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Outcome Evaluation in Back Pain Patients

Martin H. Pham, Andre M. Jakoi, Neil N. Patel, and Jeffrey C. Wang

■ Introduction

Back pain is among the most frequently encountered problems in medicine; 75 to 85% of the population will experience low back pain (LBP) at some point in life, and 1 to 2% of the United States adult population is disabled because of LBP.^1,2 The yearly prevalence of back pain, alone, is estimated to range from 15 to 20% in the United States and from 25 to 45% in Europe, and these data do not include other pathology involving the spinal column.^1,2 Usually the clinical course is fairly benign, with 90 to 95% of patients recovering within several months. The middle-aged adults are the age subset most commonly afflicted with an even distribution between males and females. However, almost every age population has been noted to be affected. The lower back is the primary site of pain in 85% of those who report suffering from back pain.

Because of this significant prevalence of LBP in the general population, it is important to have useful outcome measures to determine the clinical success of the treatment of this condition. Typical measures of success involve domains of pain intensity, functional disability, and work status. Likewise, identifying the prognostic factors that are associated with good outcomes after the treatment of LBP is important for clinical decision making as well as for understanding this complex multifactorial disease. Identifying the prognostic factors also facilitates selecting the appropriate treatment regimens and for managing expectations of outcome in this patient population.

■ Low Back Pain

Low back pain is the second most common reason (after upper respiratory illness) for all physician visits in the United States. The direct costs associated with these office visits and the indirect costs of time missed from work are considerable. Total incremental direct health care costs due to LBP in the United States were estimated to be $26.3 billion in 1998, and the costs are estimated to increase yearly.³ In addition, indirect costs related to days lost from work are substantial, with 2% of the U.S. work force compensated for back injuries each year. Couple this with the fact that the 5% of the population that receives back pain disability payments accounts for 75% of the costs associated with LBP, and it is clear to see the significant impact that the diagnosis of LBP has on society.⁴

But back pain is an ambiguous condition that leads to myriad diagnoses, a situation that creates enormous problems in patient management. Acute back pain is defined as pain persisting for 1 month or less; fortunately, most patients have self-limited episodes of acute LBP for which they do not seek medical attention.^1,2 For those patients who do seek medical care, cessation of symptomatology and return to work are occur in the first month.5 However, up to one third of patients have reported persistent back pain of at least moderate intensity for more than 1 year after an acute episode, and 20% of those patients have further reported limitations in activity later in life.⁶ These patients would be defined as having chronic back pain, which is pain persisting for longer than 2 months.

There is a multitude of options available for evaluation and management of LBP. However, there is little consensus on which evaluation and treatment are most appropriate.⁷ Numerous studies have shown differences in the use of diagnostic studies and treatment modalities between clinical specialties, but most of the outcomes were the same.^8,9

The patient with back pain presents a challenge to the physician. The patient’s complaint is a symptom, not a diagnosis. A considerable number of anatomic parts of the lumbar spine have the potential to cause pain. In addition, the spectrum of disease processes that may affect paraspinal structures is broad. More than 85% of patients presenting to their primary care physician who have LBP will not have a reliable diagnosis attributed to a specific disease or spinal abnormality.¹⁰ Compounding this problem are the patients who have spinal pain that is associated with a work-related injury or motor vehicle accident. The extent and intensity of symptoms may be exaggerated by nonphysiological factors, thus further muddling the physician’s task in treating patients with back pain, and making it more difficult to identify the entity that is causing the pain and the pathological process producing it.

Unfortunately, in most patients in whom no particular pathological etiology is found, no evidence suggests that labeling with a specific anatomic diagnosis will improve the outcome. Only in a minority of patients who present for initial evaluation does back pain have a specific disorder as its etiology. Malignancy (0.7%), compression fracture (4%), spinal infection (0.01%), ankylosing spondylitis (0.3-5%), spinal stenosis (3%), and herniated intervertebral disk (4%) are the most common diagnosis found on initial evaluation. Although these maladies are regularly seen and manageable pathologies, they make up only a small subset of the diagnoses found and matched with an initial complaint of back pain.^11,12

It is important to have a practical approach to the assessment of the patient with back pain. A focused history and physical examination are always required, and a thorough neurologic examination is also warranted to determine the level of neurologic involvement. Such an approach facilitates the classification of patients into one of three categories: nonspecific LBP, back pain potentially associated with radiculopathy or spinal stenosis, and back pain potentially associated with another specific spinal cause. Diagnostic triage into one of these categories will aid the physician in subsequent decision making. The location of pain, frequency of symptoms, and duration of pain, as well as any previous symptomology, treatment, and responses to treatment, should all be reviewed. Other systems should be explored as well, such as the possibility of back pain on account of pancreatitis, nephrolithiasis, aortic aneurysm, endocarditis, or viral syndromes. All patients should be evaluated for rapidly progressive or severe neurologic deficits including motor deficits, bladder dysfunction, and fecal incontinence.

Clinicians should also inquire about risk factors for malignancy and infection. In a large, prospective study from the primary care setting, a history of cancer, unexplained weight loss, failure to have back pain improvement after 1 month, and age older than 50 years were each associated with a higher likelihood for cancer. The posttest probability of cancer in patients presenting with back pain increases from 0.7% to 9% in patients with a history of malignancy (excluding nonmelanoma skin cancer). Features predicting the presence of vertebral infection include fever, intravenous drug use, and recent infection.¹¹ Clinicians should also consider risk factors for vertebral compression fracture, such as older age, history of osteoporosis, steroid use, and low- or high-energy trauma.

Patients with back and accompanying leg pain and a typical history for radicular pain have a high sensitivity but uncertain specificity for herniated intervertebral disk.13,14 More than 90% of symptomatic lumbar disk herniation occur at the L4-L5 and L5-S1 levels. A focused examination including a neurologic examination that includes the evaluation of strength, reflexes, and sensory distribution should be performed to assess the presence and severity of nerve root dysfunction. A positive result on the straight-leg-raise test has a high sensitivity (91%) but modest specificity (26%) for diagnosing a herniated disk.¹⁵ There is less evidence on the utility of history and examination for identifying lumbar spinal stenosis.¹⁶ The usefulness of pain relieved by sitting for predicting the presence of spinal stenosis ranges from poor to high. Age over 65 years was associated with a positive likelihood ratio of 2.5 and a negative likelihood ratio of 0.33.¹⁷

Psychosocial factors and emotional distress should be taken into account due to their strong predictors of LBP outcomes. In fact, psychosocial factors and emotional distress have a higher prediction factor for back pain outcomes than do either physical examination findings or severity/duration of pain.^18,19 Assessment of psychosocial factors identifies patients who may have delayed recovery in an effort to tailor interventions specifically. These patient-specific interventions may include intensive multidisciplinary rehabilitation, which has been found to be more effective than standard care in patients with acute or subacute LBP and risk factors for chronic back pain disability.²⁰ Psychosocial factors that may ultimately predict poorer LBP outcomes include depression, passive coping strategies, job dissatisfaction, higher disability levels, disputed compensation claims, and somatization.^18,19,21

The pathophysiology of nonradicular LBP is usually indeterminate, and the defining feature of this disorder is its nonspecific etiology. Pain may arise from several sites, including the vertebral column, surrounding muscles, tendons, ligaments, and fascia. Stretching, tearing, or contusion of these tissues can occur after sudden unexpected forces are applied to the spine from either low- or high-energy trauma. Whether muscle spasm is a significant etiology of lumbar spine pain, either as a cause or effect of back injury, has yet to be proven.

The pathophysiology of radicular spine pain and lumbosacral radiculopathy is usually more obvious. Disk herniation through the annulus fibrosis does not in itself produce pain, but compression by the disk on the dural lining around the spinal nerve root sleeve is one explanation for back pain associated with acute disk herniation. This is also likely to contribute to the pain from the spinal nerve compression of arthritic spurs at degenerative facet and uncovertebral joints. Compression can directly stretch nociceptors in dura or nerve root sleeve tissues, but ischemia from compression of vascular structures, inflammation, and secondary edema is also likely to play a role in the causation of pain.

In the initial workup for nonspecific LBP, routine imaging or diagnostic tests are not recommended. There is no evidence that routine plain radiography in patients with nonspecific LBP is associated with a greater improvement in patient outcomes than that with selective imaging.²² This practice of conservative investigation also decreases unnecessary exposure to radiation. This is best illustrated by the fact that a single plain radiograph (two-view) study of the lumbar spine is equivalent to being exposed to a daily chest radiograph for more than 1 year.²³ Routine advanced imaging such as computed tomography (CT) or magnetic resonance imaging (MRI) is also not associated with improved patient outcomes.²⁴ Plain radiography is recommended for the initial evaluation of possible vertebral compression fracture in selected higher-risk patients. Little evidence exists to guide optimal imaging strategies for patients enduring more than 1 to 2 months of back pain, although at that juncture it may be a reasonable initial imaging option. But this is not the case with patients with severe or progressive neurologic deficits. Those patients should receive prompt workup with MRI or CT scans to accompany initial imaging studies.

■ Outcome Measures

The ability to score outcome measures enables the assessment of treatments and of how they improve both functional ability and the subjective experience of pain. Treatment outcomes as measured by patient-reported assessments are not only a reflection of the treatment methods but also of the patient’s perception of their treatment. Many factors are involved in the biopsychosocial aspects of medicine. Although pain levels may be similar among patients, the perceived level of suffering can vary widely.25

Functional outcome measures for LBP are evaluated with regard to LBP-specific disability. For LBP, this disability is determined by pain that typically interferes with the activities of daily living that involve mobility, dressing, sitting, and standing.²⁶ Questionnaires are utilized to determine the severity of these disabilities, and are generally considered to be more reliable than taking a history due to the reproducibility of the same question in exactly the same way to every patient every time.

Commonly used functional outcome measures include the Oswestry Disability Index (ODI) and the Roland-Morris Disability Questionnaire (RDQ). The ODI contains 10 items that reference the activities of daily living that could be disrupted by LBP.²⁷ Each item has six response options ranging from “No problem” to “Not possible” and is scored on a point scale accordingly. The total score is then doubled and expressed as a percentage, with a minimum score of 0 (no disability) and a maximum score of 100 (maximum disability). The RDQ is originally derived from the Sickness Impact Profile and consists of 24 yes/no questions. These focus on physical functions that include walking, bending over, sitting, lying down, dressing, sleeping, self-care, and daily activities. The responses are then summed for a minimum score of 0 (no disability) and a maximum score of 24 (maximum disability). The ODI and RDQ have been found to be valid, reliable, responsive to treatment effects, and applicable in a wide variety of settings.²⁶ Both evaluative measures are interpreted so that the higher the score, the greater the disability.

In addition to functional measures, pain intensity is also a factor that can be measured to assess the success of treatment. Pain intensity is essentially defined as how much a patient is hurt by the LBP. This is quantitatively measured as an estimate of the patient’s perceived severity or magnitude of pain. It is important to keep in mind, however, that despite these quantitative measurements, pain intensity remains a very subjective experience that is determined by the interpretation and assignment of pain by the patient. For the assessment of pain, there is the Numeric Pain Rating Scale (NPRS), Brief Pain Inventory (BPI), Pain Disability Index (PDI), McGill Pain Questionnaire (MPQ), and the Visual Analogue Scale (VAS).²⁸ The VAS consists of a line with each end indicating the extreme levels of pain, range from “No pain” to “The worst pain I have ever experienced.” Points in between correspond to intermediate levels of pain intensity. Patients are asked to select which point along this continuum best represents their pain intensity. Because the VAS continuum line is usually 100 mm long, it has a high number of response categories and can be considered to have as many as 101 response levels. This makes the VAS potentially much more sensitive at detecting differences in pain intensity over time and after treatment regimens. The NPRS is an 11-point scale that instructs patients to rate their pain from 0 to 10. This scale can be expanded to 21 points (rating from 0 to 20) or to 101 points (0 to 100). This pain assessment is easily administered and remains a simple, well-validated, and robust measurement method.²⁶

Although the NPRS and the VAS are often considered the “gold standard” for pain, it is important to note that they have not necessarily been validated specifically for patients with LBP. Nevertheless, pain itself may be the most responsive measure after conservative or surgical treatment for LBP, and therefore it remains a critical measurement.²⁹ Because the NPRS and VAS are so widely used and have been found to reflect the response to treatment, these measures should receive strong consideration for routine use.

The psychosocial aspect of a patient’s well-being is often overlooked on routine questioning and evaluation for clinical LBP. The recent literature has shown, however, that psychological evaluations play a major role in the ability to anticipate and predict outcomes after initiating treatment for LBP. Psychosocial evaluations include the Fear-Avoidance Beliefs Questionnaire (FABQ), Tampa Scale for Kinesiophobia (TSK), and Beck Depression Inventory (BDI). These three evaluative parameters have been validated and found to be reliable within the chronic LBP population.29 Most important with respect to the psychosocial evaluation is whether depression is a domain that would change after treatment of the LBP as opposed to requiring separate treatment itself to affect the overall prognosis of the patient.

Because LBP often results in disability that prevents a continued productive positive contribution to society, the measurement of work status is an important indicator of outcome and treatment effect. Work status can be measured as the duration of sick leave in days, which enables using time to return to work as an outcome measure. Practically, it is known that people who return to work are not as productive as before they developed back pain. Future research will be needed to determine reliable ways to measure productivity at work in different sectors.²⁶

■ Prognostic Factors

Identifying prognostic factors that can influence outcomes after the treatment of LBP is important to manage expectations for both patients and providers. Physicians should be knowledgeable about which factors may portend a poor prognosis in order to provide appropriate counseling and to avoid treatments that entail a higher risk of a less than ideal outcome. It is important to note that there are differences in pain intensity, physical disability, and health-related quality of life across different health care sites, and they also vary by patient age, sex, and race.³⁰ This is important with regard to adjusting patient baseline differences when evaluating factors associated with these outcome measures.

Smoking has been studied extensively in its effect on outcome measures. Former smokers have been found to have somewhat higher levels of physical disability and pain as compared with patients who never smoked.³⁰ Current smokers reported even higher levels of pain and disability. Smoking has been linked to worse back pain outcomes and greater pain, and those who quit smoking were found to have a reduction in pain that is significantly greater than in those who continued to smoke.³¹ Because this is a modifiable risk factor, close attention should be paid to identifying those patients who are current smokers, and appropriate measures taken to counsel these patients about the importance of smoking cessation not just for their overall health, but for the improvement of the LBP that may be a significant factor in their pain and disability.

Age and sex have not been shown to be prognostically associated with decreases in pain or outcome disability at short-term follow-up.³² There is some conflicting evidence that age and sex are associated with outcome disability over longer follow-up times and when reviewed in younger populations, such that women may report persistent greater disability even after treatment intervention.^33–36 Although some studies show statistical significance, the clinical significance of these differences may not be as large as that for the other prognostic factors discussed here.

It has been shown that less educated patients report worse functioning.³⁷ Education may be a marker for other factors such as adaptability to stress, access to health care, occupational factors, and behavioral factors. Additionally, it is possible that less educated patients were at a financial disadvantage and delayed seeking care due to concerns of insurance co-pay costs. The psychosocial stress of low incomes associated with lower education brackets may also affect overall health outcomes. Finally, lower education may be an indication of the cumulative effects of social disadvantage on disease burden that is reflected in worse health-related outcome scores.³⁸

Studies have also found that even after adjusting for geographic location, education, and pain duration, African-Americans were associated with worse baseline physical disability and pain at presentation for back pain-related care as compared with other ethnicities.^39,40 Similar to education status, this could be a result of a variety of other factors, such as lack of access to health care, lower socioeconomic status, and poorer behavioral coping mechanisms.

Patients with leg involvement or spinal stenosis have reported slightly worse physical disability and pain scores on follow-up than did those with otherwise uncomplicated back pain.41,42 This may reflect the compressive etiology associated with radiculopathy and lumbar stenosis as compared with the multifactorial etiology of LBP that may respond robustly to a variety of nonsurgical treatments.

Psychosocial factors and occupational changes may also play a part. The impact of psychosocial factors on the development and perpetuation of chronic pain and disability has been widely demonstrated throughout the literature.^43,44 Psychological conditions such as anxiety, depression, and somatic disorders have been shown to have negative effects on treatment outcomes in both operative and nonoperative cohorts of lower back pain patients.^45–47 Fear-avoidance beliefs as measured by the FABQ have also shown a positive association with outcome disability. To this end, the biopsychosocial model was intended for the successful treatment of LBP. Physicians should consider implementing a psychosocial outcomes measure as part of the routine clinical evaluation for patients presenting with LBP. This would enable appropriate counseling measures as well as the consideration of other psychosocial treatments beyond the realm of just the LBP and associated pain and disability.

Workers’ compensation (WC) patient cohorts have shown typically worse outcomes when compared with those patients without WC claims.^48–50 They show low return to work, high reoperation rates, and high prevalent opioid dependence even at 2 years postoperatively. The conscious or unconscious exaggeration of symptoms likely plays some role when compensation is involved, which subsequently will manifest as adverse effects on self-reported pain, depression, disability, postrehabilitation outcomes, and return to work status.

With regard to outcomes at 12 months, some studies have found statistically significant associations with unemployment, work absence, high functional disability, high pain intensity, anxiety, and poor self-rated health after adjusting for confounding factors.⁵¹ The strongest associations with poor outcome were with unemployment and high pain intensity.

Combining these prognostic risk factors compounded the effect of poor outcome; people with both high pain and high functional disability were seven times more likely to have a poor outcome than people with neither risk factor. Likewise, 78% of patients with poor outcome had both high pain and unemployment at baseline compared with 11% of those with better outcomes. Multivariable regression modeling has shown that unemployment, widespread pain, high level of chronic pain grade, and catastrophizing were significantly associated with disability at 12 months in both acute/subacute and chronic LBP.⁵² Catastrophizing and fear of pain have been found in other studies to be predictive of the development or continuation of pain.^53,54 Another study found a poor prognosis for patients who have taken a previous sick leave for LBP, have high baseline disability levels, or high pain intensity, lower education, or perceive themselves as having a high risk of persistent pain.⁵⁵ Overall, the baseline level of disability was found to be a large predictor of overall outcome and has explained the largest proportion of variance as compared with other prognostic indicators.

■ Chapter Summary

Low back pain is the second most common reason for all physician visits in the United States and presents a challenge to the treating physician. A considerable number of anatomic parts of the lumbar spine have the potential to cause pain. In addition, the spectrum of disease processes that may affect paraspinal structures is broad. Therefore, it is of the utmost importance to utilize outcome measures to provide assessments of treatments and how they improve both functional ability and the subjective experience of pain. In addition, identifying prognostic factors that can influence outcomes after the treatment of LBP is important to manage expectations for both patients and providers. This facilitates performing the appropriate workup and determining the appropriate treatment for the underlying and often multifactorial etiology of the LBP.

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