior vertebral elements. Metastatic tumors are found mostly in patients older than 50 years and tend to occur in the anterior aspects of the vertebral body.⁹

Frequency

United States

Mechanical low back pain is one of the most common patient complaints expressed to emergency physicians in the United States accounting for more than 6 million cases annually.

Mortality/Morbidity

• Most etiologies of mechanical low back pain are not life threatening; however, significant morbidity is associated with chronic low back pain syndromes.
• A significant number of patients are unable to return to their normal daily routines or function in a productive work environment secondary to low back pain.²
• Most cases of back pain treated in the emergency department are not true emergencies, with the exception of cauda equina syndrome. Patients who have cauda equina syndrome must undergo surgical decompression as soon as possible or face permanent neurologic damage.

Race

No differences exist in incidence of back pain between racial groups.

Sex

Both male and female populations are affected; however, there is a tendency towards a higher incidence in male patients.

Age

Low back pain is a common complaint in adults of all ages.

Low back pain is not a common complaint in children and, when present, is more likely to have a serious etiology, such as infection or malignancy.

Clinical

History

A thorough history and physical examination is paramount to arrive at a diagnosis, and initially imaging is often unnecessary.⁴

• Patients most often complain of pain in the lumbosacral area.
  • Determine whether pain is exacerbated by movement or by prolonged sitting or standing.
  • Determine the duration of pain.
  • Determine if pain is relieved by lying down.
  • Establish if pain was sudden in onset or gradual over days or months.
  • Determine if pain is worse in the morning or at night.
  • Find out if the patient can identify a precipitating event such as lifting or moving furniture.
• Explore the presence of systemic symptoms such as fever, weight loss, dysuria, cough, and bowel or bladder problems.
• Inquire about current medications that may produce symptomatology.
  • Chronic steroids may predispose to infection or compression fractures.
  • Anticoagulants may result in a bleed or hematoma.
• Any history of new-onset bowel or bladder dysfunction (eg, urinary hesitancy, overflow incontinence) with back pain is suggestive of cauda equina syndrome. This is particularly true if other, new neurologic deficits are also present.

Physical

• Physical examination of a patient with back pain should include range of motion and a thorough neurologic examination, including assessment of peripheral motor function, sensation, and deep tendon reflexes.¹⁰
  • Perform straight leg testing with the patient in a supine position. Record response to raising each leg. An approximation of the test may also be performed with the patient sitting and each leg straightened at the knee. An elevation of the leg to less than 60° is abnormal. The straight leg test result is positive only if the pain radiates to below the knee and not merely in the back or the hamstrings.
  • Perform an abdominal examination to exclude intra-abdominal pathology.
  • Perform a rectal examination on men older than 50 years to assess prostate size and exclude prostatitis. Also perform a rectal examination on any patient who may have cauda equina syndrome to assess rectal tone and perineal sensation. If cauda equina syndrome is suspected, urinary catheterization for a postvoid residual or bedside ultrasonography of the bladder may be helpful to assess for urinary retention.
  • Perform a rectal examination, if necessary, in younger males who are febrile and have urinary complaints.
  • Perform a pelvic examination, if necessary, in females complaining of menstrual abnormalities or vaginal discharge.
• Patients with true herniated discs may not present with any findings other than a positive straight leg raising test. Classic presentation includes numbness in a dermatomal distribution corresponding to the level of disc involved, with findings of motor weakness and reflex loss as described below. Herniated discs have different presentations depending on the location as follows:
  • At L4: Pain along the front of the leg; weak extension of the leg at the knee; sensory loss about the knee; loss of knee-jerk reflex
  • At L5: Pain along the side of the leg; weak dorsiflexion of the foot; sensory loss in the web of the big toe; no reflexes lost
  • At S1: Pain along the back of the leg; weak plantar flexion of the foot; sensory loss along the back of the calf and the lateral aspect of the foot; loss of ankle jerk
  • L5 and S1: These nerve roots are involved in approximately 95% of all disc herniations.
• Spinal stenosis may be present when evidence of degenerative joint disease is present on radiographic studies.
  • Patients with this disease process often complain of progressive pain down the lateral aspect of the leg during ambulation (pseudoclaudication). This pain results from neurologic compression rather than actual arterial insufficiency, which produces true claudication. In cases of spinal stenosis, the straight leg test result is often negative.
  • The stoop test helps distinguish true claudication from pseudoclaudication. Patients with true claudication sit down to rest when pain occurs, while patients with pseudoclaudication attempt to keep walking by stooping or flexing the spine to relieve the stretch on the sciatic nerve.
• Sacroiliitis usually presents with pain over the involved joints and no peripheral neurologic findings.
• Osteomyelitis may be subacute or acute.
  • Clinical findings are nonspecific, and the patient may be afebrile on presentation.
  • Classic presentation includes pain on palpation of the vertebral body, elevated sedimentation rate, and complaints of pain out of proportion to physical findings.
  • Patients particularly at risk for development of osteomyelitis include patients who have undergone recent back surgery, intravenous (IV) drug users, patients with immunosuppression, and those with a history of chronic pelvic inflammatory disease (PID).

Causes

• Mechanical low back pain is a common complaint in patients with functional disorders. In addition, a functional overlay or component of secondary gain may be present in some patients with true organic pathology.¹¹ The degree of psychosocial issues affecting the patient's condition may be assessed by the following:
  • Patient may receive compensation for injury.
  • Patient has pending litigation.
  • Patient dislikes job.
  • Patient has symptoms of depression.
  • Patient caused the accident resulting in back pain.
• Physical clues that help identify patients with significant functional overlay or component of secondary gain include the following:
  • Findings of nonanatomic motor or sensory loss
  • Nonspecific tenderness or generalized tenderness over the entire back
  • Overly dramatic behavior and loss of positive straight leg raising test when patient is distracted
• A particularly useful test is to have patients hold their wrists next to their hips and turn their body from side to side. This test gives the illusion that you are testing spinal rotation, but no actual stress is placed on any muscles or ligaments. Any complaint of pain during this maneuver is strongly suggestive of a functional overlay or component of secondary gain in the presentation.

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