Your Family Physician

Introduction
Background

Mechanical low back pain (LBP) remains the second most common symptom-related reason for seeing a physician in the United States. Of the US population, 85% will experience an episode of mechanical LBP at some point during their lifetime. Fortunately, the LBP resolves for the vast majority within 2-4 weeks. For individuals younger than 45 years, mechanical LBP represents the most common cause of disability and is generally associated with a work-related injury. For individuals older than 45 years, mechanical LBP is the third most common cause of disability, and a careful history and physical examination are vital to evaluation, treatment, and management.1 (See image below and Image 1.)

Magnetic resonance image of the lumbar spine. Thi...
Magnetic resonance image of the lumbar spine. This image demonstrates a herniated nucleus pulposus at multiple levels.

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Magnetic resonance image of the lumbar spine. Thi...

Magnetic resonance image of the lumbar spine. This image demonstrates a herniated nucleus pulposus at multiple levels.

Numerous treatment guidelines have been written regarding the evaluation, treatment, and management of LBP.2,3 Perhaps the most widely reviewed (and controversial) guideline was published in 1994 by the Agency for Health Care Policy and Research titled "Acute Lower Back Problems in Adults: Clinical Practice Guidelines."4

At the beginning of the 21st century, 750 national and international organizations partnered to create the Bone and Joint Decade (2002-2011).5 This initiative involves patient and professional health care organizations, government agencies, and industries working collaboratively to increase the awareness of bone and joint diseases while increasing the information and research to address this major health care issue. Because 1 in 5 Americans will be age 65 or older by 2030, 65 million people (20% of the total population) will be affected by musculoskeletal impairments, with LBP ranking among the most common problems. Already, total direct and indirect costs for the treatment of LBP are estimated to be $100 billion annually.

The physiatrist represents one type of medical specialist who can evaluate, diagnose, treat, and manage LBP by using medical and nonsurgical procedures and interventions. The physiatrist may have the best functional understanding of all specialists in the treatment and management of mechanical LBP.6,7
Pathophysiology

Causes of mechanical low back pain (LBP) generally are attributed to an acute traumatic event, but they may also include cumulative trauma as an etiology. The severity of an acute traumatic event varies widely, from twisting one's back to being involved in a motor vehicle collision. Mechanical LBP due to cumulative trauma tends to occur more commonly in the workplace.

In a systematic study review, Chen et al investigated whether a sedentary lifestyle (which the authors defined as including sitting for prolonged periods at work and during leisure time) is a risk factor for LBP.8 Examining journal articles published between 1998 and 2006, they identified 8 high-quality reports (6 prospective cohort and 2 case-control studies). While 1 of the cohort studies reported a link between sitting at work and the development of LBP, the other investigations did not find a significant connection between a sedentary lifestyle and LBP. Chen and coauthors concluded that a sedentary lifestyle alone does not lead to LBP.

The pathophysiology of mechanical LBP remains complex and multifaceted. Multiple anatomic structures and elements of the lumber spine (eg, bones, ligaments, tendons, disks, muscle) are all suspected to have a role. (See images below and Images 2, 4.) Many of these components of the lumber spine have sensory innervation that can generate nociceptive signals representing responses to tissue-damaging stimuli. Other causes could be neuropathic (eg, sciatica). Most chronic LBP cases most likely involve mixed nociceptive and neuropathic etiologies.

Diskogram showing examples of an intact disk and ...
Diskogram showing examples of an intact disk and a disrupted disk at the lumbar level.

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Diskogram showing examples of an intact disk and ...

Diskogram showing examples of an intact disk and a disrupted disk at the lumbar level.

Degenerative changes of the lumbar spine, includi...
Degenerative changes of the lumbar spine, including decreased signal intensity and disk bulging at the L-3/4, L-4/5 and L-5/S-1 disks.

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Degenerative changes of the lumbar spine, includi...

Degenerative changes of the lumbar spine, including decreased signal intensity and disk bulging at the L-3/4, L-4/5 and L-5/S-1 disks.

Biomechanically, the movements of the lumbar spine consist of the cumulative motions of the vertebrae, with 80-90% of the lumbar flexion/extension occurring at the L4-L5 and L5-S1 intervertebral disks. The lumbar spine position most at risk for producing LBP is forward flexion (bent forward), rotation (trunk twisted), and attempting to lift a heavy object with out-stretched hands. Axial loading of short duration is resisted by annular collagen fibers in the disk. Axial loading of a longer duration creates pressure to the annulus fibrosis and increased pressure to the endplates. If the annulus and endplate are intact, the loading forces can be adequately resisted. However, compressive muscular forces may combine with the loading forces to increase intradiskal pressure that exceeds the strength of the annular fibers.

Repetitive, compressive loading of the disks in flexion (eg, lifting) puts the disks at risk for an annular tear and internal disk disruption. Likewise, torsional forces on the disks can produce shear forces that may induce annular tears. (see Image below and Image 6.) The contents of the annulus fibrosis (nucleus pulposus) may leak through these tears. Central fibers of the disk are pain free, so early tears may not be painful. Samples of disk material taken at the time of autopsy reveal that the cross-linked profile of pentosidine, a component of the collagen matrix, declines. This may indicate the presence of increased matrix turnover and tissue remodeling.

The various forces placed on the disks of the lum...
The various forces placed on the disks of the lumbar spine that can result in degenerative changes.

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The various forces placed on the disks of the lum...

The various forces placed on the disks of the lumbar spine that can result in degenerative changes.

In lumbar flexion, the highest strains are recorded within the interspinous and supraspinous ligaments, followed by the intracapsular ligaments and the ligamentum flavum. In lumbar extension, the anterior longitudinal ligament experiences the highest strain. Lateral bending produces the highest strains in the ligaments contralateral to the direction of bending. Rotation generates the highest strains in the capsular ligaments.

Research since the late 20th century suggests that chemical causes may play a role in the production of mechanical LBP. Components of the nucleus pulposus, most notably the enzyme phospholipase A2 (PLA2), have been identified in surgically removed herniated disk material. This PLA2 may act directly on neural tissue, or it may orchestrate a complex inflammatory response that manifests as LBP.

Glutamate, a neuroexcitatory transmitter, has been identified in degenerated disk proteoglycan and has been found to diffuse to the dorsal root ganglion (DRG) affecting glutamate receptors. Substance P (pain) is present in afferent neurons, including the DRG, and is released in response to noxious stimuli, such as vibration and mechanical compression of the nerve. Steady, cyclic, or vibratory loading induces laxity and creep in the viscoelastic structures of the spinal elements. This creep does not recover fully in the in vivo cat model, even when rest periods are equal in duration to the loading period.

The concept of a biomechanical degenerative spiral has an appealing quality and is gaining wider acceptance. This concept postulates the breakdown of the annular fibers allows PLA2 and glutamate, and possibly other as-yet unknown compounds, to leak into the epidural space and diffuse to the DRG. The weakened vertebra and disk segment become more susceptible to vibration and physical overload, resulting in compression of the DRG and stimulating release of substance P. Substance P, in turn, stimulates histamine and leukotriene release, leading to an altering of nerve impulse transmission. The neurons become sensitized further to mechanical stimulation, possibly causing ischemia, which attracts polymorphonuclear cells and monocytes to areas that facilitate further disk degeneration and produce more pain.
Frequency
United States

The lifetime prevalence of mechanical low back pain (LBP) in the United States is 60-80%. The prevalence of serious mechanical LBP (persisting >2 wk) is 14%. The prevalence of true sciatica (pain radiating down one or both legs) is approximately 2%.

Of all cases of mechanical LBP, 70% are due to lumbar strain or sprain, 10% are due to age-related degenerative changes in disks and facets, 4% are due to herniated disks, 4% are due to osteoporotic compression fractures, and 3% are due to spinal stenosis. All other causes account for less than 1% of cases. (See images below and Images 1, 3, 5.)

Mechanical LBP is the most common cause of work-related disability in persons younger than 45 years in the United States.

Magnetic resonance image of the lumbar spine. Thi...
Magnetic resonance image of the lumbar spine. This image demonstrates a herniated nucleus pulposus at multiple levels.

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Magnetic resonance image of the lumbar spine. Thi...

Magnetic resonance image of the lumbar spine. This image demonstrates a herniated nucleus pulposus at multiple levels.

Sagittal magnetic resonance image showing loss of...
Sagittal magnetic resonance image showing loss of intervertebral disk height at L5/S1. Herniations of the nucleus pulposus are noted at L4/5 and L5/S1.

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Sagittal magnetic resonance image showing loss of...

Sagittal magnetic resonance image showing loss of intervertebral disk height at L5/S1. Herniations of the nucleus pulposus are noted at L4/5 and L5/S1.

The process of disk degeneration following intern...
The process of disk degeneration following internal disk disruption and herniation.

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The process of disk degeneration following intern...

The process of disk degeneration following internal disk disruption and herniation.

International

Mechanical low back pain (LBP) exists in every culture and country. Estimates by numerous investigators indicate that at some point in their lives, 80% of all human beings experience LBP. Mechanical LBP becomes more prevalent in countries with higher per capita income and where more liberal policies and adequate funds provide for compensation (eg, Germany, Sweden, Belgium).

In Sweden, the level of insurance benefits for disabling LBP is 100%, compared with a range of 0-80% in the United States. In 1987, the percentage of the work force placed on a sick list for diagnoses associated with back pain was 8% in Sweden versus 2% in the United States. In the same year, the average number of days of back-related absence from work per patient per year in Sweden was 40, versus 9 in the United States.
Mortality/Morbidity

While mechanical low back pain is not associated with mortality, morbidity in terms of lost productivity, use of medical services, and cost to society is staggering. Total workers' compensation costs for cases occurring in 1989 in the United States amounted to $11.4 billion, making it the most costly ailment for working-age adults. No evidence has been found to indicate that these costs are declining.
Race

No published information suggests that race is a factor in the prevalence of mechanical low back pain.
Sex

The impact of sex on prevalence of low back pain (LBP) has not been established as well as the roles of other risk factors in LBP (eg, previous LBP, age). A reported 50-90% of women develop symptoms of LBP in the course of pregnancy. Discomfort generally develops in the very early weeks, more commonly in the third trimester. Age, race, occupation, baby's weight, prepregnancy maternal weight, weight gain, number of children, exercise habits, sleeping posture, mattress type, and history of previous LBP have not shown any correlation with the development of LBP symptoms during pregnancy.
Age

Age has been shown to be associated more consistently with mechanical low back pain (LBP) than with sex. The prevalence of LBP during pregnancy appears to increase 5% for every 5 years of patient age. Sciatica (pain that radiates down one or both legs) is usually reported in persons aged 40-59 years. Women aged 60 years or older also report more low back symptoms.
Clinical
History

* Patients generally present with a history of an inciting event that produced immediate low back pain (LBP). The most commonly reported histories include the following:
o Lifting and/or twisting while holding a heavy object (eg, box, child, nursing home resident, a package on a conveyor)
o Operating a machine that vibrates
o Prolonged sitting (eg, long-distance truck driving, police patrolling)8
o Involvement in a motor vehicle collision
o Falls
* Commence the history by asking for the patient's age, hand dominance, and occupation. Also ask about the patient's current work status and last day he or she worked. If the back pain is the result of a work-related injury, ask the name of the employer and inquire how long the patient has worked for this particular employer. Sample questions are as follows:
o When did the current symptoms begin and what were you doing?
o What and where are your symptoms now? (A pain diagram is helpful for localizing the symptoms. The patient can draw on a figure and give the clinician an idea of the nature of the pain as neuropathic or nociceptive.)
o Rate the pain on a scale of 0 (none) to 10 (worst imaginable). This is a global pain rating that takes into account physiological and psychological aspects of the LBP.
o What makes the pain better (eg, sitting, standing, laying, medications, physical therapy)?
o What makes the pain worse (eg, sitting, standing, laying, medications, physical therapy)?
o What affect have these symptoms had on sleep, mood, work, activities of daily living, and/or social functioning?
* Use open-ended questions to ascertain the maximum information about the patient's history. Establishing a rapport with the patient is essential to detect serious conditions, provide insights into the patient's concerns and expectations, and to achieve the optimum positive response to treatment.
* In addition to the history of the present illness, the past medical history should be obtained to rule out infections (eg, septic arthritis), congenital abnormalities (eg, dysplasias, juvenile rheumatoid arthritis), metabolic disorders (eg, Paget disease), or previous traumatic causes (eg, athletic participation, military service).
* The review of systems is helpful for relating the current symptoms to any other body parts or systems. Interruption in bowel or bladder function should be a reminder to consider more serious causes of back pain such as a tumor, infection, or fracture. Review of systems also should include a thorough medical history (including history of cancer, arthritis, infection, systemic disease that could increase susceptibility to infection, nocturnal pain, fever, drug use, depression, and symptoms suggestive of metabolic or metastatic disease). Ask for any history of headaches, peptic ulcer disease, prior cancer, or unexplained weight loss.
* Assess for any history of previous treatments, such as the following:
o Surgery
o Medications: Obtain as complete a listing as possible, including reasons for discontinuation.
o Physical therapy
o Psychiatric or psychological therapy
* Thoroughly screen for anxiety, depression, addiction, somatoform disorders, personality disorders, other prior psychiatric diagnoses, coping styles, and personality traits. Psychosocial factors (eg, depression, hypochondriasis, heavy alcohol consumption, tobacco use, menial work, poor job satisfaction, stressors at home and/or work) may accompany histories involving a work-related injury.
* Assess the patient's vocational history. Look for consistency in the type of work and length of service with each employer since high school or college. Ask how many years the patient has been working for his or her current employer. Some cases have involved patients who have worked less than a week on a new job. Some work-related injuries are reported on a Monday or after a vacation. These are important dates for determining if the LBP was indeed work-related.
* In a work-related LBP case, ask the patient about pending or planned litigation and related expectations.
* Ask the patient what he or she thinks about the cause of the LBP.
* Ask the patient what his or her goals are for the evaluation and treatment.
* If the patient brought imaging study results (eg, plain radiographs, computed tomography [CT] scans, magnetic resonance imaging [MRI] scans), look for imaging evidence of herniated nucleus pulposus, spinal stenosis, or other conditions associated with back pain. (See images below and Images 1, 3.)

Magnetic resonance image of the lumbar spine. Thi...
Magnetic resonance image of the lumbar spine. This image demonstrates a herniated nucleus pulposus at multiple levels.

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Magnetic resonance image of the lumbar spine. Thi...

Magnetic resonance image of the lumbar spine. This image demonstrates a herniated nucleus pulposus at multiple levels.

Sagittal magnetic resonance image showing loss of...
Sagittal magnetic resonance image showing loss of intervertebral disk height at L5/S1. Herniations of the nucleus pulposus are noted at L4/5 and L5/S1.

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Sagittal magnetic resonance image showing loss of...

Sagittal magnetic resonance image showing loss of intervertebral disk height at L5/S1. Herniations of the nucleus pulposus are noted at L4/5 and L5/S1.

Physical

An important part of the physical examination is the general observation of the patient. The patient presents with pain in the low back region and often places his or her whole hand against the skin to indicate a regional pain; however, in some cases the patient may indicate a more precise location.

Realize that much of the physical examination is subjective because a patient-generated response or interpretation to the examiner's questions or maneuvers is required. For example, sensory findings observed during the physical examination and reported symptoms in response to provocative testing are reliant on the patient's response and, hence, represent a somewhat subjective portion of the physical examination. A well-performed and well-documented physical examination, with consistent findings from one visit to the next, can yield important information that may be able to stand up to rigorous scrutiny by any involved third parties (eg, insurance company, attorney, workers' compensation judge). These physical examination findings would need to be put into the context of the patient's symptoms and diagnostic test results.

Equipment often used for the examination includes a stethoscope, goniometer, inclinometer, pinwheel or safety pin, tape measure, and reflex hammer.

* Observe the patient walking into the office or examining room. Observe the patient during the history-gathering portion of the visit for development, nutrition, deformities, and attention to grooming.
* Measure blood pressure, pulse, respirations, temperature, height, and weight.
* Inspect the back for signs of asymmetry, lesions, scars, trauma, or previous surgery.
* Note chest expansion. If it is less than 2.5 cm, this finding can be specific, but not sensitive, for ankylosing spondylitis.
* Take measurements of the calf circumferences (at midcalf). Differences of less than 2 cm are considered normal variation.
* Measure lumbar range of motion (ROM) in forward bending while standing (Schober test).
* The neurologic examination should test 2 muscles and 1 reflex representing each lumbar root to accurately distinguish between focal neuropathy and root problems.
* Measure leg lengths (anterior superior iliac spine to medial malleolus) if side-to-side discrepancy is suspected.
* Using the inclinometer, measure forward, backward, and lateral bending. With the goniometer positioned in a horizontal plane over the axial skeleton (ie, over the head), measure trunk rotation.
* The AMA Guides to the Evaluation of Permanent Impairment (5th edition) include reference tables for all motions, but these figures are not based on empiric data, only on consensus.9 The ROM measurements in the AMA Guides do not correlate with disability and are not consistent within the document itself.
* Palpate the entire spine to identify vertebral tenderness that may be a nonspecific finding of fracture or other cause of low back pain (LBP). Note any asymmetry, misalignment, or step-off between vertebral bodies. Remember also to palpate the sacroiliac joints.
* Test for manual muscle strength in both lower extremities. The Medical Research Council rating is an ordinal scale used for this purpose (0 = absent strength, 1 = trace muscle movement, 2 = poor muscle strength [less than antigravity], 3 = fair muscle strength [antigravity strength through normal arc of motion], 4 = good strength, and 5 = normal strength).
* Table 1. Functional Muscle Testing

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Table
Nerve Root Motor Examination Functional Test
L3 Extend quadriceps Squat down and rise
L4 Dorsiflex ankle Walk on heels
L5 Dorsiflex great toe Walk on heels
S1 Stand on toes* Walk on toes (plantarflex ankle)
Nerve Root Motor Examination Functional Test
L3 Extend quadriceps Squat down and rise
L4 Dorsiflex ankle Walk on heels
L5 Dorsiflex great toe Walk on heels
S1 Stand on toes* Walk on toes (plantarflex ankle)
*When testing the S1 innervated gastrocnemius muscle, the ability to stand on the toes once represents fair (3/5) strength. The patient must stand on his or her toes 5 times in a row to be rated normal (5/5) strength. Note that this approach should allow the physician to detect weakness at a much milder stage than if gastrocnemius strength were assessed only by using the examiner's hand to apply resistance to ankle plantar flexion.
* Test for sensation and reflexes using 0-2 ordinal scale for pinprick sensation (0 = no sensation, 1 = diminished sensation, and 2 = normal sensation), and 0-4 ordinal scale to rate reflexes (0 = no reflex, 1 = hyporeflexic, 2 = normal reflex, 3 = hyperreflexic, and 4 = hyperreflexic with clonus).
* Table 2. Dermatomal Sensory and Reflex Testing

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Table
Nerve Root Pin-Prick Sensation Reflex
L3 Lateral thigh and medial femoral condyle Patellar tendon reflex
L4 Medial leg and medial ankle Patellar tendon reflex
L5 Lateral leg and dorsum of foot Medial hamstring
S1 Sole of foot and lateral ankle Achilles tendon reflex
Nerve Root Pin-Prick Sensation Reflex
L3 Lateral thigh and medial femoral condyle Patellar tendon reflex
L4 Medial leg and medial ankle Patellar tendon reflex
L5 Lateral leg and dorsum of foot Medial hamstring
S1 Sole of foot and lateral ankle Achilles tendon reflex
* Clinical tests for signs of sciatic nerve tension are as follows:
o Supine straight leg raising (SLR) test - Reproduction of pain caused by elevation of the contralateral limb raises the probability of a disk herniation to 98%. Remember that the SLR test result can be negative in persons with spinal stenosis.
o Sitting SLR (knee extension) test (for lower roots) - The patient should sit on the table edge with both hips and knees flexed at 90° and extend the knee slowly. This maneuver stretches the nerve roots as much as a moderate degree of supine SLR. The SLR test result, if positive, reproduces symptoms of sciatica with pain that radiates below the knee.
o The prone SLR test (also called the reverse SLR test or the femoral nerve stretch test) assesses the upper lumbar roots, a less common site of radiculopathy worth remembering.
* Nonphysiologic testing (Waddell signs) should be performed. The presence of 3 or more positive findings out of the 5 types may be clinically significant in terms of psychosocial issues or poor surgical outcome. Isolated positive signs are of limited value.
o Nonorganic tenderness consists of the following:
+ Superficial - Skin tenderness to light pinch over a wide area of lumbar surface
+ Nonanatomic - Deep tenderness over a wide area, often extending cephalad to the thoracic spine or caudad to the sacrum
o Simulation tests give the patient the impression that a particular examination is being conducted, including the following:
+ Axial loading - Vertical loading over the patient's head while he or she is standing, producing LBP
+ Rotation - Back pain when the shoulders and pelvis are rotated passively in the same plane with the feet together
o Distraction tests indicate a positive finding when the patient's attention is distracted.
+ SLR - Observing an improvement of 30-40° when the patient is distracted, compared with formal testing.
+ Flip test - The patient is seated with the legs dangling over the examination table. Instruct the patient to steady himself or herself by holding the edge of the table. When the affected leg is flipped up quickly, the patient falls back and lets go, placing both hands behind him or her on the table.
o Regional disturbances that do not correlate with anatomy include the following:
+ Weakness - Cogwheeling (giving way) of many muscle groups upon manual muscle testing of strength
+ Sensory - Diminished light touch or pinprick sensation in a stocking pattern, rather than a dermatomal pattern, in an individual who is not diabetic
+ Nonanatomic sensory loss
o Overreaction during the examination may be observed in several manifestations (eg, disproportionate verbalization, facial grimacing, muscle tension and tremor, collapsing, sweating). Care must be taken to account for cultural variations.
o In addition, evaluate the patient's function. Observe ROM and flexibility, ability to dress and undress, and ability to rise from a chair or the examination table.

Source : http://emedicine.medscape.com/article/310353-overview