Journal of OccupationalRehabilitation, Vol. 4, No. 4, 1994

Chronic Back Pain and Work Disability: Vocational Outcomes Following Multidisciplinary Rehabilitation M i c h a e l Feuerstein, 1,3 Lynne Menz, 1 T h o m a s Zastowny, 1 and Bruce A. Barron 2

Studies indicate that work disabled chronic back pain patients out of work for longer than three months have a reduced probability of returning to work. The escalating personal and economic costs (indemnity and health care) associated with such long term disability have facilitated efforts at multiple levels to prevent and more effectively manage work disability. Multidisciplinary rehabilitation (MDR) targeted at return to work represents one such approach. The approach is based upon a multidimensional conceptualization of work disability and integrates medical, physical, psychological educational and vocational interventions to increase physical function, reduce pain, increase stress coping skills and facilitate return to work. Seven outpatient multidisciplinary rehabilitation outcome studies for chronic back pain were identified that met the following selection criteria: 1) diagnosis of back pain, low back pain, spinal disorder (specific and nonspecific diagnosis), 2) chronic back pain of either longer than three months since injury or longer than three months absence from work, 3) use of an outpatient multidisciplinary rehabilitation approach that included some combination o f medical management, physical conditioning, pain and stress management, vocational counseling~placement and education regarding back safety and health, and 4) work reentry was the primary focus of outcome. These were reviewed to determine the effectiveness of MDR in terms of return to work outcome. Analyses revealed that an average of 71 percent of work disabled chronic back pain patients who completed a multidisciplinary rehabilitation program were working or involved in vocational rehabilitation efforts at 12 month follow-up in contrast to an average of 44 percent in corresponding comparison groups. While these studies suggest the clinical utility of a multidisciplinary approach as compared to usual care in facilitating return to work for chronic back pain patients, the literature was characterized by several methodological limitations including the absence of randomization in the majority of 1Center for Occupational Rehabilitation, University of Rochester Medical Center 2Division of Occupational and Environmental Medicine, University of Rochester Medical Center 3Correspondence should be directed to Michael Feuerstein, Ph.D., Center for Occupational Rehabilitation, University of Rochester Medical Center, 2337 Clinton Avenue South, Rochester, New York 14618.

229 1053-0487/94/1200-0229507.00/0 9 1994 Plenum Publishing Corporation

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studies, use of insurance company denials as control groups, heterogenous samples in terms of duration of work disability, job availability at discharge, extent of impairment and disability, age and duration of pain disorder, lack of specification as to exact treatment delivered in the control or usual care groups and varying definitions of return to work outcome. Research on predictors of return to work outcome following MDR were identified and included variables in five categories: demographics, medical history, physical findings, pain and psychological characteristics. The literature provides support for the use of integrated approaches that target the medical, physical, ergonomic and psychosocial factors that can exacerbate and~or maintain work disability. Future research should address current methodological limitations in the literature and focus on: 1) identifying critical treatment components of such approaches, 2) developing innovative screening methods to identify high risk cases to facilitate earlier more targeted efforts to assist such individuals, and 3) consider variations in the staging of various combinations of interventions in an effort to develop more cost-effective variations in the multidisciplinary approach. KEY WORDS: multidisciplinary rehabilitation; chronic back pain; spinal disorders; occupational diseases; work disability; outcomes; return to work.

INTRODUCTION Occupational musculoskeletal disorders and associated work disability represent a major challenge to primary and occupational health care providers. In the past decade, occupational physicians in particular have been confronted with an increasing demand to respond to the complex task of preventing long-term work disability associated with occupational musculoskeletal disorders. Legislative mandates at the national and international levels have firmly placed priorities on the need for more effective strategies in the prevention, evaluation and rehabilitation of work disability (e.g., Minnesota Workers' Compensation Treatment Standards:; Netherlands2; Feuerstein 19933). In addition, employers and third party payers of workers' compensation insurance expect and have increasingly demanded more effective outcomes in relation to return to work. While these trends are applicable to the full range of work-related musculoskeletal injuries and disorders, the activity-related spinal disorders continue to represent an especially prevalent and costly source of work disability 4,5. Several investigators have emphasized the multivariate nature of work disability associated with occupational musculoskeletal disorders of the spine (Feuerstein, 19916; Frymoyer & Cats-Baril, 19877, Chaffin & Fine, 19927). Prospective studies of factors related to work disability in patients with low back pain indicate that a combination of medical, psychosocial, vocational and socioeconomic variables appear to contribute to prolonged work disability or delayed functional recovery (Deyo & Diehl, 19889; Lancourt & Kettelhut, 1992:~ Werneke, Harris & Lichter, 199311). For example, in a series of 134 LBP cases all receiving workers; compensation, Lancourt and Kettelhut :~ (1992) reported that prior workers' compensation injury, higher Oswestry pain disability scores, longer time off work, living arrangements, relocation, poorer scores on a general coping measure,

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non-organic physical signs (verbal magnification, positive sciatic tension), organic/non-organic signs (variability of supine straight leg raise, gait problems) and organic physical signs (increased muscle atrophy) were predictive of work disability at six months following the index visit. A number of treatment approaches have been evaluated in relation to return to work of injured employees with occupational low back pain (Pope et al, 199112; Mayer et al 199113. These approaches have included single discipline interventions (e.g. primary care 13 physical conditioning [Lichter et al 198415; Werneke, et al 199311] multidisciplinary pain treatment (Cutler, et al 1994) 16, employer based rehabilitation (McElligott, et al 1989) 17, back schools (Linton, et al 1987) 18, work hardening (King, 1993) 19, and multidisciplinary work rehabilitation or functional restoration (Kinney, et al 1991) 2~ Given the potential role of medical, physical and psychosocial factors in the exacerbation and maintenance of work disability, (Feuerstein, 1991) 6 there has been a concomitant interest in the potential utility of treatment approaches that more comprehensively address each of these areas. These approaches typically involve a team of health care providers who direct intervention efforts at stabilizing the medical condition, enhancing functional capacity, increasing awareness of safe work behaviors, ergonomic risk factors, approaches to reduce such risk, and improving abilities to cope with pain and distress in order to facilitate a safe return to work. The approach is directed at occupational problem-solving/self management rather than a traditional medical model of care. While Fishbain et al (1993) 21 and Cutler et al (1994) 16 have recently published reviews on the effects of multidisciplinary pain center treatment on return to work, the present review focuses exclusively on multidisciplinary work or occupational rehabilitation that differs in relation to: theoretical foundations, treatment components, members of the health care team, intensity and duration of treatment and relative emphasis on occupational problems from most multidisciplinary pain center programs (Kinney, et al 1991) 2~ Also these previous reviews were not presented from the perspective of the occupational health care provider who is often confronted with very different challenges from the tertiary care pain specialist. The proliferation of occupational rehabilitation services in general and within occupational health clinics specifically highlights the need for increased awareness of the outcomes associated with such multidisciplinary rehabilitation as well as an appreciation for the limitations and future implications of this literature from both clinical and research perspectives. There is much concern among occupational health provider, insurance carriers and employers over the need for cost-effective approaches to facilitate return to work particularly in relation to work disability associated with delayed functional recovery in the work-related back patient. Outcome research should facilitate more reasoned input into the current controversies regarding the effective management of prolonged work disability (Feuerstein 1993) 3. A review of this literature may further our understanding of the complex interplay of medical, physical and psychosocial factors in the exacerbation and maintenance of work disability. This, in turn, can assist future efforts at developing more effective approaches to these com-

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plex work-related problems. It is with these goals that the present review of the clinical outcome literature on the effectiveness of outpatient multidisciplinary occupational rehabilitation and predictors of successful return to work following such interventions was undertaken.

METHODS A Medline search was conducted to identify disability studies for chronic back pain published between 1984 and 1994. Key terms used in the search included back pain, musculoskeletal disorders, occupational diseases, return to work and rehabilitation. The criteria for including an outcome study in this review was as follows: 1) diagnosis of back pain, low back pain, spinal disorder (specific and nonspecific diagnoses), 2) chronic back pain of either longer than three months since injury or longer than three months absence from work, 3) treatment included a multidisciplinary rehabilitation approach (also referred to as multidisciplinary occupational or work rehabilitation) that utilized some combination of medical management, physical conditioning, pain and stress management, ergonomic consultation, vocational counseling/placement and education regarding back safety and health (refer to Table 1 for a summary of the components often included in M D R ) , 4) treatment was provided on an outpatient basis, and 5) work reentry was the primary focus of outcome. There were an additional five (5) studies in the literature that assessed

Table 1. Components of Multidisciplinary Rehabilitation for Work Disability Secondary to Occupational Back Paina Psychoeducational/ PsychoMedical Physical social Ergonomic Vocational Further diagnostic evaluation

Therapeutic exercise/ physical conditioning

Cognitive- Worksiteergonomic behavioral job analysis therapy

Counseling

Medication management

Work conditioning/ simulation

Stress management

Placement

Redesignof w o r k station/workmethod to reduce risk

Physician education Physical therapy modalities

Pain manage- Assist with reasonment able accommodations

Case management/ follow-up

Back school

Retraining

Operant conditioning aNot all components were included in all studies. The list provides an overview of the components characteristic of the more comprehensive programs.

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the effects of multidisciplinary inpatient rehabilitation programs on return to work (Mellin, et al 199322; Altmaier, et al 199223; Estlander, et al 199124; Cassisi, et al 198925; McArthur, et al 198726). These were not included in the review. The rationale for exclusion of these studies is based upon the growing trend away from inpatient treatment of pain and disability particularly for occupational back pain given the higher cost of such interventions and absence of superior outcomes in relation to outpatient treatment. 4 For the purpose of this review, return to work is defined as: 1) return to pre-injury position full time, 2) return to any job (pre-injury, modified or new) part time or full time, or 3) participation state supported in vocational rehabilitation (counseling, training, placement). While there are many other outcomes resulting from multidisciplinary rehabilitation including improvement in function, pain and distress, the justification for selecting return to work as the exclusive outcome measure of interest in this review was based upon the following assumptions: 1) return to work represents an outcome measure with a relatively clear dichotomous endpoint (i.e. returrr--yes/no), 2) return to work is frequently the ultimate goal of rehabilitation of individuals with occupational back pain, 3) return to work can theoretically impact workers' compensation indemnity and medical costs and, 4) return to work can be associated with improved quality of life. It is important to note that some studies have included participation in state supported vocational rehabilitation services (counseling, placement and training) in their return to work rate figures. "Ready for vocational rehabilitation" was another measure of vocational outcome reported in one study. When vocational rehabilitation was included in the calculation of return to work outcome it is indicated in Table 2 and specified in Figure 1 that summarizes return to work outcome. While the original intent of this review was to identify outcome studies that included individuals with occupational low back pain receiving workers' compensation benefits, this was not feasible because all investigations did not include this group of patients exclusively. When data were available regarding specific information on diagnoses and compensation status this was provided in summary Table 2. Of the outcome studies published through March, 1994, 42 articles related to back pain rehabilitation were identified. Of these, seven (7) met the criteria stated above and were included in this review. Two of the seven articles (Mayer, et al 198727; Hazard, et al 199428) reported long term follow-up of the original studies in separate papers (Hazard, et al 198929; Mayer, et al 19873~ but were classified in this review as single studies because they reported new data from the longer term follow-up period. Five (5) studies evaluated outpatient rehabilitation programs exclusively (Hazard, et al 198929; Hazard, et al 199428; Mitchell, et al 199431; Mayer, et al 198727; Tollison 199132; Sachs, et al 199033). Two (2) additional studies evaluated both outpatient and inpatient programs (Fredrickson, et al 198834; Cairns, et al 198435). While the Fredrickson, et al (1988) 34 study did not specify the exact 40flen times inpatient treatment is reserved for the highly disabled patient with excessive levels of pain behavior, depression and narcotic analgesic abuse.

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number of cases in each type of program, it was decided to include the outcome from this study in the review because both outpatient and inpatient options provided the multidisciplinary rehabilitation approach described above. The Cairns, et al (1984) 35 study compared outpatient to inpatient intervention, and the data related to outpatient intervention were used in the review. The studies are summarized according to author, research design, subject selection criteria, treatment group intervention, comparison group intervention, work status methodology (i.e., point in time work outcome was measured and definition of return to work outcome) and outcomes in relation to return to work in Table 2.

RESULTS

Methodological Observations All seven studies utilized a prospective design. In contrast, only one out of the seven studies randomized subjects to treatment or control groups (Mitchell, et al 199431). The Mitchell, et al (1994) 31 study was not a complete randomization in that subjects with more severe illness behavior were referred to the treatment group. Across most studies there was a general tendency to assign individuals who were either denied access to treatment by their insurance carrier or program drop-outs to usual care groups. In general, these comparison or control groups were exposed to unspecified interventions, with possible access to physical therapy, medication, work hardening, back school, acupuncture, active exercise, manipulation or psychological intervention directed at enhancing pain and stress management skills. Studies included a variety of diagnostic categories ranging from nonspecific low back pain to specific discogenic disorders. The Mitchell study (Mitchell, et al 199431 ) also included non-back cases. While 77 percent of the treatment group and 78 percent of controls had "back" disorders Mitchell et al (1994) 31 reported that 23 percent of the treatment and 22 percent of the control group had "non-back" disorders. The authors defined "backs" as low back injuries involving the lumbar and lumbosacral regions and "non-backs" were soft tissue injuries to other "anatomical locations". The results of the literature as a whole did not distinguish diagnostic groups in terms of return to work outcomes. Prior history of surgical treatment, psychological disorders, litigation status, workers' compensation status and presence and duration of work disability varied across studies when specified. Type of work in terms of physical demands, job availability, accommodations availability, and insurance status (workers' compensation, SSDI, Medicaid) were not consistently reported across studies. The treatment rationale for the various multidisciplinary rehabilitation programs directed at return to work was reported in all studies. Treatment goals were also reported and generally included: 1) restoration of general physical function by increasing flexibility, strength and endurance, 2) improvement in work specific physical function, 3) enhanced pain management, 4) enhanced psychological coping

Research design

Toronto, Ontario

Comparison group: traditional care (not specified)

Controlled

Randomized

Mitchell et al., 1994 Prospective

Authors/date

Program length: 40 days (for 8 wk or 12 wk) or less

T = 271 (back injuries = 209)

Inappropriate illness Behavior (some)

Surgery: not appropriate Rx

Prior surgery: rare

Physical Avg. time since injury: Physical exercise (>90 days) Funct. simulation T = 142 days C = 129 days Psychoeducational Beh./cog. therapy Work disabled: from Education full time work Relaxation therapy Biofeedback Compensation: Counseling: ind. workers' comp. and group

Age: 45 yr T = 63% 37% C = 65% 35%

Chronic soft tissue and back injuries (not specified)

Selection criteria

Treatment group/ intervention

Physical therapy Medication Work hardening Back school Acupuncture Active exercise Manipulation Psychotherapy

Primary care: not specified

Program length: not specified

C = 271 (back injuries = 211)

Corn parison group/ intervention Results

Not modified or part time

RTW defn. Full time in preaccident job or new job

Working @ 12 mos. T = 79% (214/271) C = 78% (211/271)

Admission Working @ adm.: 0% Follow-up @ 12 mos.

Work status methodology

Table 2. Detailed Summary of Outcome Studies on the Effects of Multidisciplinary Rehabilitation on Return to Work a

Burlington, Vermont

Hazard et aL 1989 and 1994

Authors/date

Denied treatment by insurance co. and dropouts

Comparison group:

Controlled

Prospective

Research design

Workers' compensation T=93% C = 65% D/O = 100%

No psych, disorders

Surgery: not appropriate Rx

Work disabled (>4 mos.): Avg.: 19 mos.

C = 40 years D/O = 37 years

Avg. age: T = 38 years

Chronic LBP (not specified)

Selection criteria

Psychoeducational Stress mgmt./.biofeedback Beh. skills tmg. (gp., ind., family) Pain/crisis mgmt. Education

Physical therapy Exercise (stretching/relaxation, strength) Prog. weight training Gen'l. endurance and coord, training (recreation) Work simulation

Program length: 3 wk: 5.5 days/wk, 8 hr/day

T = 65

Treatment group/ intervention

Table 2. Continued

Treatment not specified

C = 20 D/O = 5

Comparison group/ intervention

Full time: >30 hours/week Same, lower or higher work demands

RTW Def'n.

Admission 12 mos. follow-up >5 year follow-up (avg. = 72 mos.)

Work status methodology

T = 63% (29/46) C = 3 5 % (6/:7) O/O = 0% (0/2)

Working @ 5 yr

T = 82% (53/65) C = 40% (8.20) D/O = 40% (2.5)

Working @ adm.: 0%

Results

Greenville, South Carolina

Tollison 1991

Comparison group: denied treatment by insurance co.

Controlled

Prospective

Compensation: workers' comp.

Prior surgery T = 28% C -- 29%

C = 12.6+5.6 mos.

C =20

Physical therapy Strengthening Flexibility exercises Work simulation Aquatics therapy

4 hr/5 dayAveek Treatment not specified (avg. = 18.4 days)

T = 54

Psychoeducational Behavioral mgmt. Avg. age Education T = 41.7 yr (32-51) Vocational counC = 42.6 yr (34-52) seling (ind. and group) Family counseling Work disabled since Pharmocotherapy injury/pain T = 11.2 +6.5 mos.

Occupational related chronic LBP Myofascial pain Degenerative disc disease Lumbar strain Spinal stenosis Spondylolithesis Bulging lumbar disc Arachnoiditis Undetermined RTW Def'n. not defined

Admission 12 mos. follow-up

T = 59% C = 20%

(26/44) (4/20)

Working @ 12 mos.

Working @ adm.: 0%

Concord, NH

Sachs et al., 1990

Au thors/date

reasons

Comparison group: (retrospective) Evaluated, but unable to participate for various

Controlled

Prospective

Research design

Compensation WC: 33 Private: 7 HMO: 2 Medicaid: 1 Self pay: 2

Chronic spine injury T = 45 Lumbar facet syndrome Program length: Lumbar radicular 4 wk: 3 days/wk, syndrome 4 hr/day Spondyloarthropathy Lumbar dysfunction Physical Disc fusion Stretching/relax. Strenghtening Avg. time work Weight training disabled: Endurance 11 mos. (2--84 Work simulation weeks) Psychoeducational Avg. age Nutritional T = 37 yr (23-53) counseling C = 34 yr (19-62) Back education Beh. modification Prior surgery: Psycho-social 46.6% (21) COUrtS.

Selection criteria

Treatment group/ intervention

Table 2. Continued

Treatment not specified

C =33

Comparison group/ intervention

Vocational tmg. reported separately

RTW defn. Same or different type of job

Admission Post treatment 6 mos. follow-up 12 mos. follow-up

Work status methodology Results

T = 3% (1/32)

Vocational tmg. @ 12 mos.

T = 63% (20/32) C = 42% (5/12)

Working @ 12 mos.

T = 59% (19/32) C = 33% (10/15)

Working @ 6 mos,

T = 75% (34/45)

Working Post Rx

Working @ Admission: 0%

Dallas, Texas

Mayer et al., 1985 and 1987

Syracuse, New York

Fredrickson et al., 1988

Comparison group: denied compensation from insurance co.

Controlled

Prospectve

Single group, no control

Prospective

Chronic LBP Degen. disc dis. Lumbar radicular lyndrome Postoperative epidural fibrosis Segmental instability Non-specific back pain

Litigation: 40%

Compensation Total: 50% Partial: 30%

Work status before treatment: N/A

Median time since disability: 35 mos. (3-216 mos.)

Chronic BP Organic findings: 38% No org. findings: 32% Prior surgery: 30% Avg. age: 30-39 years (20--69)

116

Psychoeducational Beh. stress regret. Cog./beh. skills

Physical Exercises Work simulation

Phase I: 3 wk/57 hr

T=

Psychoeducational Education Relaxation Biofeedback Vocational couns. Group and ind. psych, counseling Dietary and medication counseling

Physical therapy Exercise Occupational therapy (no passive modalities)

In or outpatient

Program length: 6 weeks: 5 days/wk

T=80

Treatment not specified

D/O = 11

C=72

No comparison group Vocational tmg. post Rx: T = 9% (6/71)

RTW as Goal: 71 of 80 cases

RTW Def'n.: Working or in vocational tmg.

3% 0% 9%

=

39% (24/62) D/O = 12% (1/8)

c

Working @ 12 mos. T = 81% (84/103)

T = 1.5% C = 1.5% D / O = 0%

Working @ admisAdmission 12 mos. follow-up sion 24 mos. follow-up Reg. Part time

RTW Def'n. Productively working Vocational tmg. reported separately

Working post Rx: T = 54% (38/71)

Post treatment

Authors/date

Research design

C = 93% D/O = 91%

T = 96%

Workers' comp.

Av. time work disabled T = 12 mos. C = 15 mos. D/O = 18 mos.

Avg. time since injury ( > 4 mos.) T = 25 mos. C = 21 mos. 19/0 = 27 mos.

Surgery: not appropriate RX

Avg. prior surgeries T = 1 C = 1 D/O = 1.5

Avg. age T = 43 C = 38 D/O = 44

Selection criteria

Avg. length: 5 wks

Phase I1:2 hr/day, 3 months) secondary to occupational back pain are associated with significantly higher return to work rates than usual care. It appears that the question can be answered affirmatively, albeit with qualifications. The multidisciplinary rehabilitation approach is associated with a 71 percent return to work rate (including state supported vocational rehabilitation) or 67 percent (return to work only) in contrast to 44 percent in the usual care or comparison groups. The 71 percent return to work rate should be considered in light of the chronic nature of the cases under investigation (mean duration of work disability = 16 months). The outcome figures, however, must be viewed with caution given the number of methodological limitations in this literature. The major threats to internal and external validity will be identified to assist future outcome research in correcting these methodological problems, thus allowing for more definitive conclusions regarding the effects of the approach. When feasible it is important for subjects to be randomly assigned to various intervention and control groups. Such randomization reduces the chances of selection bias. In cases where full randomization is not feasible, investigators may wish to consider the use of the minimum likelihood allocation (MLA) technique (Aickin, 198241). The technique sequentially assigns cases to groups in a clinical trial based upon some predetermined set of matching variables assumed to influence outcome. The technique

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minimizes pretreatment differences between groups on these measures. The findings from studies investigating predictors of return to work following multidisciplinary rehabilitation for chronic back pain can provide a very useful source of variables to consider when matching groups in future outcome research. As indicated in the results section, these variables fall into the broad categories of medical history, demographics, physical findings, pain and psychological characteristics. Although certain studies attempted to match on some of these variables, no single study considered the full range of potential confounding variables. Given the influence of these variables on return to work outcome it is important for groups to be balanced on these measures at pretreatment in order to more accurately determine the specific effects of the intervention(s) on return to work. Other methodological enhancements in future outcomes research include: 1) provision of clear description of diagnoses using ICD-10 criteria, 2) measurement and pretreatment levels of impairment and disability using standardized definitions and methodology, 3) detailed description of type, and intensity of "treatment" the control group receives, 4) use of no treatment or placebo control groups, 5) standardized and consistent definitions of return to work, 6) return to work outcome data that are validated against employer records rather than based solely upon self report from phone interview, 7) use of standard time intervals for follow up measurement (post treatment, 3 months, 12 months, 2 years post treatment), 8) data on regional unemployment rates for types of employment included in study and 9) specification of level and intensity of concomitant vocational or any other interventions in the clinic or at the worksite. Future studies should also include the extent of accommodations if provided, use of limited or restricted duty (occurrence and duration), data on relapse, specific causes of relapse (e.g., lay off, inability to perform essential job demands, pain, medical instability, etc.) and employer and patient response to return to work (i.e., problems with return). Data on cost-benefit of various intervention options should also prove useful in future policy determination and clinical decision making. The recent study by Mitchell et al (1994) 31 requires some elaboration given the large sample size and reported absence of differences between the treatment and "control" groups in order to avoid misinterpretation of the results. It is important to emphasize that according to Mitchell et al (1994) 31 the control group had access to many of the treatment components provided to the treatment group (e.g., physical therapy, work hardening, psychotherapy) although it is unclear as to the exact types and amount of treatment the control group received. Mitchel et al's (1994) 31 comments regarding the accessibility to similar treatments in the control sample and the rehabilitation strategy of the Ontario Workers' Compensation Board at the time the study was conducted which is to provide all injured workers with active therapeutic exercise once off work for a relatively brief period may limit the validity of the control group outcome and the conclusion of the study in relation to equivalent outcomes for treatment and control groups. In addition, the average time from injury to treatment was shorter (129 days) for the control group than the treatment group (142 days). This confounding variable could also have contrib-

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uted in part to the positive outcome observed in the control group given that duration of back pain is a predictor of return to work (Spitzer et al, 198740; Cairns, et al 198435). Lastly, patients with inappropriate illness behavior with continuing pain were referred to the treatment group which also questions the equivalence of the groups and placed a greater number of complex cases in the treatment group. Future research should insure that the control group does not receive similar treatments to the treatment group and that groups are balanced in relation to critical pretreatment characteristics that may effect outcome. While the predictors of vocational outcome studies have identified "prognostic" indicators for successful return to work, they have only been provided in relative terms (i.e., higher or lower values associated with positive outcome). Future research that refines the use of standardized, clinically useful methods of assessment of these indicators and specifies cut points or threshold levels could greatly assist clinicians in the decision making process regarding referral to such multidisciplinary rehabilitation programs for chronic work disabled back cases. Another clinical implication of the predictor studies is that future efforts can now focus on identifying the "high risk" case who will not respond and innovative alternative interventions could be developed and tested to facilitate a more positive outcome in these relatively more problematic cases. For example, if individuals with high levels of pain are more likely to drop out of such programs and/or less likely to return to work, more aggressive efforts at pain management, within the context of functional restoration, may be indicated to improve outcome in such patients (Carosella, et al 199439). Future treatment approaches that clinically identify specific risk factors for poor return to work outcome following multidisciplinary rehabilitation and directly target these factors for direct intervention may enhance outcome in these cases. Typically at present, it has been the authors experience that these high risk cases are referred for multidisciplinary rehabilitation only after many months of unsuccessful treatment where the risk factor for prolonged disability were not directly addressed. An alternative approach might be to provide such high risk cases with a set of interventions targeted at these "risk factors" prior to considering a more comprehensive rehabilitation program. If these patients respond to such treatment but continue to display a pattern of factors that justify a more intensive short term comprehensive rehabilitation approach it could be provided at that time. Evaluation of such stepped intervention efforts applied to "high risk" cases may result in a more cost effective approach to the more complex case. The present review did not attempt to include an analysis of the full range of treatment options available that assist patients in return to work (Nachemson, 199242) nor did it attempt to compare and contrast the diverse approaches. The results of the present review justifies the need to conduct future clinical investigations to determine the utility of these single intervention approaches in relation to multidisciplinary rehabilitation for chronic (3 months off work) work disability secondary to occupational back pain. Some less extensive variant of the multidiscipli-

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nary approach may also prove effective for select groups of subacute (3 months off work) patients. Given the positive outcome of the multidisciplinary approach, one logical next step in treatment development would be to identify which components of the multidisciplinary rehabilitation program are critical for return to work and other outcomes of interest (e.g., pain reduction, increased strength, flexibility, endurance, improved work tolerances, etc.). Such component analyses should assist in further refining treatment which represents another strategy to improve the cost-effective delivery of multidisciplinary approaches. From a clinical perspective, the development of more sophisticated evaluation protocols that assess specific medical, physical, psychological and ergonomic factors that interfere with a safe return to work followed by more precise tailoring of treatment in those specific areas, represents a potentially fruitful area of program development and outcomes research. Lastly, positive outcome following an intervention cannot provide definitive support for the etiologic role of the factors the intervention is assumed to modify. However, the present finding do provide additional empirical support for the suspected importance of such factors as physical deconditioning, inadequate pain and stress coping skills and insufficient knowledge and limited problem solving skills regarding back safety, health and ergonomics in the exacerbation and maintenance of work disability. Future efforts at prevention, evaluation and rehabilitation should continue to develop comprehensive yet cost-effective assessment and treatment variations that attempt to address the multiple factors contributing to work disability. It is through such efforts that the occupational health community can best meet the needs of the injured worker, the administrative systems that have evolved to manage work related pain and disability and the employer.

ACKNOWLEDGMENTS This paper was supported in part by the National Institute of Disability and Rehabilitation Research, Department of Education, Grant Number H133A00040, "Cost Benefit Analysis of Multidisciplinary Work Conditioning in Chronic Low Back Pain Rehabilitation", Michael Feuerstein, Ph.D., Principal Investigator. The authors would like to thank Jennifer Boehles for her assistance with manuscript preparation.

REFERENCES

1. State of Minnesota, Department of Labor and Industry. Emergency rules relating to workers' compensation: Treatment parameters. Minnesota Statues Section 176.83, subdivision 5, parts 5221.6010 to 5221.8900. 2. Ministry of Social Affairs and Employment, the Netherlands. Measures to reduce sick leave and improve labor conditions. Department of the Ministryof Social Affairs and Employment, Postbus 90801, 2509 LV Den Haag.

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