Definition: Mier 18 months duration, work-disability is considered permanent based on the low chance of return to work in this phase (see graph 2).
Significance: Permanent disability typically results in early retirement,
unemployment or entrance into a different profession. However, permanent separation from the pre-injury workplace happens in any of these ways at earlier phases too.
Frequency: About 4.5% of all claimants enter this state of permanent (partial or total) disability.90
Medical status: In Phase 8 major improvements in the ability to work based
on medical interventions are no longer anticipated by either the patient, medical professionals or others. A few patients may sign up for repeated heroic surgical procedures. Some live dependent on technical devices such as braces or TENS- devices (transcutaneous electrical nerve stimulation). Many patients are drug- dependent or suffer from other secondary psychiatric disorders including severe depression. A minority of patients receive interdisciplinary care in specialized pain clinics, some will be treated by alternative health care providers, and many will suffer silently. No data exist to describe the full personal and institutional disaster experienced by patients and care givers during this last phase.
Worker's compensation: In this phase worker's compensation claims are closed. Multiple medical reports and often litigation are conducted for a final decision about compensation. If the disability is accepted as work-related and if the
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condition is viewed as permanent, three different forms of compensation are available:
(i) "Temporary partial benefits": Compensation for employees who return to work at wages less than pre-injury wages.
(ii) "Permanent partial benefits": Compensation based on physician ratings of physical impairment in terms of percent loss of function ("scheduled"), or compensation based on earnings impairment ("non-scheduled").
(iii) "Permanent total benefits": The maximum amount of compensation available. Awarded if the illness precludes a return to customary employment or to any other work the patient is qualified for, or if rehabilitation is unsuccessful.
About one third of the total compensation funds are used for claimants with permanent disabilities.90
Interventions: The low chance of return to work in this phase as depicted in
graph 2 reflects the recent past and probably the average status quo. However, innovative interventions may have the potential to change this picture. For example, experiences with functional restoration programs-a combination of a sports medicine approach guided by objective measurement of physical function and combined with work simulation, pain management programs, and.various forms of counseling76 91 or combined with behavioral support programs81 -show some remarkable improvements in self-assessed pain,.depression, and work- disability among patients with at least 4 months (average of 12-19 months) of continuous disability: In one study, after one year, 86% of the program graduates were working or involved in occupational training programs. By comparison, only 20% of the dropout group and 45% of the comparison group were similarly employed.76 The participants were not homogenous with regard to duration of disability prior to enrollment and this factor was not analyzed in the study, but the
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results encourage further experimentation with biopsychosocial interventions in the late phases of disability.
Discussion
Usefulness of the Classification
According to the Quebec expert committee19 a good classification scheme should meet the following criteria:
(1) Biological plausibility. The classification is be compatible with current knowledge of vertebral physiopathology.
(2) Exhaustive property. The classification encompasses all cases seen in occupational health.
(3) Mutually exclusive categories: All cases, at any one point, fit into one and only one category; however, the patient may subsequently move into another category.
(4) Reliability, inter- and intraobserver reliability
(5) Simplicity efficiency, and safety. Use will be simple and will call neither for complex medical examinations nor encourage superfluous and/or potentially harmful investigations.
Quebec criteria 1-4 reflect a standard approach to an epidemiological classification and need not to be discussed further. All four are met by the proposed phase model. The fifth criterion, explicitly calling for safety and efficiency, is a novelty in a scientific classification system. Basically, this criterion grounds the classification in an ethical and economic context. The application of this criterion
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excludes, for example, the use of x-rays or modern imaging technics like computer- tomogram or NMR for any classification of back pain with only a few weeks duration. The argument is that these technics are inefficient at the early stages of disease, expensive, and constitute potential health hazards.
The proposed classification meets the fifth Quebec criterion since it relies solely on pain experience and working status. The use of medical examinations is reserved for clinical purposes. However, once clinical data are available, the phase model can be expanded by diagnostic subcategories within each phase for special investigations. In fact, the model provides a framework that can contain any medical classification of LBP as a subordinate element.
In addition to meeting these 5 criteria, a good scheme should be useful for a multidisciplinary approach to disability due to LBP. The value of a classification system depends on its potential usefulness. The potential usefulness depends on the tasks one wants to accomplish. In the case of occupational disability the task is to understand the disabling process as it occurs among employees with LBP in order to develop interventions to prevent work-disability. Since occupational disability is (i) a social phenomenon, but not limited to the work environment, and is (ii) related to chronic pain, but not limited to pathology, both research and intervention are multidisciplinary tasks. Therefore the classification must be useful to a broad spectrum of professions including medical, paramedical, psychological, legal, managerial, and technical occupations. Building upon the previous discussion of current classification systems for LBP and the description of distinct disability phases given above, eight additional criteria for a useful classification are proposed (Table 2). The next section describes how these criteria are met by the presented classification system.
Niklas Krause: Work-Disability and Low Back Pain p. 36
(1) Phase Specificity: Risk factors and interventions differ depending on the
particular time elapsed since injury. Therefore any classification system should be phase specific. Physical risk factors tend to be particularly important during early phases, while some psychosocial risk factors, like mental disorders or the presence of litigation, act predominantly in later phases.7 For most risk factors the phase specificity has still to be investigated, but the declining power of medical diagnosis and intervention in later phases of the disabling process is acknowledged by most re se a rch e rs.26 The Swedish study among sick-listed workers mentioned previously illustrates this point with regard to diagnosis. The decreasing effectiveness of medical interventions in later phases of disabling LBP are demonstrated by the decreasing proportion of patients returning to work (see graph 2).
(2) Psychosocial Plausibility: The classification should reflect the
development of the disabled role, the determinants of pain behavior, and the influences of the social environment, particularly the workplace, the compensation system, the medical system, and the family. The previous description of disability phases outlined important patient interactions with worker's compensation and with the medical system. The discussion of the chronic pain syndrome gives another example of the models psychosocial plausibility.
(3) Sociohistorical Flexibility: Categories should be defined so that
variations over time or between political systems can be absorbed without losing the ability to make cross-sectional and longitudinal comparisons. The phase model draws on social and legal conditions, current regulations and policies which all are subject to change. For example worker's compensation as described here draws
Niklas Krause: Work-Disability and Low Back Pain p. 37
mainly on the situation in the United States. Other countries especially in Europe use different systems, where some aspects of worker's compensation and disability insurance (e.g. wage loss substitution during work-disability) are guaranteed by universal health insurance. In the proposed classification the leading category
"duration of work-disability" allows for cross-cultural and longitudinal comparisons while accounting for certain social and historical conditions.
(4) Didactic Property: The classification system should help to organize
existing knowledge about risk factors, possible interventions, and costs of occupational disability. The proposed system is informative in the sense that it is organized around one simple main category (i.e. duration of work-disability) and leads stepwise to subcategories that require an increasing amount of special knowledge (e.g. surgical and non-surgical cases are broad medical categories positioned above categories of detailed diagnoses). Phases are organized based on typical sequences of social interactions during the disabling process thus providing a framework for the search for risk factors and for the direction of intervention strategies. The classification along subsequent phases of disability is also highly informative with regard to direct costs of disability, which increase with the duration of disability and with other parameters which are part of the classification system (e.g. surgery or litigation).
(5) interdisciplinary Usefulness: A classification scheme should facilitate
communication and coordination among researchers and practitioners, and should be usable by medical and non-medical professionals. The proposed classification system places interactions of the worker with different social and biological systems-i.e. with different areas of research and intervention-in a common framework of disability phases, thus outlining the areas of overlap between
Niklas Krause: Work-Disability and Low Back Pain p. 38
different disciplines and institutions. Since the model allows classification with and without detailed medical diagnoses, by people with and without medical training, with and without access to medical records or medical consultation, a multidisciplinary approach towards occupational disability is facilitated rather than hampered by the classification system.
(6) Signal function: A useful classification provides the basis for timely and
effective investigation and intervention by medical and non-medical groups.
Duration of work-disability could serve as an indicator for timely intervention since risk factors have differential relevance among the various disability phases as do patient evaluation methods and workplace intervention strategies. The proposed phases provide an outline of a framework, which would enable, for example, non- medically trained claim adjusters to infer from "time off work" when to suggest a medical reevaluation of the patient, rehabilitation or ergonomic redesign of the workplace. With the availability of more detailed information, even more precise subphases might be developed for different subgroups of injured employees or subcategories of jobs. Also, the model would be able to take advantage of clinical diagnoses, because once available, one might subgroup patients within each phase according to diagnosis.
(7) Hierarchical Structure: The most important and readily accessible facts
constitute the highest-level categories while less crucial and more detailed information requiring an increasing amount of investigation should be placed in subcategories. For example: The phase model is able to integrate detailed knowledge of a medical diagnosis as subcategories, but the primary categories do not depend on a series of medical procedures. Reliable classification is achieved
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at the highest-level category, i.e. duration of work-disability, which is the single most important variable and which is also readily accessible in most instances.
(8) Expandability: The classification system should be suitable as a
framework for current and future knowledge. The proposed classification achieves this by a two-fold open-endedness. First, the main variable is continuous (duration of disability) and allows for a flexible construction of phases and the insertion of subphases whenever more detailed knowledge arises (horizontal expandability).
Second, subcategories may be added at lower hierarchical levels as needed without requiring a change of the main categories (vertical expandability).
The basic feature of the proposed model is a continuous measurement of number of work-days lost. This allows for an exact and individualized positioning of each injured employee on this time-scale. For some purposes, this feature alone is useful. For example, compared to studies using categorical outcome measures for treatment, rehabilitation, job redesign and other interventions, the proposed classification provides a continuous outcome measure which is not only reliable, but also increases sensitivity and power.
It should be noted that the proposed phase model is imposed on a continuous disability process. In a sense, the definitions of specific phases may appear arbitrary, but, in fact, they are based on legal, social, and medical considerations, and on knowledge of the literature on LBP and disability, and on practical experience in the fields of conservative medical care, orthopedic surgery, rehabilitation, occupational medicine, workplace health promotion, epidemiology, public health, and health administration - both in North America and in Europe. Of
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course, the usefulness of specific cutpoints depends on who uses the data and for what purpose.
Expansion and Application
A first application of the model would be the description of risk factors and interventions for occupational LBP and disability and the relevance of these factors for each phase. In order to facilitate health promotion, such knowledge about risk factors should be organized by the socio-cultural system in which they occur or are going to be addressed. In the case of disabling back pain there are seven major systems that interact with each other and affect outcome: the individual, the non- occupational social environment, the occupational environment, the compensation and disability insurance system, the social security and welfare system, the health care (or medical) system, and the legal, political, and economic context.(graph 3).
Within each of these environments, subsystems can be identified, again preferably determined by the area of expertise or institutional access needed for research or intervention. Once the social systems and subsystems and their interactions have been described, phase-specific interactions of the patient and these systems can be systematically examined for the presence of risk factors contributing to the development of occupational disability.
For example, at any phase, risk factors present in the work environment could be sub-grouped as ergonomic (e.g. workplace design, physical work-load, vibration), organizational (e.g. shift system, job strain, quality of supervisory support), or motivational or attitudinal (e.g. job satisfaction). Risk factors attributed
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to the individual could be sub-grouped as demographic (e.g. age, sex), anthropometric (e.g. height), life-style-related (e.g. weight, smoking history, physical activity, fitness), psychological (e.g. coping style, life-cycle, mental disorders), or medical (e.g. abnormalities, history of LBP, comorbidity). Based on such lists for each system, researchers, and occupational health and safety professionals could make an informed decision on where to direct their resources.
Conclusion:
The suggested phase model of occupational disability due to LBP overcomes the limitations of biomedical models of LBP and takes the social and dynamic nature of disability into account. The simplicity of the classification system allows a crude assessment of the severity of back problems by all people dealing with work-disability, researchers as well as practitioners, with and without medical training, with or without access to medical records or consultation. At the same time the model is flexible and expandable enough to include detailed knowledge originating from the biomedical or social sciences, and the clinical as well as the occupational health and safety perspective. It is hoped that this model of disability will be useful in organizing knowledge as well as in guiding timely investigation and intervention.
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