Key Words: low back pain, disability, impairment, workersf compensation, physical therapy

Physical Therapy Outcomes for Patients ~eceiving workers' Compensation Following ~reatment for Herniated Lumbar Disc and Mechanical Low Back Pain Syndrome Richard P. Di Fabio, PhD, PT' George Mackey, MS, PT lames B. Holte, BS, PT2 onservative treatment of patients with low back syndrome who receive workers' compensation benefits typically consists of nonspecific interventions (1,8,13, 16,18,23,26,28,S4). Physical therapy provided to this population of patients is nonspecific when: l) the interventions are not designed to treat a particular area of the spine (ie., general strengthening, coordination exercises, and endurance training), and 2) the same treatment is provided to patients with different low back.syndrome etiology. The studies showing positive outcomes using this approach have reported return-towork rates on the order of 80% (IS, 18.28). In contrast, other nonspecific therapy programs have shown returnto-work rates below 50% (8,2534). When a nonspecific approach is used, it is difficult to generalize the treatment protocol to a particular diagnostic category because patients with widely divergent diagnoses are grouped together. Nonhomogeneous patient populations could, therefore, "dilute" the therapeutic effect because patients with a particular diagnosis may respond differently to treatment compared with patients with other types of low back syndrome etiology. Consequently, a Outcome of physical therapy for patients receiving workers' compensation may be related to a variety of factors, including the presence or absence of herniated lumbar intervertebral disc. The purpose of this study was to determine the level of disability, physical impairment, and rate of return-to-work for patients with disc disease and for those with mechanical low back pain syndrome without evidence of disc lesion. Twenty patients with disc disease and 22 patients with mechanical low back pain syndrome participated in this study. Physical therapy consisted of multiple interventions, including manual therapy based on the pattern of motion-provoked symptoms. The Oswestry disability questionnaire, fingertipto-floor distance, and maximum pain-free isometric static lih were measured at the initial evaluation, I month following the initial assessment, and at discharge from the clinic. Patients with disc disease did not show significant improvement in the mean Oswestry score or in forward bending, but did show increased static lih capacity. In contrast, patients with mechanical low back pain syndrome had a significant reduction in disability and significant improvements in fingertip-to-floor distance and maximum pain-free isometric static lih. At the time of discharge, 90% of the patients followed with mechanical low back pain syndrome returned to work in some capacity compared with 45% of the patients followed with disc disease. A physical therapy program with multiple interventions that includes treatment based on the pattern of motion-provoked symptoms appears to have the greatest benefit for patients with mechanical low back pain syndrome. Key Words: low back pain, disability, impairment, workersf compensation, physical therapy ' Professor, Director of Graduate Studies, Program in Physical Therapy, Department of Physical Medicine and Rehabilitation, 274 Childrens Rehabilitation Center, UMHC Box 388, University of Minnesota, 426 Church Street, S. E., Minneapolis, MN 55455 Partner, Physical Therapy Orthopaedic Specialists, Inc., Minneapolis, MN small therapeutic effect might result from combining nonsimilar patients who receive similar treatment (30). The classification of patients with low back syndrome is necessary to establish a prognosis and to provide a rationale for therapy (20). Classification based on etiology, however, is complicated by the fact that the cause of low back symptoms cannot always be identified (21 ). Many classification systems, therefore, have ignored the etiology of low back syndrome and based the treatment or prognosis on clinical signs and symp toms (4,6,19,29). The hallmark of mechanical low back pain syndrome is pain related to Volume 23 Number 3 March 1996 JOSFT

physical activity (31). Symptoms associated with mechanical low back pain syndrome are not typically related to a specific anatomic abnormality. Mechanical low back pain syndrome, therefore, is referred to as "nonspecific" low back pain. Patients with verifiable herniated disc who do not have stenosis in contrast represent a distinct clinical group that may require a different therapeutic a p proach compared with other types of low back syndrome (26). It appears that symptoms associated with herniated lumbar disc resolve without surgery, but the natural history of this resolution is on the order of 2 years (27). Therapy to reduce the prolonged convalescence in this patient population, therefore, is needed. It is not known, however, if current therapeutic approaches to managing patients with low back syndrome, such Patients receiving workers' compensation who have symptoms less than 6 weeks prior to the initial evaluation and high compliance with physical therapy have better outcomes. as those based on the pattern of pain-provoking motion (4,19), are equally effective for patients with and without herniated disc. Previous attempts to evaluate specific manual therapy techniques in patients with disc disease have not included or identified patients receiving workers' compensation (4,6,36). It is known that patients receiving workers' compensation who have symptoms less than 6 weeks prior to JOSPT Volume 23 Number 3 March 1996 the initial evaluation and high compliance with physical therapy have better outcomes (ie.. lower Oswestry scores or a greater frequency of return-to-work) compared to those with more chronic symptoms or low compliance (5). In addition, patients without leg symptoms have better outcomes compared to patients with lower extremity distal pain (5). The presence of pain radiating to the leg, however, does not necessarily indicate herniated disc because distal pain or paraesthesia can result from irritation of the lateral facet articulations or from lumbar ligaments (31). The influence of disc disease on the recovery of patients receiving workers' compensation, therefore, has not been clarified. The purpose of this outcome study was to describe the level of disability, physical impairment, and rate of return-to-work for compensated workers before and after the completion of a physical therapy treatment program. Physical therapy consisted of multiple interventions, including manual therapy based on the patterns of movement that provoked symptoms. The outcomes for two distinct diagnostic groups were evaluated: patients with herniated lumbar intervertebral disc and mechanical low back pain syndrome. METHOD Subjects Patients in this study were receiving care at Physical ~ h e iortho- a ~ ~ paedic Specialists Inc., a private practice clinic in Minneapolis, MN. The protocol for this study was approved by institutional review at Physical Therapy Orthopaedic Specialists Inc., and by the Committee on the Use of Human Subjects at the University of Minnesota, Minneapolis, MN. Patients were evaluated prospectively and the procedures did not differ from routine clinical practice. Subjects were included in this analysis if: I) their primary complaint was low back pain, 2) the diagnosis provided by the referring physician was either herniated disc (confirmed by neurologic examination and by magnetic resonance imaging or computerized tomography when indicated) or mechanical low back pain syndrome with no objective evidence of herniated disc, and 3) the patients were receiving workers'compensation and signed a consent form. Patients were excluded from the study if they had previous back surgery or a diagnosis of spinal stenosis, tumor, or systemic disease. All patients meeting the criteria were evaluated without preselection. A total of 42 patients met the criteria, and the characteristics of each diagnostic group are outlined in Table 1. Physical Therapists Providing Care Fifteen physical therapists (average of 13 years of experience, SD = 6 years; range = 5-27 years) performed the initial evaluations, treatment, and discharge assessments. When joining the clinic staff, each therapist completed a postgraduate internship program involving up to 6 months of didactic and clinical work related to the assessment and treatment of musculoskeletal disorders. In addition, each therapist completed several continuing education courses in manual therapy and was required to pass a practical exam administered at the clinic that indicated proficiency in this area of care. Description of Outcomes The assessment and treatment protocols used in this study were identical to those implemented in a previous study of routine care for patients with a primary complaint of low back pain (5). The description of outcomes, reliability, and treatment procedures from our previous work (5) is outlined below. During the initial assessment, the subject indicated the duration of low back pain and pain history. One disability outcome

Specific treatment decisions were guided by the summary of significant findings for each patient. * Consecutive days with at least some pain prior to initial evaluation. t Number of treatment sessions atrended/number of treatments scheduled x 100. DISC = Herniated disc disease. MLBPS = Mechanical low back pain syndrome. 85% 89% 14% 11% 53-100 /o 67-1 00% TABLE 1. Characteristics of patients with herniated disc disease and mechanical low back pain syndrome. measure (Oswestry score) and two physical impairment outcome measures (fingertipto-floor distance and maximum isometric pain-free lift) were evaluated. The Oswestry Low Back Pain Questionnaire is a self-report instrument that evaluates perceived disability in 10 areas (sub-scales), including pain intensity, the ability to sit, stand, sleep, and complete activities related to personal hygiene (7). Each subscale is rated from 0 (no limitation) to 5 (severe limitation). The total maximum score [50] is doubled and reported as a percent of the patient's perceived disability. Higher scores indicate greater disability. Serial fingertipto-floor measurements have been used previously to assess the efficacy of treatment for low back pain (5,12,15,16,24). A single trial was done here to measure the fingertipto-floor distance. Previous work has shown that patients who have an increase in pain on the first attempt show greater fingertiptofloor distance (less motion) com- pared with patients who do not report pain during forward bending (1 0). The first attempt, therefore, provides a measurement that appears to be sensitive to symptom provocation. The patient was asked to stand in a comfortable position and to bend forward as far as possible without bending the knees. The distance of the middle finger to the floor was assessed using a tape measure marked in 0. l km increments. Maximum isometric pain-free lift has been previously used as one measure of work capacity (3,5,18), and norms have been published by gender for nonback-injured subjects working in industry (3). During the maximum pain-free isometric static lift assessment, each subject was tested using a spring-loaded dynamometer attached to a level wooden platform. The range of operation was 0 Newtons (N) to 2,844 N with 22.22 N increments. The patient was instructed to stand on the platform, pick up the dynamometer handle, and pull upward on the handle as much as possible without causing pain or modifying existing symptoms. The dynamometer handle was fixed at 38 cm from the platform base in order to standardize lift height. A single trial was collected for the maximum pain-free isometric static lift because the therapists were seeking a conservative measure of this parameter that was minimally influenced by pain and repetitive learning. The patients were able to choose the posture that was most comfortable for the lift. In addition to the disability/physical impairment outcomes, returnand release-to-work status were evaluated. Return-to-work status was determined by the referring physician in consultation with the patient. The decision to return to work in some capacity was based primarily on the amount of improvement in the patient's symptoms and functional capacity. Release-to-work might differ from actual work status because the patient might have been able to work in some capacity, but could not secure employment that would accept personnel with physical limitations. All outcome measures were recorded together with the anamnestic data in the patient's chart. The disability, physical impairment, and work-related outcome measures were obtained at the initial assessment, 1 month from the initial assessment, and at the time of discharge from the clinic. The time to discharge was variable between subjects. The range of days spanning initial evaluation to discharge was summarized for each diagnostic group (Table 1). Volume 23 Number 3 March 1996 JOSFT

Reliability of Outcome Assessments The reliability of the outcome assessments used in this study has been reviewed in detail elsewhere (5). Test-retest correlations above r = 0.90 on the Oswestry questionnaire indicate that this tool provides a reliable measure of the patient's percep tion of disability (7). Gauvin et al (1 0) reported intra- and intertherapist intraclass correlation coefficients of 0.98 and 0.95, respectively, for fingertiptefloor distance measurements. Provocation of symptoms in some patients during forward bending did not influence the reliability of the measurement. Norms for maximum isometric lift have been reported in research sponsored by the National Institute for Occupational Safety and Health (3). Chaffin (3) calculated the reliability of maximum pain-free isometric static lift for 446 males and 105 females using a testretest coefficient of variation. The range of variation that could be expected with repeated measurements was 513% (3). Zeh et al (35) found that more than 80% of the betweensubject variability (r2) on mean painfree static lift capacity for three trials was explained by the first lift in nondisabled workers. It was concluded that a single lift provided a reasonable and predictable measure of static lift capacity (35). Treatment Procedures Physical therapy treatment had multiple components, including spinal mobilization, active exercise, passive stretching, heating modalities. and lifting instructions. Specific treatment decisions were guided by the summary of significant findings for each patient. The significant findings generally included a description of pain/symptom-provoking motions and an assessment of passive and active motion of the spine, posture, and strength. Active exercise programs were developed based on the pattern of JOSF'T Volume 23 Number 3 March 1W6 pain/symptom-provocation during active motion, the pattern of muscle weakness in the trunk and lower extremities, and the pattern of limitations in passive motion. In general, patients received active exercise programs that were designed to facilitate spinal motion and reduce symptom severity. McKenzie's protocol ( 19). for example, was widely used to provide extension mobilization exercises for patients reporting relief of symp toms with back extension. In addition, extension mobilization exercises were used with patients who had a limitation of motion in this direction. The decision to provide passive joint mobilization (graded articulation) was based on the finding of segmental hypomobility that was thought to be related to the primary complaint. Individual therapists provided a range of mobilization procedures, but these treatments were generally administered as described by Maitland (1 7). Muscle contraction-relaxation techniques were also used to improve motion as described by Greenman (1 1). Briefly, patients were positioned by the therapist to the point of resistance to spinal motion and then asked to provide a graded, nonpainful isometric contraction. The patient was repositioned by the therapist after each contraction so that the posture of the patient could be maintained at the point of resistance. This procedure was designed to facilitate gradual increments in spinal range of motion. The number, magnitude, and duration of the contraction-relaxation cycles varied according to the tolerance of each patient. Therapeutic modalities (ie., ultrasound, electrical stimulation) were provided at the discretion of each therapist and were used to reduce pain and facilitate the patient's response to treatment. All patients in this study were referred to a functional activities training class. This class consisted of a I-hour video that reviewed basic spinal anatomy, mechanics, various types of spinal injury, and common spinal surgeries (ie., segmental decompression). The video was followed by a 90-minute group session that reviewed proper lifting and loadcarrying techniques. In addition, proper sitting and standing postures were demonstrated as well as the use of back supports and cushions (22). DATA ANALYSIS Equivalence on Baseline Characteristics A chi-squared statistic with a Yates correction was used to compare the distributions of gender and duration of symptoms (ie., acute vs. chronic) between disc disease and mechanical low back pain syndrome groups (Table 1). Acute low back syndrome was defined as a report of pain on continuous days for less than 6 weeks prior to the initial evaluation. Two-group t tests were used to compare mean age, number of treatments, total days spanning all treatments, and level of con~pliance between groups (Table 1). Analysis of Physical Therapy Outcomes An a primi analysis was conducted using paired t tests with a Bonferroni correction for multiple comparisons. Disability (Oswestry scores) and physical impairment outcomes (fingertip to-floor distance and maximum painfree isometric static lift) were compared for each diagnostic group at the initial assessment vs. 1 month and at the initial assessment vs. the discharge assessment. The number of patients who returned to work in some capacity or were released to work in some capacity at 1 month and discharge was evaluated using a chi-squared statistic with a Yates correction. All data analyses were done using the Biomedical Diagnostics Programs (BMDP) statistical computing software (version PC90). Several cases had missing (unrecorded) data, but

Initial 1 Month N Initial Discharge N Oswestry (%I DISC 41 (19) 38 (21) 18 41 (20) 38 (22) 8 MLBPS 43 (12) 33 (18) 15 32 (17) 23 (21)' 10 FTFD (cm) DISC 33 (21) 28 (23) 15 28 (24) 20 (19) 11 MLBPS 36 (21) LlFT (N)* 19 (16)' 17 36 (25) 15 (18)* 10 DISC 453 (351) 613 (382)* 11 471 (351) 884 (417)' 7 Male 547 (360) 725 (378)t 8 471 (351) 884 (417)' 7 Female 209 (187) 316 (227) 3 - MLBPS 275 (284) 497 (337)* 15 559 (409) 768 (422)t 7 Male 369 (347) 658 (378)' 8 596 (436) 845 (414)t 6 Female 169 (156) 316 (165)* 7 356 (000) 334 (000) 1 * Within group comparison: initial vs. 1 month or initial vs. discharge; p < 0.025. t Trend toward statistical difference; p between 0.027 and 0.06. * Norm for males = 543 N, norm for females = 267 N, based on the results from Chaffin (3). DlSC = Disc disease. MLBPS = Mechanical low back pain syndrome. FTFD = Fingertip-to-floor distance. LlFT = Maximal pain-free isometric lift. TABLE 2. Mean (SO) Oswestry score, fingertipto-floor distance, and maximal pain-free isometric lift for patients with disc disease and mechanical low back pain syndrome. were analyzed with a "flag" inserted into the data set to indicate a missing entry. Unrecorded data accounted for the fluctuating number of sub jects analyzed for any given variable (Table 2). RESULTS Equivalence on Baseline Characteristics There were no significant differences between groups with regard to any baseline characteristic (Table 1). The Yates corrected chi-squared statistic for duration of symptoms (x' = 3.23, df = 1, p = 0.07), however, showed a trend toward a higher frequency of patients with acute pathology in the mechanical low back pain syndrome group. Analysis of Physical Therapy Outcomes Patients with herniated disc disease did not show improvement in the mean Oswestry score at 1 month or at discharge (Figure 1). Forward bending also did not show improvement between initial assessment and 1 month or between initial assessment and discharge (Table 2). Maximal isometric lift capacity, however, increased significantly by 1 month and discharge (Table 2). The mean pain-free static lift capacity at the initial evaluation for males with disc disease was very close to the norm lift capacity of 543 N (3). Females with disc disease initially had pain-free static lift capacities substantially below the female norm of 267 N (3). Following physical therapy treatment, however, males and females with disc disease substantially exceeded the norm lift capacity. Patients with mechanical low back pain syndrome had a significant reduction in disability scores at discharge (p < 0.025) compared with the initial assessment (Figure 1, Table 2). The patients in this group also demonstrated greater forward bending (a decrease in fingertiptofloor distance) and marked improvements in isometric lift capacity at both the 1-month and discharge assessments (Table 2). Both males and females in the nonspecific back pain group had lift capacities below gender-based norms at the initial evaluation (Table 2). After physical therapy intervention, males and females with mechanical low back pain showed nearly a two-fold increase in static pain-free lift capacity at the 1-month reassessment (Table 2). The number of patients released to work in some capacity differed significantly between mechanical low back pain syndrome and disc disease. At 1 month, 13 of 15 patients with mechanical low back pain syndrome were released to work in contrast to six of 14 patients with herniated disc disease (x' = 4.37, df = 1, p < 0.05). At the time of discharge, 10 of 10 patients with mechanical low back pain syndrome were released to work compared with five of 11 patients with herniated disc disease (x2 = 5.20, df = 1, p < 0.05). There was no statistical difference in the return-to-work rate between groups at 1 month (x' = 2.17, df = 1, p = 0.14). At the time of discharge, however, nine of 10 patients with mechanical low back pain syndrome were working in some capacity compared with five of 11 patients with herniated lumbar disc disease (x' = 5.07, df = 1, p = 0.02). Regarding missing (unrecorded) data for release-to-work status at the 184 Volume 23 Number 3 March 1996 JOSPT

100 80 h C 60 >r.c, L cn 8 40 20 0 DISC MLBPS 1 Month W Discharge IGURE. M ea n Oswestry scores at the initial assessment, 1 month following the initial assessment, and at the time of discharge for patients kith herniated lumbar intervertebral disc (DISC) arid mechanical low back pain syndrome (MLBPS). Lines above each bar represent the standard deviation. 1-month assessment, seven patient. with mechanical low back pain syndrome and six patients with disc disease were lost to follow-up. At discharge, 12 patients with mechanical low back pain syndrome and nine patient5 with disc disease were lost to follow-up. DISCUSSION Patients receiving workers' compensation with mechanical low back pain syndrome appeared to benefit from a physical therapy program based on the pattern of symptomprovocation, whereas the subject$ with herniated disc disease did not show a significant reduction in the level of disability (Figure). In addition, a significantly greater proportion of patients with mechanical low back pain syndrome were released to work or returned to work compared with the disc disease group. These results suggest that patients with herniated disc have poorer short-term outcomes than patients with mechanical low back pain syndrome. It is possible that patients in the disc disease group may respond to therapy but over a longer period of time. Patients in the disc group were followed for a maximum of 3.5 months (initial assessment to discharge) (Table 1). Saal and Saal (26) followed subjects with herniated lumbar disc for over 2 years and 92% returned to work. Only 22% of their patients (I3 of 58), however, were receiving workers' compensation. The prolonged convalescence in the disc disease group might be related to the time required for reabsorption of herniated disc fragments (27). Fryrnoyer found that the duration of disability was a strong predictor of outcome (9). One possible reason for this finding is that there may be less illness behavior associated with acute vs. chronic back pain (32, 33). In addition, it may be that early intervention may influence therapeutic outcome in a positive way. It was reported previously that subject$ receiving workers' compensation with acute symptoms had lower disability scores and higher return-to-work rates at discharge compared to those with chronic symptoms (5). The group with mechanical low back pain syndrome in the current study tended to have proportionally more acute cases (Table l), and this might have contributed to the lower disability and higher release and return-towork rates for patients with mechanical low back pain syndrome compared with the disc disease group. The lost-to-follow-up (unrecorded data) for the disability scores and work status variables at discharge may have influenced the results in some unpredictable way. Attrition at discharge was on the order of 50%. It should be noted, however, that at the 1-month reassessment, disability scores were obtained from 90% of the disc disease group (N = 18) and from 68% of the mechanical low back pain syndrome group (N = 15). Regarding the work status variables, attrition at 1 month was on the order of only 30%. Since the profile of the work status variables was consistent at 1 month and discharge (ie., better outcomes for mechanical low back pain syndrome compared with disc disease), it is possible that the high level of attrition at discharge did not alter the essential findings. Results suggest that patients with herniated disc have poorer shortterm outcomes than patients with mechanical low back pain syndrome. Bigos et a1 (2) have suggested that the time lost from work represent$ a primary outcome for the study of work-related back injuries. Absence from work, however, was not correlated with pain intensity and level of disability (25). Roland and Morris (25) found that self-reports of pain intensity and disability were more sensitive indicators of long-term outcome compared with absence JOSPT Volume 23 Number 3 March 1996

from work. In other words, absence from work or return-to-work could be due to factors independent of the level of disability (ie., financial/economic considerations). For these reasons, we utilized disability and physical impairment outcome measures in addition to work status. According to the scale developed by Fairbank et al (7), Oswestry scores from 41 to 60% represent "severe disability," whereas scores from 21 to 40% represent "moderate disability." The average Oswestry scores in our study at initial presentation were in the severe range for both the disc disease and mechanical low back pain syndrome groups (initial assessment vs. 1 month) (Table 2). At the time of discharge, the average Oswestry scores were below the midpoint of the moderate range for mechanical low back pain syndrome, but remained near the lower limit of "severe" for disc disease (Table 2). The use of multiple cointerventions is a common aspect of physical therapy practice. Given the somewhat unique profile of symptoms and physical impairments for patients in each group, it is unlikely that a single specific intervention would have been effective for all the patients that were treated. In addition, it was difficult to "preselect" specific interventions when there was no preexisting rationale to limit the types of treatment that are considered as current standards of care. It is of interest to compare our multiple-intervention ap proach with a limited intervention "category-specific" approach (4) and to a nonspecific "functional restoration" program (13,18). Delitto et al (4), for example, preselected patients with acute low back pain who showed symptom improvement with back extension and symptom intensification with back flexion. The treatment (extension exercise and mobilization) was specific to this "category" of patient.. Delitto et al (4) found that the treatment group had approximately a 10% improvement in the mean Owestry score from the initial assessment to the reassessment 5 days later. Long-term improvement has not yet been demonstrated using a categoryspecific approach to the treatment of low back syndrome. The similarity between the extent of improvement in disability scores for those treated with a "category-specific intervention" (4), our multiple interven tion physical therapy program (mechanical low back pain syndrome) (Figure), and a comprehensive nonspecific rehabilitation program (13), however, raises a question concerning the range of interventions that are necessary to achieve an optimal long-term outcome (ie., 1 year following onset of low back pain). Studies are currently underway in our clinic to address long-term outcomes for compensated workers who receive physical therapy treatments for low back syndrome. Various impairment-specific outcome measures have been identified in patients with low back pain (14, 33). The amount of trunk motion has been shown to increase during recovery from low back injury (13,16, 18,28). Our results support this previous finding. Motion of the spine increased significantly at 1 month and discharge compared with the initial assessment for patients with mechanical low back pain syndrome (Table 2). The improvement in forward bending for patients with mechanical low back pain syndrome (Table 2) seems to occur in parallel with the improvement in mean Oswestry scores. No significant improvement in fingertipto-floor distance, however, was observed for patients with disc disease (Table 2). While an improvement in forward bending was found only for patients with nonspecific mechanical low back pain, pain-free isometric lift capacity increased over the course of rehabilitation for both groups. At the initial evaluation, the mean pain-free static lift capacity for males and females in both groups (Table 2) was below the gender-specific norm for pain-free lift capacity (except for males in the disc group). At 1 month and discharge, however, the mean lift capacity for males and females in both groups exceeded the genderspecific norms. These findings are consistent with previous reports documenting similar improvements in patients receiving workers' compensation (18,28) and are probably related to several factors. Most patients showed some resolution of symptoms during the course of therapy that could account for increased lift capacity. In addition, the exercise programs prescribed for each patient may have been effective for reducing physical impairment even though self-perceived disability reached a plateau (Oswestry scores for patients with disc disease, Table 2). SUMMARY A physical therapy program with multiple interventions that included treatments based on the pattern of symptom provocation was provided to patients with herniated lumbar intervertebral disc and to another group of patients with mechanical low back pain syndrome. Patients with herniated lumbar intervertebral disc did not show a reduction in disability or an increase in the return-to-work rate at the time of reassessment. In contrast, patients with mechanical low back pain syndrome showed a significant decrease in disability and physical impairment and a higher frequency of return-to-work at the 1-month and discharge assessments. The types of physical therapy used in this study appear to benefit primarily patients with mechanical low back pain syndrome. Earlier intervention to reduce chronicity, treatments over a longer period of time, and longer follow-up may be necessary to establish the outcome of therapy for those with herniated disc. lospt ACKNOWLEDGMENTS We would like to express our sincere appreciation to Kathy Anderson, PT and to the clerical and support Volume 23 Number 3 March 1996 JOSIT

staff at Physical Therapy Orthopaedic Specialists, Inc., Minneapolis, MN for their assistance with the coordination and implementation of this study. REFERENCES 1. Ambrosius FM, Kremer AM, Herkner PB, DeKraker M, Bartz S: Outcome comparison of workers' compensation and noncompensation low back pain in a highly structured functional restoration program. J Orthop Sports Phys Ther 21:7-12, 1995 2. Bigos SJ, Spengler DM, Martin NA, Zeh J, Fisher L, Nachemson A, Wang MH: Back injuries in industry. A retrospective study. 11. Injury factors. Spine 11: 246-25 7, I986 3. Chaffin D: Preemployment strength testing. Updated position. J Occup Med 20:403-408, 1978 4. Delitto A, Cibulka MT, Erhard RE, Bowling RW, Tenhula ]A: Evidence for use of an extension mobilization category in acute low back syndrome: A prescriptive validation pilot study. Phys Ther 73:216-222, 1993 5. 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Wiesel SW, Feffer HL, Borenstein DG: Evaluation and outcome of low-back pain of unknown etiology. Spine 13: 679-680, 1988 35. Zeh J, Hansson T, Bigos S, Spengler D, Battie M, Wortley M: Isometric strength testing: Recommendations based on statistical analysis of the procedure. Spine 11 :43-46, 1986 36. Zylbergold RS, Piper MC: Lumbar disc disease: Comparative analysis of physical therapy treatments. Arch Phys Med Rehabil62:176-179, 1981 JOSPT Volume 23 Number 3 March 1996