Journal of Occupational Rehabilitation, VoL 6, No. 4, 1996
Predicting Post Treatment Spinal Strength and Flexibility in Work-Disabled Low Back Pain Patients Paul E Hickey, 1,4 Ann Marie Caroseila, 2 and Michael Feuerstein 3
This study examined whether posttreatment trunk strength and flexibility could be predicted from initial trunk strength and flexibility, age, gender, pain severity, diagnosis, length of work disability, return-to-work expectations, anxiety, and fear of reinjury among a group of 96 injured workers with chronic occupational low back pain who completed a multidisciplinary work rehabilitation program. The results indicate that initial average torque in trunk extension, age, gender, and average pain severity contribute significantly to prediction of final average torque in trunk extension. Initial average torque in trunk flexion, age, and gender contributed significantly to prediction of final average torque in trunk flexion, and age and initial range of motion contributed significantly to the prediction of final trunk range of motion. The results indicate that prediction of trunk strength and range of motion can be accomplished from measures of trunk strength and flexibility and pain obtained prior to the onset of rehabilitation. Psychological measures were not predictive of posttreatment trunk strength and flexibility. The ability to predict posttreatment trunk strength should facilitate clinical decision making in these complex cases. KEY WORDS: low back pain; rehabilitation; isokinetic strength testing; outcomes; therapeutic exercise.
INTRODUCTION
One of the primary goals of work rehabilitation is to facilitate a safe return to work by reducing the discrepancy between an individual's work capacity and the physical and psychological demands of the work environment. Several conceptual models have been developed to help identify multiple factors (sociodemographics, psychosocial, medical, and ergonomic) that influence the return-to-work process in individuals ]Occupational Rehabilitation and Ergonomics Center, University of Rochester Medical Center, Rochester, New York. 2Department of Social and Preventive Medicine, State University of New York at Buffalo, Buffalo, New York. 3Departments of Medical & Clinical Psychology and Preventive Medicine & Biometrics, Uniformed Services University of the Health Sciences. 4Correspondence should be directed to Paul F. Hickey, Occupational Rehabilitation and Ergonomics Center; University of Rochester Medical Center, 2337 Clinton Avenue S., Rochester, New York 14618. 251 I053-0487/96/1200-0251509.50/09 1996 Plenum PublishingCorporation
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with occupational musculoskeletal disorders (OMDs) (1, 2). One such model, the Rochester Model of Work Disability (2), proposes that a combination of medical status, physical capabilities, and work tolerances in relation to work demands and psychological and behavioral resources (worker traits, psychological readiness for work, ability to manage pain) contribute to the etiology, exacerbation, and maintenance of work disability associated with OMDs. This suggests that factors such as physical capacity in relation to work demands, psychological readiness to return to work, and pain management skills would be predictive of indices of functional improvement following work rehabilitation. Previous research has suggested that pain levels, distress, pain coping, pain behavior, somatization and expectations to return to work influence isokinetic trunk strength testing, and range of motion in work-disabled patients with occupational low back pain (3). The influence of these factors on rate of improvement in rehabilitation, however, has not been previously investigated. This study examined whether posttreatment trunk strength and flexibility could be predicted from initial trunk strength and flexibility, age, gender, pain severity, diagnosis, length of work disability, return-to-work (RTW) expectation, anxiety, pain behaviors, and fear of reinjury among a group of 96 work disabled patients with chronic low back pain. The ability to estimate an individual's spinal strength and flexibility following active work rehabilitation from measures obtained during initial evaluation could provide an empirical basis for judgments regarding the likelihood of an individual returning to his or her original job, and the potential need for physical conditioning and job accommodation or restructuring. In addition, the ability to predict final function should allow rehabilitation staff to set realistic, attainable goals at program onset and use these estimated goals as markers of progress throughout the course of a rehabilitation program.
METHODS
Ninety-six clients were referred for a Functional Capacity Evaluation (FCE) and rehabilitation at a multidisciplinary occupational rehabilitation center (see Table I for subject characteristics). All subjects were referred with the chief complaint of low back pain and had been unable to return to work despite conservative and/or surgical management. Only subjects with a diagnosis of sprain/strain or intervertebral disc disTable I. Subject Characteristicsa Males (N = 61) Females(N = 35) Age (yrs.) 36.89 (9.5) 33.63 (7.6) Body weight (lbs.) 192.89 (39.6) 171.77 (42.9)* Duration of work disability(mos.) 6.83 (5.7) 8.16 (6.7) RTW expectations(VAS, 0-10) 7.50 (2.9) 8.28 (2.5) Average pain (VAS, 0-10) 5.53 (2.3) 5.75 (2.3) Fear of reinjury (VAS, 0-10) 7.53 (2.6) 7.52 (2.6) Pain behavior (0-9 scale) 2.69 (1.6) 2.64 (1.4) aMean (standard deviation in parenthesis). *p < .05.
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order were included in the study. All subjects had been out of work a minimum of 3 months and were receiving Workers' Compensation benefits. Following the FCE, subjects entered a multidisciplinary active work rehabilitation program. Each program day consisted of physical conditioning, work simulation/conditioning, and work-related pain and stress management group sessions. Subjects completed an average of 30 sessions of rehabilitation. All subjects entered in the analysis fell within one standard deviation (SD = 5.0) from the mean number of rehabilitation sessions. This criteria was used to insure an equivalent range of training for all subjects. Additionally, all subjects met minimum force (10 ft-lb in either flexion and/or extension) and repetition (three complete repetitions of flexion and extension) thresholds during isokinetic trunk strength testing. Average torque in extension and flexion (ft-lb) and total range of motion (degrees of trunk extension measured from trunk flexion) were measured during the FCE and at the conclusion of the program using the Loredan Biomedical (West Sacramento, CA) isokinetic trunk dynamometer. Age, body weight (lb), gender, RTW expectation (4), (visual analog scale 0-10), average pain experienced over the week (VAS 0-10), fear of reinjury (5) (VAS 0-10), pain behavior scale-total score (6), duration of work disability (months from last worked to FCE), and anxiety (MCMI-II) (7) were assessed during the FCE. The isokinetic trunk dynamometer was used to measure trunk muscle performance in the sagittal plane. Subjects were positioned standing in the dynamometer with knees slightly flexed. The axis of rotation of the dynamometer was aligned with the subject's iliac crest. Stabilization was provided by a waist belt and a bolster on the anterior surface of the tibia just distal to the knee. The upper trunk was fastened securely inside a padded carriage attached to the lever arm of the dynamometer. The test speed used in this study was 30 degrees per second. Subjects were allowed five practice trials prior to the collection of data. Data collection at 30 degrees per second was based on three maximal repetitions of reciprocal flexion and extension following one submaximal repetition. The dynamometer was computer interfaced and provided a printout of the test results.
RESULTS Separate simultaneous multiple regression analyses were conducted to determine prediction equations for final trunk strength in extension and flexion, and range of motion using initial performance, weight, age, gender, RTW expectation, average pain, fear of reinjury, pain behavior, and months of work disability as predictors. Initial average torque in trunk extension, age, gender, and average pain contributed significantly to prediction of final average torque in trunk extension (R 2 = .63). Initial average torque in trunk flexion, age and gender contributed significantly to prediction of final average torque in trunk flexion ( R 2 = .64). Age and initial range of motion contributed significantly to the prediction of final range of motion (R 2 = .55). The results of the regression analyses are presented in Table II. Reduced multiple regression models were then run using only those variables found to predict significantly in the above analyses. Figure 1 presents the prediction
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Table H. Summary of Finding of Multiple Regression Analysisa Beta Variable
Constant Initial valueb Age Gender Average Body weight Mos from injury Work disability RTW expectation Fear of reinjury Pain behavior Anxiety Diagnosis
Final total Final average Final average trunk range of torque-extension torque-flexion motion 203.97* 1.08" -1.74" -36.57* -6.47* -0.04 0.11 0.26 2.32 2.36 -2.30 -0.23 -11.26
138.26" 0.78* -1.25" -27.29* -3.75 0.10 0.14 -0.48 1.73 2.19 -2.14 0.05 -13.76
76.32* 0.66* -0.52* -5.77 -1.73 -0.03 -0.08 -0.11 0.27 -0.79 -1.01 -(3.01 -0.27 aBeta is a standardized regression coefficient. Male = 1. female = 2, sprain/strain = 2, disc disorder = 3. blnitial value of specific outcome measure to be predicted. *p < .01. e q u a t i o n for p o s t t r e a t m e n t average torque in t r u n k extension, average torque in flexion and total t r u n k range of m o t i o n from initial average torque measures from these reduced models.
DISCUSSION T h e results indicate that prediction of trunk strength and range of m o t i o n can be accomplished from measures obtained prior to onset of rehabilitation. Such an approach should facilitate clinical decision making in these complex cases. T h e postt r e a t m e n t predictions could provide a basis for realistic goal setting with these patients as well as a vehicle to assess progress throughout a rehabilitation program.
Post treatment average torque in trunk extension = 203.97 + (1.08Xinitial average torque in extension) + (-1.74Xage) + (-36.57Xgender) + (-6.47Xaverage pain). Post treatment average torque in trunk flexion = 138.26 + (0.78)(initial average torque in flexion) + (-l.25Xage) + (-27.29Xgender). Post treatment total trunk range of motion = 76.32 + (0.66Xinitial range of motion) + (-0.52Xage).
Fig. 1. Prediction equations for posttreatment average torque in trunk extension, average torque in trunk flexion, and total trunk range of motion.
Work-Disabled Low Back Pain Patients
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The ability to set specific goals at the onset of activity should lead to improved performance during the physical conditioning activity (8). Although trunk strength and range of motion do not directly assess the ability to meet work demands, the ability to predict final strength and flexibility allows the clinician the ability to make more informed clinical judgments regarding the likelihood of the persistence of a discrepancy between the patient's strength and flexibility in relation to work demands. The findings indicate that pretreatment level of trunk strength and range of motion predict posttreatment levels. Lower scores at pretreatment are associated with lower scores at posttreatment, suggesting the need to pay particular attention to those with significant levels of trunk deconditioning during rehabilitation. Interestingly, those cases with higher levels of pain at pretreatment also demonstrated less improvement in trunk strength in extension at posttreatment. Carosella, Lackner, and Feuerstein (9) found that pain level can greatly interfere with program completion in active work rehabilitation for injured low back patients. It appears that pain can interfere with improvement in function as well, suggesting the need for such programs to more effectively address pain and its impact on outcome. Nachemson and Lindh (10) noted in an early study of trunk strength that "pain during the performance of the tests was found to be a probable strength reducing factor." The ability to predict posttreatment performance in light of both pretreatment reports of pain, and pretreatment trunk strength will allow better interpretation of pretreatment trunk strength results. Older subjects appeared to display less improvement in trunk strength and range of motion than younger subjects. A reduction in muscle mass, specifically loss of individual muscle fibers, may explain the decline in muscle strength with age (11). Therefore, it appears there should be lower expectations for older patients regarding improvement rate in contrast to younger patients. Female subjects exhibited less improvement in trunk strength and range of motion than males. In general, females have a lower percentage of muscle mass as compared to their male counterparts (11). The findings indicate that both the age and gender of the patient should be considered when determining goals regarding trunk function. The present findings should be considered in light of previous research. Whereas Papciak and Feuerstein (3) found a relationship between pretreatment return to work expectation, pain behavior, fear of reinjury, distress and trunk strength and flexibility, this study observed that initial trunk strength and flexibility and pain were significant predictors of change in trunk function. This suggests that psychological measures are associated with pretreatment performance at the time of testing, but do not appear to contribute to prediction of change of trunk strength or range of motion. It may be that such psychological variables affect dimensions of outcome other than trunk function. The best predictors of improvement of trunk function following rehabilitation are initial measures of trunk strength and flexibility. From a clinical perspective, the prediction model may prove useful in identifying patients who require more intensive efforts in physical conditioning and pain management. Additionally, the model can be used to identify clients with a lower level of trunk function who may require more intensive ergonomic intervention to reduce the discrepancy between work capacity and work demands.
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T h e p r e s e n t study should be replicated in a similar clinical sample o f low back pain patients in a diverse setting in o r d e r to provide further strength and generalizability o f the predictive model. Additionally, it would interesting to d e t e r m i n e the validity of the m o d e l in subacute low back p a i n cases. F u t u r e research should focus on o t h e r m e a s u r e s typically included in an F C E in an a t t e m p t to further aid in the prediction of a range of p o s t t r e a t m e n t o u t c o m e s (for example, return-towork, reduction of pain, increases in activities of daily living, r e d u c t i o n of psychological distress). Two d e m o g r a p h i c variables which c o n t r i b u t e d to the p r e d i c t i o n indicate that o l d e r workers and female workers will d e m o n s t r a t e the least improvem e n t following rehabilitation. Specialized ergonomic and rehabilitation p r o g r a m s should be directed toward these populations.
ACKNOWLEDGMENTS This research was s u p p o r t e d in part by a Research and D e m o n s t r a t i o n G r a n t f r o m the N a t i o n a l I n s t i t u t e on D i s a b i l i t y and R e h a b i l i t a t i o n R e s e a r c h ( G r a n t H133A00040) "Cost Benefit Analysis of Multidisciplinary W o r k R e h a b i l i t a t i o n in C h r o n i c L o w B a c k Pain R e h a b i l i t a t i o n . " T h e o p i n i o n s or assertions c o n t a i n e d herein are the private ones of the authors and are not to be construed as official or reflecting the views of the U n i t e d States D e p a r t m e n t of D e f e n s e or the Unif o r m e d Services University o f the H e a l t h Sciences.
REFERENCES 1. Cats-Baril WL, Frymoyer JW. Identifying patients at risk of becoming disabled because of low back pain: The Vermont rehabilitation engineering center predictive model. Sph~e 1991; 16: 605-606. 2. Feuerstein M. A multidisciplinary approach to the prevention, evaluation and management of work disability. J Occup Rehab 1991; 1: 5-12. 3. Papciak AS, Feuerstein M. Psychologicalfactors affecting isokinetic trunk strength testing in patients with work-related chronic low back pain. J Occup Rehab 1991; 1: 95-104. 4. Sandstorm J, Esbjornsson E. Return to work after rehabilitation: The significance of the patient's own prediction. Scand J Rehab Med 1986; 18: 29-33. 5. Feuerstein M, Papciak AS. Work reentry questionnaire. Center for Occupational Rehabilitation, University of Rochester School of Medicine and Dentistry, 1988. 6. Feuerstein M, Greenwald M, Gamache MP, Papciak AS, Cook EW. The pain behavior scale: Modification and validation for outpatient use. J Psychopathol Behav Assess 1985; 7: 301-315. 7. Millon T. Manual for MCMI-2 Minneapolis, MN: National Computer Systems, 1987. 8. Linstrom I, Ohlund C, Eek C, et al. The effect of graded activity on patients with sub-acute low back pain: A randomized prospective clinical study with an operant conditioning behavioral approach. Phys Ther 1992; 72: 279-290. 9. Carosella AM, Lackner JM, Feuerstein M. Factors associated with early discharge from a multidisciplinary work rehabilitation program for chronic low back pain. Pain 1994; 57: 69-76. 10. Nachemson A, Lindh M. Measurement of abdominal and back muscle strength with and without low back pain. Scand J Rehab Med 1969; 1: 60-65. 11. Astrand P-O, Rodahl K. Textbook of work physiology: Physiological bases of exercise (3rd Ed.). New York: McGraw Hill Book Co., 1986; pp. 342-344.
Predicting Post Treatment Spinal Strength and Flexibility in Work-Disabled Low Back Pain Patients Paul E Hickey, 1,4 Ann Marie Caroseila, 2 and Michael Feuerstein 3
This study examined whether posttreatment trunk strength and flexibility could be predicted from initial trunk strength and flexibility, age, gender, pain severity, diagnosis, length of work disability, return-to-work expectations, anxiety, and fear of reinjury among a group of 96 injured workers with chronic occupational low back pain who completed a multidisciplinary work rehabilitation program. The results indicate that initial average torque in trunk extension, age, gender, and average pain severity contribute significantly to prediction of final average torque in trunk extension. Initial average torque in trunk flexion, age, and gender contributed significantly to prediction of final average torque in trunk flexion, and age and initial range of motion contributed significantly to the prediction of final trunk range of motion. The results indicate that prediction of trunk strength and range of motion can be accomplished from measures of trunk strength and flexibility and pain obtained prior to the onset of rehabilitation. Psychological measures were not predictive of posttreatment trunk strength and flexibility. The ability to predict posttreatment trunk strength should facilitate clinical decision making in these complex cases. KEY WORDS: low back pain; rehabilitation; isokinetic strength testing; outcomes; therapeutic exercise.
INTRODUCTION
One of the primary goals of work rehabilitation is to facilitate a safe return to work by reducing the discrepancy between an individual's work capacity and the physical and psychological demands of the work environment. Several conceptual models have been developed to help identify multiple factors (sociodemographics, psychosocial, medical, and ergonomic) that influence the return-to-work process in individuals ]Occupational Rehabilitation and Ergonomics Center, University of Rochester Medical Center, Rochester, New York. 2Department of Social and Preventive Medicine, State University of New York at Buffalo, Buffalo, New York. 3Departments of Medical & Clinical Psychology and Preventive Medicine & Biometrics, Uniformed Services University of the Health Sciences. 4Correspondence should be directed to Paul F. Hickey, Occupational Rehabilitation and Ergonomics Center; University of Rochester Medical Center, 2337 Clinton Avenue S., Rochester, New York 14618. 251 I053-0487/96/1200-0251509.50/09 1996 Plenum PublishingCorporation
252
Hickey, Carosella, and Feuerstein
with occupational musculoskeletal disorders (OMDs) (1, 2). One such model, the Rochester Model of Work Disability (2), proposes that a combination of medical status, physical capabilities, and work tolerances in relation to work demands and psychological and behavioral resources (worker traits, psychological readiness for work, ability to manage pain) contribute to the etiology, exacerbation, and maintenance of work disability associated with OMDs. This suggests that factors such as physical capacity in relation to work demands, psychological readiness to return to work, and pain management skills would be predictive of indices of functional improvement following work rehabilitation. Previous research has suggested that pain levels, distress, pain coping, pain behavior, somatization and expectations to return to work influence isokinetic trunk strength testing, and range of motion in work-disabled patients with occupational low back pain (3). The influence of these factors on rate of improvement in rehabilitation, however, has not been previously investigated. This study examined whether posttreatment trunk strength and flexibility could be predicted from initial trunk strength and flexibility, age, gender, pain severity, diagnosis, length of work disability, return-to-work (RTW) expectation, anxiety, pain behaviors, and fear of reinjury among a group of 96 work disabled patients with chronic low back pain. The ability to estimate an individual's spinal strength and flexibility following active work rehabilitation from measures obtained during initial evaluation could provide an empirical basis for judgments regarding the likelihood of an individual returning to his or her original job, and the potential need for physical conditioning and job accommodation or restructuring. In addition, the ability to predict final function should allow rehabilitation staff to set realistic, attainable goals at program onset and use these estimated goals as markers of progress throughout the course of a rehabilitation program.
METHODS
Ninety-six clients were referred for a Functional Capacity Evaluation (FCE) and rehabilitation at a multidisciplinary occupational rehabilitation center (see Table I for subject characteristics). All subjects were referred with the chief complaint of low back pain and had been unable to return to work despite conservative and/or surgical management. Only subjects with a diagnosis of sprain/strain or intervertebral disc disTable I. Subject Characteristicsa Males (N = 61) Females(N = 35) Age (yrs.) 36.89 (9.5) 33.63 (7.6) Body weight (lbs.) 192.89 (39.6) 171.77 (42.9)* Duration of work disability(mos.) 6.83 (5.7) 8.16 (6.7) RTW expectations(VAS, 0-10) 7.50 (2.9) 8.28 (2.5) Average pain (VAS, 0-10) 5.53 (2.3) 5.75 (2.3) Fear of reinjury (VAS, 0-10) 7.53 (2.6) 7.52 (2.6) Pain behavior (0-9 scale) 2.69 (1.6) 2.64 (1.4) aMean (standard deviation in parenthesis). *p < .05.
Work-Disabled Low Back Pain Patients
253
order were included in the study. All subjects had been out of work a minimum of 3 months and were receiving Workers' Compensation benefits. Following the FCE, subjects entered a multidisciplinary active work rehabilitation program. Each program day consisted of physical conditioning, work simulation/conditioning, and work-related pain and stress management group sessions. Subjects completed an average of 30 sessions of rehabilitation. All subjects entered in the analysis fell within one standard deviation (SD = 5.0) from the mean number of rehabilitation sessions. This criteria was used to insure an equivalent range of training for all subjects. Additionally, all subjects met minimum force (10 ft-lb in either flexion and/or extension) and repetition (three complete repetitions of flexion and extension) thresholds during isokinetic trunk strength testing. Average torque in extension and flexion (ft-lb) and total range of motion (degrees of trunk extension measured from trunk flexion) were measured during the FCE and at the conclusion of the program using the Loredan Biomedical (West Sacramento, CA) isokinetic trunk dynamometer. Age, body weight (lb), gender, RTW expectation (4), (visual analog scale 0-10), average pain experienced over the week (VAS 0-10), fear of reinjury (5) (VAS 0-10), pain behavior scale-total score (6), duration of work disability (months from last worked to FCE), and anxiety (MCMI-II) (7) were assessed during the FCE. The isokinetic trunk dynamometer was used to measure trunk muscle performance in the sagittal plane. Subjects were positioned standing in the dynamometer with knees slightly flexed. The axis of rotation of the dynamometer was aligned with the subject's iliac crest. Stabilization was provided by a waist belt and a bolster on the anterior surface of the tibia just distal to the knee. The upper trunk was fastened securely inside a padded carriage attached to the lever arm of the dynamometer. The test speed used in this study was 30 degrees per second. Subjects were allowed five practice trials prior to the collection of data. Data collection at 30 degrees per second was based on three maximal repetitions of reciprocal flexion and extension following one submaximal repetition. The dynamometer was computer interfaced and provided a printout of the test results.
RESULTS Separate simultaneous multiple regression analyses were conducted to determine prediction equations for final trunk strength in extension and flexion, and range of motion using initial performance, weight, age, gender, RTW expectation, average pain, fear of reinjury, pain behavior, and months of work disability as predictors. Initial average torque in trunk extension, age, gender, and average pain contributed significantly to prediction of final average torque in trunk extension (R 2 = .63). Initial average torque in trunk flexion, age and gender contributed significantly to prediction of final average torque in trunk flexion ( R 2 = .64). Age and initial range of motion contributed significantly to the prediction of final range of motion (R 2 = .55). The results of the regression analyses are presented in Table II. Reduced multiple regression models were then run using only those variables found to predict significantly in the above analyses. Figure 1 presents the prediction
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Table H. Summary of Finding of Multiple Regression Analysisa Beta Variable
Constant Initial valueb Age Gender Average Body weight Mos from injury Work disability RTW expectation Fear of reinjury Pain behavior Anxiety Diagnosis
Final total Final average Final average trunk range of torque-extension torque-flexion motion 203.97* 1.08" -1.74" -36.57* -6.47* -0.04 0.11 0.26 2.32 2.36 -2.30 -0.23 -11.26
138.26" 0.78* -1.25" -27.29* -3.75 0.10 0.14 -0.48 1.73 2.19 -2.14 0.05 -13.76
76.32* 0.66* -0.52* -5.77 -1.73 -0.03 -0.08 -0.11 0.27 -0.79 -1.01 -(3.01 -0.27 aBeta is a standardized regression coefficient. Male = 1. female = 2, sprain/strain = 2, disc disorder = 3. blnitial value of specific outcome measure to be predicted. *p < .01. e q u a t i o n for p o s t t r e a t m e n t average torque in t r u n k extension, average torque in flexion and total t r u n k range of m o t i o n from initial average torque measures from these reduced models.
DISCUSSION T h e results indicate that prediction of trunk strength and range of m o t i o n can be accomplished from measures obtained prior to onset of rehabilitation. Such an approach should facilitate clinical decision making in these complex cases. T h e postt r e a t m e n t predictions could provide a basis for realistic goal setting with these patients as well as a vehicle to assess progress throughout a rehabilitation program.
Post treatment average torque in trunk extension = 203.97 + (1.08Xinitial average torque in extension) + (-1.74Xage) + (-36.57Xgender) + (-6.47Xaverage pain). Post treatment average torque in trunk flexion = 138.26 + (0.78)(initial average torque in flexion) + (-l.25Xage) + (-27.29Xgender). Post treatment total trunk range of motion = 76.32 + (0.66Xinitial range of motion) + (-0.52Xage).
Fig. 1. Prediction equations for posttreatment average torque in trunk extension, average torque in trunk flexion, and total trunk range of motion.
Work-Disabled Low Back Pain Patients
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The ability to set specific goals at the onset of activity should lead to improved performance during the physical conditioning activity (8). Although trunk strength and range of motion do not directly assess the ability to meet work demands, the ability to predict final strength and flexibility allows the clinician the ability to make more informed clinical judgments regarding the likelihood of the persistence of a discrepancy between the patient's strength and flexibility in relation to work demands. The findings indicate that pretreatment level of trunk strength and range of motion predict posttreatment levels. Lower scores at pretreatment are associated with lower scores at posttreatment, suggesting the need to pay particular attention to those with significant levels of trunk deconditioning during rehabilitation. Interestingly, those cases with higher levels of pain at pretreatment also demonstrated less improvement in trunk strength in extension at posttreatment. Carosella, Lackner, and Feuerstein (9) found that pain level can greatly interfere with program completion in active work rehabilitation for injured low back patients. It appears that pain can interfere with improvement in function as well, suggesting the need for such programs to more effectively address pain and its impact on outcome. Nachemson and Lindh (10) noted in an early study of trunk strength that "pain during the performance of the tests was found to be a probable strength reducing factor." The ability to predict posttreatment performance in light of both pretreatment reports of pain, and pretreatment trunk strength will allow better interpretation of pretreatment trunk strength results. Older subjects appeared to display less improvement in trunk strength and range of motion than younger subjects. A reduction in muscle mass, specifically loss of individual muscle fibers, may explain the decline in muscle strength with age (11). Therefore, it appears there should be lower expectations for older patients regarding improvement rate in contrast to younger patients. Female subjects exhibited less improvement in trunk strength and range of motion than males. In general, females have a lower percentage of muscle mass as compared to their male counterparts (11). The findings indicate that both the age and gender of the patient should be considered when determining goals regarding trunk function. The present findings should be considered in light of previous research. Whereas Papciak and Feuerstein (3) found a relationship between pretreatment return to work expectation, pain behavior, fear of reinjury, distress and trunk strength and flexibility, this study observed that initial trunk strength and flexibility and pain were significant predictors of change in trunk function. This suggests that psychological measures are associated with pretreatment performance at the time of testing, but do not appear to contribute to prediction of change of trunk strength or range of motion. It may be that such psychological variables affect dimensions of outcome other than trunk function. The best predictors of improvement of trunk function following rehabilitation are initial measures of trunk strength and flexibility. From a clinical perspective, the prediction model may prove useful in identifying patients who require more intensive efforts in physical conditioning and pain management. Additionally, the model can be used to identify clients with a lower level of trunk function who may require more intensive ergonomic intervention to reduce the discrepancy between work capacity and work demands.
256
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T h e p r e s e n t study should be replicated in a similar clinical sample o f low back pain patients in a diverse setting in o r d e r to provide further strength and generalizability o f the predictive model. Additionally, it would interesting to d e t e r m i n e the validity of the m o d e l in subacute low back p a i n cases. F u t u r e research should focus on o t h e r m e a s u r e s typically included in an F C E in an a t t e m p t to further aid in the prediction of a range of p o s t t r e a t m e n t o u t c o m e s (for example, return-towork, reduction of pain, increases in activities of daily living, r e d u c t i o n of psychological distress). Two d e m o g r a p h i c variables which c o n t r i b u t e d to the p r e d i c t i o n indicate that o l d e r workers and female workers will d e m o n s t r a t e the least improvem e n t following rehabilitation. Specialized ergonomic and rehabilitation p r o g r a m s should be directed toward these populations.
ACKNOWLEDGMENTS This research was s u p p o r t e d in part by a Research and D e m o n s t r a t i o n G r a n t f r o m the N a t i o n a l I n s t i t u t e on D i s a b i l i t y and R e h a b i l i t a t i o n R e s e a r c h ( G r a n t H133A00040) "Cost Benefit Analysis of Multidisciplinary W o r k R e h a b i l i t a t i o n in C h r o n i c L o w B a c k Pain R e h a b i l i t a t i o n . " T h e o p i n i o n s or assertions c o n t a i n e d herein are the private ones of the authors and are not to be construed as official or reflecting the views of the U n i t e d States D e p a r t m e n t of D e f e n s e or the Unif o r m e d Services University o f the H e a l t h Sciences.
REFERENCES 1. Cats-Baril WL, Frymoyer JW. Identifying patients at risk of becoming disabled because of low back pain: The Vermont rehabilitation engineering center predictive model. Sph~e 1991; 16: 605-606. 2. Feuerstein M. A multidisciplinary approach to the prevention, evaluation and management of work disability. J Occup Rehab 1991; 1: 5-12. 3. Papciak AS, Feuerstein M. Psychologicalfactors affecting isokinetic trunk strength testing in patients with work-related chronic low back pain. J Occup Rehab 1991; 1: 95-104. 4. Sandstorm J, Esbjornsson E. Return to work after rehabilitation: The significance of the patient's own prediction. Scand J Rehab Med 1986; 18: 29-33. 5. Feuerstein M, Papciak AS. Work reentry questionnaire. Center for Occupational Rehabilitation, University of Rochester School of Medicine and Dentistry, 1988. 6. Feuerstein M, Greenwald M, Gamache MP, Papciak AS, Cook EW. The pain behavior scale: Modification and validation for outpatient use. J Psychopathol Behav Assess 1985; 7: 301-315. 7. Millon T. Manual for MCMI-2 Minneapolis, MN: National Computer Systems, 1987. 8. Linstrom I, Ohlund C, Eek C, et al. The effect of graded activity on patients with sub-acute low back pain: A randomized prospective clinical study with an operant conditioning behavioral approach. Phys Ther 1992; 72: 279-290. 9. Carosella AM, Lackner JM, Feuerstein M. Factors associated with early discharge from a multidisciplinary work rehabilitation program for chronic low back pain. Pain 1994; 57: 69-76. 10. Nachemson A, Lindh M. Measurement of abdominal and back muscle strength with and without low back pain. Scand J Rehab Med 1969; 1: 60-65. 11. Astrand P-O, Rodahl K. Textbook of work physiology: Physiological bases of exercise (3rd Ed.). New York: McGraw Hill Book Co., 1986; pp. 342-344.
