Are measures of function and disability important in low back care?

Key Words: Backache; Disability evaluation; Tests and measurements, functional.

Low back syndrome (LBS) and the resulting disablement cost industrialized societies billions of dollars in direct and indirect health care,[1-3] and the increased incidence of LBS from the 1960s through the 1980s has been characterized as epidemic.[4] For the purposes of this article, low back syndrome is defined as pain, paresthesia, and related symptoms that are believed to emanate from the lumbar spine (this definition includes low back pain and sciatica). Patients with

LBS account for the majority of visits to orthopedists, neurosurgeons, and occupational medicine physicians.[5,6] With surgery less and less of an option, the vast majority of patients with LBS are eventually directed toward conservative management, and evidence suggests that such patients comprise a high percentage of the patients seen by physical therapists in typical outpatient facilities.[7,8]

Characterizing disablement associated with LBS necessitates that the term "disability" be used in a consistent and defined manner. In the context of this special issue, disability is defined as a restriction in a person's ability to perform socially defined roles. Most well-established LBS disability ratings, including publications from the American Medical Association,[9] the American Academy of Orthopedic Surgeons,[10] and the US Social Security Administration,[11] rely almost entirely on diagnoses based on pathology in determining disability ratings. This is in spite of the consensus that (1) the vast majority of patients with LBS are without a diagnosis based on pathology[12] and (2), even if present, diagnoses based on pathology are only a part of the disablement picture.[13] Without a diagnosis to guide treatment, many clinicians encourage documentation of disablement from the patient's perspective, relying on patients' perceptions of their limitations or diminished capacities for everyday activities.

Clinical tools exist for characterizing physical impairments, functional limitations, and disability in patients with LBS. Some of these tools administered as part of clinical examinations require active participation of health professionals, whereas others are self-administered (eg, patient self-reports). In this article, measures of impairment, functional limitations, and disabilities specific to patients with LBS are described, My approach will be first to characterize disablement due to LBS within the framework of the pathology-driven Nagi scheme and to offer an alternative model. The physical therapist's role in documenting the physical impairments and functional limitations in patients with LBS will then be discussed. Next, specific self-reports of functional limitations and disabilities will be compared and contrasted with the outlined advantages and disadvantages. Finally, potential "barriers" in implementing such indexes will be reviewed and suggestions to overcome potential obstacles will be offered.

Low Back Syndrome and Nagi's Conceptual Scheme for Disablement

Whether the International Classification of Impairments, Disabilities, and Handicaps (ICIDH) or Nagi's disablement scheme are assessed, both represent a traditional pathology-oriented approach to disability, with the path to handicap or disability beginning with disease or active pathology. The Nagi disablement scheme is illustrated with specific reference to LBS in Figure 1. A brief definition of each term in the scheme follows:

Active pathology: interruption of normal processes coupled with the organism's inability to regain a normal state, examples of which include infection, trauma, metabolic imbalances, and degenerative processes.

Impairment: a loss or abnormality of an anatomical, physiological, mental, or emotional nature.

Functional limitations: restrictions in performance at the level of the individual.

Disability: restriction in the person's ability to perform socially defined roles.

Two important issues need to be considered when placing LBS within the framework of the Nagi disablement scheme. First, the active disease process in LBS continues to be extremely elusive. Second, although physical findings are an extremely important consideration, many studies of LBS support the presence of a strong nonphysical component (eg, psychosocial), which, when present, is indicative of multidisciplinary management. Each of these issues will be covered in greater detail with respect to its impact on the practicing physical therapist.

Low Back Syndrome: The Active Pathology

The increasing availability of sophisticated imaging technology has allowed diagnostic testing to become increasingly sensitive to underlying spinal pathology, presumably leading to easier identification of the "active pathology" in Nagi's model. Identifying a causative pathology in LBS, however, remains elusive. The most commonly implicated structural abnormalities of the spine involve some pathology of the intervertebral disk; yet, pathology of the disk is the cause of symptoms in only a small percentage of patients with LBS.[14] Structural abnormalities may even be quite profound without symptoms being present. For example, Ettinger et al[15] assessed the severity of spinal deformity ("wedge," "end plate," and "crush") using radiographic findings in 2,992 Caucasian women 65 to 70 years of age and found that even severe vertebral deformities account for only a small portion of troublesome back pain. Similar findings are obtained for pathology related to intervertebral disk height.[16] In addition to a lack of positive predictive value, structural abnormalities of the disk commonly have an unacceptably high negative predictive value, with several examples of studies in which unacceptably high false positive rates of spinal deformities are documented as a result of myelography,[17] computer-assisted tomography scanning,[18] magnetic resonance imaging,[19,20] and other radiological testing methods.[21,22]

Low Back Syndrome: Physical Impairments

Of particular importance to physical therapists are physical impairments that may predispose a person to future episodes of LBS or that may have resulted from a present or previous incident. In either case, intervention by the physical therapist for deficits in muscle performance, spinal mobility, and other physical impairments could conceivably have an effect on disablement provided that a strong relationship exists between physical impairment and disablement. Strong relationships between physical impairment and disablement, however, are not always the rule when patients with LBS are evaluated.[23] Waddell and Main[23] concurrently assessed physical impairment and disability and demonstrated convincingly the potential for disparity between physical impairment and disability in patients with LBS, especially those patients considered treatment "failure."

Whether or not psychological factors are contributing to disablement, it is generally agreed that measuring physical impairment in patients with LBS is important.[24] Physical impairments in LBS have been studied under three general designs: (1) longitudinal studies of subjects who are initially asymptomatic in which the predictive ability of physical impairments is evaluated, (2) concurrent studies in which resultant physical impairments are compared with findings of other evaluations (eg, disability) in groups who are symptomatic, and (3) studies in which the target of the intervention is the physical impairments of subjects with LBS.

Biering-Sorensen[25] measured a variety of anthropometric, flexibility, and muscle performance measures in over 900 subjects and followed them for a 1-year period. The author found that the modified Schober test[26] and a strain-gauge test of isometric back extensor endurance could be used to differentiate men with first-time episodes of "back trouble" from men who were free of back trouble. Biering-Sorensen also found that lower maximal voluntary force levels in backward extension and longer endurance times for back extension could be used to differentiate women with first-time episodes of back trouble from women who were free of back trouble. In both cases, however, the discriminant function based on the discriminant analysis of these tests when applied to the groups studied misclassified from 12.5% to 43% of the patients.

Searching for possible physical impairments that may predict future back problems is especially important in industrial and other work settings, presumably because preventive measures can be taken that will decrease the overall cost of LBS to industry. Cady et al[27] found that a low fitness level based on common physical measures such as muscle performance and cardiovascular endurance could be combined using an elaborate weighting procedure to predict which fire fighters would experience future back troubles. Battie and colleagues[28,29] studied flexibility of the lumbar spine and a maximal isometric lift test as possible predictors of low back pain in an industrial setting and concluded that both measures have little predictive capability for future back pain reports.

Waddell et al[24] evaluated 23 physical tests related to lumbar range of motion (ROM), spinal position (eg, lordosis, kyphosis), and various other lower-extremity strength and ROM measures in two groups, one asymptomatic and the other with chronic LBS. Although their factor analysis failed to demonstrate the dimension of physical impairment, they found that an "empirically" (nonscientifically or not based on a data analysis) derived combination of total flexion and extension and lateral flexion (using an inclinometer), spinal tenderness, average straight leg raising (in degrees of hip flexion), bilateral active straight leg raising (with the patient positioned supine, holding both heels and legs at least 15.2 cm [6 in] off the table), and a sit-up test could be used to differentiate between symptomatic and asymptomatic groups and explained 25% of the variance of their disability scores.

Attempts have been made to intervene using treatments targeting physical impairments in primary and secondary prevention as well as rehabilitation of patients with LBS.[30] An example of the latter was a series of studies by Mayer and colleagues,[31,32] who evaluated "functional restoration," a treatment that includes "specific exercises, training in functional tasks, education, and work simulation and work hardening" in addition to a psychological intervention that included pain management techniques, electromyographic biofeedback, and other cognitive-behavioral approaches. They found improvement in physical measures of flexibility and muscle performance as well as a substantially higher rate of return to work for persons who participated in the program as compared with those who did not. Some investigators have reported similar benefits with treatment programs primarily designed to address physical impairments in patients currently working but with a recent (<6-week) history of LBS that has caused them to lose time at work,[33] whereas others have reported less favorable results in programs with patients with chronic low back pain (average 8 years' duration).[34]

It appears that interventions designed primarily to focus on physical impairments have a tendency toward improved outcome provided the patients do not have a substantial psychosocial component to their LBS. Psychosocial issues will be discussed next.

Low Back Syndrome: The Psychosocial Component

There is good evidence supporting the fact that psychosocial and physical impairments are important considerations when evaluating and treating the patient with LBS. Deyo and Tsui-Wu[35] found that educational and income levels were better predictors of disability days" (days of activity limitation, absence from work, confinement to bed, or reduced housework) than physical findings and prescribed therapies. A variety of clinically administered tests designed to identify nonphysical components of the clinical examination (eg, magnified illness behavior, nonorganic factors, disability exaggeration, psychological distress) have been developed and shown not only to capture distinctly different information than traditional physical tests36 but also at times to better predict outcome than physical variables.[37-40] In addition, at least one prospective analysis has shown psychosocial issues (eg, job satisfaction) to better predict disabling injuries in the workplace than physical measures (eg, maximal lift capacity).[41]

Lack of Pathology and Psychosocial Component: Impact on Nagi Disablement Model

The lack of an identifiable disease process accurately accounting for functional limitations and disability has prompted some authors to characterize LBS as "an illness in search of a disease."[42] Such findings have led some researchers to identify the shortcomings of the traditional pathology model and offer alternative models that are not necessarily pathology driven.[43,44] One model, proposed by Waddell,[43] emphasizes treating LBS as a human illness (the total experience of disease as perceived by the patient) rather than as a disease (or active pathology), He describes illness behavior as "the observable and potentially measurable actions and conduct which express and communicate the individual's own perception of disturbed health," and he encourages clinicians treating patients with LBS to focus on measuring physical severity, psychological distress, illness behavior, and social interactions.[43]

How does an alternative model such as that proposed by Waddell relate to the Nagi disablement model? The answer depends on how the model is used to guide the management of patients with LBS. Certainly, the Nagi model can explain the various components of LBS, as Figure 1 depicts, by offering examples of each component of LBS as they relate to each component of the model. Similarly, specific examples of components of Waddell's clinical model based on illness can also find a place in the Nagi model.

Attempting to use the Nagi model in practice by strictly reading from left to right, however, may on the surface appear to have shortcomings, because there are so few cases in which an identifiable and accountable disease process is found in patients with LBS. By not identifying an "active pathology," those used to working within the traditional pathology framework are left with no specific management guideline at perhaps the most crucial point--the beginning.

Thus, two issues are brought form when active pathology and LBS are considered: (1) We should not expect much guidance from a diagnosis of pathology (if present) with respect to exactly what impairment, functional limitation, or disability will result from LBS, and (2) we should not expect the lack of a diagnosis of pathology to render a patient free from an "organic" reason for any impairments or functional limitations the patient may present. For those working within the Nagi formulation, lacking identifiable active pathology leaves clinicians working within the framework of the impairment, functional limitation, and disability portions of the model. Similarly, the alternative model proposed by Waddell was an attempt to move the clinician away from concentrating exclusively on disease and focus on the need to treat the patient and his or her illness.

The Case for Self-Reports in Low Back Syndrome

Deyo and Patrick[45] outline several "theoretical advantages" that support more broad use of patient self-reports within the health care system, including instances in which medical intervention results in improved patient outcome without concomitant improvement in disease status and, alternatively, instances in which disease markers and subsequent changes in them are not predictive of functional limitations and patient outcome. Both examples accurately depict the clinical situation commonly seen in patients with LBS, so it would seem that standardized self-reports could be most useful and should be an integral part of clinical settings in which patients with LBS are examined and treated.

Patrick and Deyo[46] distinguish between generic and disease-specific indexes of health status. Generic health status indexes are germane when a clinician is seeking information from a broad spectrum of subscales that make up the construct quality of life" and that include information from five major categories: (1) duration of life, (2) impairments, (3) functional status, (4) perceptions, and (5) social opportunities. Such subscales include both physical and nonphysical areas, so such scales would seem to be applicable to some patients with LBS, especially those who develop chronic LBP. Disease-specific measures of health status are shorter and target-specific components of quality of life and are used to assess specific diagnostic groups. in general, disease-specific indexes sacrifice comprehensiveness for better responsiveness (the ability to document clinically important changes) and are most useful in everyday patient care as well as clinical trials.

Deyo[47] has reviewed a number of generic and disease-specific (eg, low back pain specific) health status indexes for potential use in LBS, and some of the disease-specific indexes are listed in detail in the Appendix. A selected group of health status indexes are covered next. My rationale for the choice of indexes covered was based on the following two criteria: (1) that the index have good evidence of reliability and (2) that the index have at least some evidence of validity or has been shown to be responsive in clinical trials conducted with patients who have LBS, One generic index and four disease-specific indexes will be covered, and versions of all of the disease-specific indexes are included in the Appendix. Copyright limitations prohibit the inclusion of the generic index in the Appendix.

The Sickness Impact Profile 

Perhaps the most cited generic self-report for LBS is the Sickness Impact Profile (SIP). Originally attributed to Bergner and colleagues,[48] the SIP has become a well-established index used in a number of studies involving patients with LBS, including studies examining the treatment efficacy of bed rest[49] and transcutaneous electrical nerve stimulation.[50] The SIP is a comprehensive self-report that includes information from 12 subscales (ie, sleep and rest, eating, work, home management, recreation and pastimes, ambulation, mobility, body care and movement, social interaction, alertness behavior, emotional behavior, and communication). There is good evidence for the SIP'S validity in LBS based on the psychosocial and physical dimensions correlating with specific scales of the Minnesota Multiphasic Personality Inventory (MMPI) and a daily activity diary, respectively.[51] On the down side, the SIP includes over 100 items, takes 20 to 30 minutes to complete, and is somewhat cumbersome to score. By yielding a total score that can be divided into physical and psychosocial subscores, however, the SIP can be an extremely effective tool that can be used both to direct treatment and to document effectiveness, especially when the target population includes patients with a significant psychosocial component to their LBS.

The Roland and Morris Disability Index

Recognizing that administering the entire SIP can be too time-consuming in everyday clinical settings, Roland and Morris52 derived a "disability index" from 24 items on the SIP. By adding the phrase "because of my back" to each statement from the SIP, their resultant index became truly disease-specific (Appendix). No rationale for choosing the specific 24 items is offered. in addition, the Roland and Morris Disability Index also ignores the established scoring scale of the SIP and instead each answer is scaled simply 0 or 1, thus leaving a range of scores of 0 to 24. A subsequent study by Deyo,[53] however, revealed that the overall score from the Roland and Morris Disability Index was comparable to and provided as meaningful information as the overall SIP score but failed to capture a substantial component of the psychosocial dimension of the SIP.

The Oswestry Low Back Pain Questionnaire

Another disease-specific index is the Oswestry Low Back Disability Questionnaire, originally described by Fairbanks et al[54] and modified by Hudson-Cook et al[55] (Appendix). The Oswestry questionnaire is an easily administered self-report that results in an index of a patient's perceived disability based on 10 areas of limitation in performance (ie, pain intensity, the changing status of pain, personal hygiene, lifting, walking, sitting, standing, sleeping, social activity, and traveling). Each section is scored on a six-point scale (0-5), with 0 representing no limitation and 5 representing maximal limitation. The subscales combined add up to a total maximal score of 50. The score is then doubled and interpreted as a percentage of the patient-perceived disability (the higher the score, the greater the disability), The Oswestry index has been used in treatment efficacy studies involving manipulation and exercise as well as correlational studies of physical impairments and functional limitations.

The Waddell and Main Disability Index

For the generic and disease-specific indexes discussed, disability is defined as the inability or difficulty one has in carrying out functional activities. A more stringent definition of disability is used in the Waddell and Main Disability Index, in which disability is defined as the inability to carry out specific tasks without regard to the degree of difficulty.[36] These tasks include heavy lifting (> 13.6 kg [>30 lb], a heavy suitcase, or a 3- to 4-year-old child), sitting for >30 minutes, traveling in a car or bus for >30 minutes, standing for >30 minutes, walking for >30 minutes, sleep disturbances more frequently than three or four times per week, regularly missing or curtailing social activities, diminished frequency of sexual activity, and requiring help regularly with donning and doffing footwear. Although not published in self-report form, a questionnaire was easily composed by Rose et al[56] from the citation and is included in the Appendix, A positive response is recorded only if the patient cannot perform the activity, thus leaving no way to gauge the difficulty the patient has in performing the task. Only functional limitations are included, and there is no attempt to describe any psychosocial dimension of the patient's problem.

The Dallas Pain Questionnaire

The Dallas Pain Questionnaire (DPQ)[57] is a 16-item visual analog tool that attempts to describe four areas of disablement: (1) physical activities of daily living, (2) work and leisure activities, (3) anxiety and depression, and (4) social interests. A factor analysis of all components showed factor loading on two major components: "functional" and "emotional." Concurrent validity for the DPQ was established by correlating the "functional" and "emotional" scores to functional capacities (eg, physical demand characteristics of work) and MMPI scores, respectively. In both cases, significant correlations were obtained. The DPQ takes about 3 to 5 minutes to administer and purportedly takes less than 2 minutes to score.

Specific Uses for Self-Reports of Health Status in Low Back Syndrome Management

There are two major reasons to use self-reports in the everyday management of patients with LBS: (1) to provide specific guidance with reference to how to treat the patient and (2) to provide a patient-oriented outcome that should be reflective of important changes in the patient's health status. Thus, with regard to Nagi's disablement scheme, self-reports of health status can be used to provide information about the areas of impairment (both physical and psychosocial) and functional limitations and to assist in quantifying disabilities.

Regardless of the index used, the score from a health status measure can document the patient's perception of the severity of the low back incident. Clearly, we develop treatment strategies based on severity, with patients in acute distress treated with different approaches than those with less acute low back pain or those with chronic low back pain. Any high score on any of the indexes covered within this report can serve as an excellent first approximation that the patient perceives his or her condition to be acute.

Although self-reports are susceptible to bias, a biased high score can still be useful to the clinician. By comparing the score obtained from a self-report with physical impairment measures, the clinician can note disparities. In patients whose perceived disability is "out of proportion" with their diagnosis, pain, and physical impairment, Waddell and Main[23] Suggest either psychological distress or voluntary exaggeration is likely the cause. The physical therapist managing a patient with evidence of psychological distress should seek consultation from health care professionals trained in managing such conditions.

Individual components of some indexes can guide similar evaluation and treatment approaches. in the case of the SIP, for example, a physical score and a psychosocial score are obtained. In the case of the patient with acute low back pain, one could expect that the physical dimension score will exceed the psychosocial score, with the interpretation being the patient's management strategy can probably be predominantly physical in nature (eg, addressing physical impairments). Another patient, however, may score highly on the psychosocial dimension of the SIP, in which case nonphysical (eg, psychological) evaluation and intervention may be indicated.

In both cases described, follow-up SIP scores can also be used as a gauge of any therapeutic intervention. Thus, the SIP can serve as a tool for both guiding specific evaluative treatment strategies and gauging the outcome of any interventions. The same uses can be outlined for the disease-specific DPQ. Because of its ability to measure both physical and psychosocial dimensions of the patient's health status, the DPQ should be able to detect a psychosocial component to the patient's overall pain complaint, and, because of the precise scoring and documented reliability, any change in score should be truly reflective of a change in the patient's condition.

In reviewing the instruments and relating items to the Nagi formulation, one can see that there is an attempt at times to capture different elements of the model. For example, the Oswestry questionnaire, although labeled a disability questionnaire, actually includes measures of impairment (eg, pain), functional limitations (eg, sitting, lifting, standing), and disability (eg, personal care, sex life, traveling). In an attempt to obtain a representative index, one can make the argument that mixing different elements of the Nagi model in one index may confound any attempt to explain impairments, functional limitations, and disability using this particular index.

Impairments and the resultant functional limitations provide an initial approximation of a patient's ability to manage most everyday situations. In the final analysis, however, the relationship between the person's functional limitations and his or her disability will be moderated by the patient's needs and desires in life (Fig. 2). For example, given a set of functional limitations due to a back problem, a patient whose employment duties require lifting or heavy material handling will likely develop a greater disability than another patient with identical functional limitations but whose job is essentially sedentary. In both cases, however, quantifying the functional limitations in a meaningful fashion becomes an important component in disability determination, and health status measures are an excellent tool for a first approximation.

Barriers to the Use of Health Status Indexes

Health status measures appear to be in only limited use in physical therapy departments. Deyo and Patrick[58] cite barriers specific to the clinical use of self-reports, including conceptual/ attitudinal, methodological, and practical barriers. Of particular concern are the conceptual and attitudinal barriers, Like many health care professionals, physical therapists are not trained in the methods and philosophy behind the evolution of health status measures. Such a lack of knowledge often may lead physical therapists to perceive information gained from a health status questionnaire as "subjective" and not as worthy in the clinical decision-making process as "hard" measures related to physical impairments. In our health care system, physicians are trained to identify and treat diseases (diagnose); thus, following a traditional pathology model and successfully treating a patient's disease will eventually lead to return to desired activity (eg, no disablement). The physician trained and operating strictly within the traditional pathology model is closely paralleled by the physical therapist trained and operating with a strong emphasis on using physical impairments as a predominant source to guide as well as gauge the success of treatment. in both situations, if the disease process or the physical impairment is closely associated with patient outcome, then it is reasonable to assume that improvement in the disease or an improvement in the physical impairment should improve patient outcome.

Such is not always the case in LBS. At times, the patient with LBS who has a predominant physical component (eg, acute low back sprain) can most likely be managed primarily by the physical therapist, and in most cases independent of other health care professionals. In other cases, however, there appears to be no question that the physical impairment is only one component of the resultant illness that accompanies LBS. For the patient who is seen by the physical therapist as the primary caregiver and who has a psychosocial component to his or her LBS, the physical therapist has the obligation to recognize that the psychosocial component exists and to seek consultation from health care providers who are trained to evaluate and manage this component. The self-reports discussed can help in this determination.

This is not to say, however, that self-reports should be used with every patient who has LBS. Some would argue that too much time and energy are needed to administer a self-report to a patient whose clinical course is likely to be short (<6 weeks) and uncomplicated, with recovery likely to take place regardless of the particular intervention. The high cost of the relatively few failures, however, certainly argues in favor of characterizing impairments, functional limitations, and disability resulting from LBS using well-established indexes that are designed to be easily administered and scored in clinical settings and not relegating such information to the meaningless drivel often seen in the subjective portion of a problem-oriented medical record (SOAP).

References

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A Delitto, PhD, PT, is Assistant Professor, Department of Physical Therapy, School of Health and Rehabilitation Sciences, University of Pittsburgh, 101 Pennsylvania Hall, Pittsburgh, PA 15261 (USA)