OUTCOME MEASURES are becoming increasingly important

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1 1478 PROSTHETICS/ORTHOTICS/DEVICES The 2-Minute Walk Test as a Measure of Functional Improvement in Persons With Lower Limb Amputation Dina Brooks, PhD, Janet Parsons, MSc, Judith P. Hunter, MSc, Michael Devlin, MD, FRCPC, Janice Walker, MSc ABSTRACT. Brooks D, Parsons J, Hunter JP, Devlin M, Walker J. The 2-minute walk test as a measure of functional improvement in persons with lower limb amputation. Arch Phys Med Rehabil 2001;82; Objective: To determine the construct validity and responsiveness of the 2-minute walk test as a measure of function in individuals with lower extremity amputation. Design: The distances walked in 2 minutes were compared with the results on the physical functioning subscale of the Medical Outcomes Study Short-Form 36-Item Health Survey (SF-36) and the Houghton Scale. Setting: Regional amputee rehabilitation program. Patients: Retrospective data from 290 patients (mean age, 66yr) with unilateral transtibial, unilateral transfemoral, or bilateral amputations. Intervention: Repeated testing. Main Outcome Measures: Distance walked in 2 minutes, SF-36 (aggregated into physical and mental composite scores), and the Houghton score. We also examined the change in the distance before and after a rehabilitation program. Results: The distance walked in 2 minutes showed a weak correlation with the physical functioning subscale of the SF-36 (r.22, p.008) and a moderate correlation with the total Houghton score at discharge from rehabilitation (r.493, p.001). The correlation between distance walked in 2 minutes and SF-36 physical functioning subscale at follow-up was moderate (r.479, p.001). There was a significant improvement in distance walked in 2 minutes at discharge and follow-up compared with baseline (mean change standard deviation at discharge, m; at follow-up, m, p.001). Conclusion: The 2-minute walk test was responsive to change with rehabilitation in persons with lower extremity amputation. In addition, the 2-minute walk test showed adequate correlation with measures of physical functioning and prosthetic use in this population. Key Words: Amputees; Exercise test; Legs; Prostheses; Rehabilitation; Walking. From the Clinical Evaluation and Research Unit (Brooks, Parsons, Hunter, Walker), and Department of Physiatry (Devlin), West Park Healthcare Centre; St. John s Rehabilitation Hospital (Hunter); and Department of Physical Therapy (Brooks, Parsons, Hunter) and Division of Physiatry (Devlin, Walker), Faculty of Medicine, University of Toronto, Toronto, Ont, Canada. Accepted in revised form November 6, Presented in part at the Ontario Association of Amputee Care Conference, April 2000, Markham, Ont, Canada. No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the author(s) or upon any organization with which the author(s) is/are associated. Reprint requests to Dina Brooks, PhD, Clinical Evaluation and Research Unit, West Park Healthcare Centre, Rehabilitation, Complex Continuing Care and Long- Term Care, 82 Buttonwood Ave, Toronto, Ont M6M 2J5, Canada, dina.brooks@utoronto.ca /01/ $35.00/0 doi: /apmr by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation OUTCOME MEASURES are becoming increasingly important in health care. They can be used to assess the impact of a specific intervention or an overall treatment program on an individual or a group of patients, and to identify those who benefit most and least from the services provided. They are also used as productivity measures to determine treatment outcomes and to assess the cost-effectiveness and efficiency of services provided. Measures of functional performance are of particular importance in lower extremity amputees because rehabilitation goals focus on improving mobility and activity levels. 1 Walk tests can be administered as part of the assessment to monitor overall treatment effectiveness in this population. A variety of walk tests exist, including time-based tests (eg, 2-, 5-, 6-, 9- and 12-minute walk tests), fixed-distance tests (eg, 10-m, 0.5-mile, 2-km walk tests), velocity-determined walk tests (eg, self-paced walk test), and controlled pacing incremental tests (eg, incremental shuttle walk test). 2-8 Over 3 decades ago, Cooper 9 developed and validated the 12-minute performance (run) test as a guide to physical fitness in healthy young men. This test was later modified to an indoor 12- minute-walk test for the assessment of exercise tolerance in individuals with chronic bronchitis. 10 Shorter versions of this walk test, mainly the 6- and 2-minute walk tests, were also developed in similar populations. 11 These time-based tests are typically conducted in an enclosed quiet corridor. Patients are instructed to walk from end to end, covering as much ground as possible in the allotted time period. The primary outcome of interest is distance walked, but velocity can also be calculated. The 2-minute-walk test has been shown to be comparable to the 6- and 12-minute walk tests in patients with chronic respiratory disease 11 and to be correlated to measures of oxygen consumption. 12 However, many individuals with lower limb amputation in our clinical setting are unable to ambulate for 6 minutes, especially early in their rehabilitation. The 2-minute walk test has been used in our facility to measure the functional exercise capacity of persons with lower extremity amputation. An informal, unpublished, Canadian survey in 1998 of amputee programs reported that the 2-minute walk test was the second most used outcome measure, after the FIM instrument. Despite its widespread use, no studies have been performed to examine the measurement properties of the 2-minute-walk test in lower limb amputees. The purpose of this study was to examine construct validity and responsiveness of the 2-minute walk test as a measure of ambulatory mobility in patients with lower limb amputation. We chose to investigate this particular measure because it is the fastest and most efficient measure among the timed walk tests and is commonly used in lower limb amputees. In addition, studies have shown this measure to be comparable to the more established 6-minute walk test. 11,12 The construct validity of

2 WALK TEST IN PERSONS WITH LOWER LIMB AMPUTATION, Brooks 1479 Table 1: Demographics of Study Sample by Amputation Type All (n 290) TT (n 179) TF (n 60) Bilateral (n 51) Age (yr, mean SD) Men/women (%) 73/27 74/26 79/21 70/30 Length of rehabilitation (d, mean SD) Abbreviations: All, all 3 groups combined; TT, transtibial amputees; TF, transfemoral amputees; Bilateral, bilateral amputees. this test was examined by correlating the distance walked to the physical functioning subscale of Medical Outcomes Study Short-Form 36-Item Health Survey (SF-36), a generic measure of health-related quality of life (HRQOL). The responsiveness was examined by comparing the distance walked after first receiving the prosthesis to the distance walked at discharge from the program, and on follow-up 3 months later. We also correlated the distance walked in 2 minutes at discharge to the Houghton Scale score, a measure of prosthetic use. Our hypothesis was that the distance walked in 2 minutes would correlate moderately to both the physical functioning subscale of the SF-36 and the Houghton Scale and would be responsive to progress with rehabilitation. We expected the correlation to be only moderate because the physical functioning subscale is a measure of overall physical function (including the use of the upper extremity) and the Houghton Scale measures prosthetic use, whereas the 2-minute walk assesses the ability to walk. METHODS Participants Subjects consisted of patients who had completed inpatient amputee rehabilitation at our facility. A convenience sample of patients admitted between January 1997 and October 1999, and who completed a rehabilitation program, was identified. Demographic data were extracted from the program evaluation database, as were the following outcome measures: the 2-minute walk test, patient-reported prosthetic use as measured by Houghton Scale score, and HRQOL as measured by the SF-36. Inclusion criteria were that patients had unilateral or bilateral transtibial or transfemoral amputation, had been fit with prosthesis, and were able to walk. Subjects used their normal walking aids for all walk tests. A total of 290 patients with lower limb amputation were included in this study, with the greatest number consisting of subjects with unilateral transtibial amputation. The demographics of the sample are shown in table 1. As a group, the patients were elderly (age range, 21 94yr) and 212 (73%) were men. The length of rehabilitation was longest for patients with bilateral amputations and shortest for the subgroup with unilateral transtibial amputation (table 1). One hundred and ninetyfour (67%) had peripheral vascular disease and 165 (57%) had diabetes mellitus. Eighty-seven subjects (30%) had known coronary artery disease and 43 (15%) had congestive heart failure. Other comorbidities identified were stroke (n 32 [11%]), arthritis (n 12 [4%]), and chronic pulmonary disease (n 26 [9%]). We examined data from the group as a whole and from 3 subgroups defined by the types of amputations that the individuals had undergone: unilateral transtibial, unilateral transfemoral, or bilateral lower extremity. Measures The 2-minute walk test. The 2-minute walk test was administered following initial fitting of the patient s prosthesis (baseline), within 48 hours prior to discharge from hospital, and again at the 3-month outpatient follow-up clinic. Results from any interim tests were not used. Because training and learning effect is minimal after 2 practice walks, 13 the interim tests would have little effect on the results. A physical therapist or a rehabilitation assistant from the amputee-care team administered the test according to a standardized protocol. The test was administered in a quiet uncarpeted corridor where subjects were asked to walk as far as they could in 2 minutes without any further encouragement. 14 The test administrator walked behind the subject to minimize the effect of pacing. Subjects were provided with clear instructions and were allowed to rest during the 2-minute time period, if required. Distance walked was recorded in meters. SF-36 health survey. The SF-36 health survey is a subjective generic measure of HRQOL that is completed by the patient and requires between 5 to 10 minutes. 15 The instrument consists of 36 questions relating to 8 domains: physical functioning, physical role, bodily pain, general health, emotional role, social function, mental health, and vitality. These 8 subscale scores can be further aggregated into 2 composite summary scale scores. The first 4 subscales comprise the physical composite score (PCS) and the latter 4 the mental composite score (MCS). Normative data have been generated for the PCS, MCS, and the 8 subscale scores. 16 The SF-36 has not been validated in the amputee population. The SF-36 was completed within 48 hours after admission to the unit, within 48 hours prior to discharge, and at the 3-month follow-up appointment. Subscale and composite scores were calculated according to the scoring algorithms supplied by Ware et al. 16,17 Houghton Scale score. The Houghton score is a subjective measure of prosthetic use. 18,19 This questionnaire consists of 4 questions and evaluates frequency of prosthetic use in a variety of activities. The first 2 questions deal with patients overall use of their prosthesis and the remaining questions deal with prosthetic use in the environment. The total score ranges from 0 (minimum) to 12 (maximum). The Houghton score was obtained within 48 hours of discharge. Although the items have face validity, there are limited data on the reliability and validity of the total score. 20 Analysis To evaluate the strength of associations between the various measures, linear regression was performed and Pearson s correlations (r) were calculated. To test the significance of differences on repeated measures (eg, the walk distance at the 3 different time points), repeated-measures analysis of variance (ANOVA) was performed. To test differences within subgroups (ie, between men and women), independent sample t tests were performed. A p value less than.05 was considered significant. Statistical analysis was conducted using SPSS software for Windows, version 7.5. a Interpretation of the strength of correlations was based on a grading scheme used by Lacasse et al. 21 Specifically, coefficients of correlations ranging from 0 to.20 were considered a negligible correlation;.21 to.35 a weak correlation;.36 to.50 a

3 1480 WALK TEST IN PERSONS WITH LOWER LIMB AMPUTATION, Brooks Fig 1. Mean and standard error for distance walked in 2 minutes in transtibial (TT), transfemoral (TF), bilateral amputees (bilateral), and all 3 samples (all). There was a significant improvement in distance walked at discharge and follow-upcompared with baseline value (p <.001)., all;, TT;, TF; {, bilateral. moderate correlation; and greater than.50 a strong correlation. 21 RESULTS Evaluation of Change There was a significant improvement in distance walked in 2 minutes at discharge and follow-up, compared with baseline. Mean standard deviation (SD) of distance walked in 2 minutes at baseline was meters. This distance significantly increased with rehabilitation to meters and even further at follow-up to meters (repeated-measures ANOVA, p.001) (fig 1). The mean change for paired observation of distance walked in 2 minutes was meters at discharge and meters at follow-up. The pattern for improvement at discharge and further improvement at follow-up was reproducible for all 3 subpopulations (transtibial, transfemoral, bilateral amputees) (repeated-measures ANOVA, p.001) (fig 1). At baseline, transfemoral amputees scored lowest for distance walked in 2 minutes ( m). Furthermore, the distance walked in 2 minutes at baseline correlated strongly with distance walked at discharge and follow-up (r.720 and.568, respectively, p.001). Similarly, the transtibial subgroup scores for distance walked in 2 minutes at baseline was strongly correlated with distance walked at discharge and follow-up (table 2). Correlation Between the 2-Minute Walk Score and Other Measures Because of the retrospective nature of this study, many subjects had missing data at discharge or at follow-up. Subjects were included in a given analysis if they had at least 2 data points for at least 2 measures, including the 2-minute walk test. If the number of matched data points was less than 30, linear regression was not calculated. We did not correlate baseline measures of distance walked in 2 minutes and the SF-36 at admission because these were performed at different times, ie, SF-36 was administered 48 hours after admission and the walk test was performed after fitting of the prosthesis. At discharge, there was a weak correlation between the distance walked in 2 minutes and physical functioning component of the SF-36; this correlation was moderate at follow-up (table 2). However, there was no significant correlation found between the distance walked in 2 minutes and the overall PCS, either at discharge of follow-up (all p values.40). There was also no significant correlation between the distance walked in 2 minutes and the MCS, either at discharge or follow-up (all p values 0.4). In the unilateral transtibial subgroup, distance walked in 2 minutes correlated weakly with the scores from the physical functioning component of the SF-36 at discharge (r.29, p.005) and at follow-up (r.35, p.05). For the group as a whole, the correlation between the distance walked in 2 minutes and the Houghton score at discharge was moderate (n 56; r.493, p.001; table 2); similarly, for the transtibial subgroup this correlation at discharge was strong (r.53, p.02). Other Observations There was no significant correlation between length of stay (LOS) and change in distance walked in 2 minutes between baseline and discharge (r.088, p.242). This lack of correlation and significance was consistent within each of the subgroups of amputees (r.098 to.031, all p values 0.2). There was a significant difference between men and women in the distance-walked in 2 minutes (table 3). In addition, there was a greater improvement in the distance walked among men compared with women from baseline to discharge (table 3). The same pattern was observed in the transtibial subgroup, with greater distances recorded in men than women at baseline ( vs , p.02), discharge ( vs , p.001), and follow-up ( vs , p.03). The change in distance walked between baseline and discharge was also significantly greater in men ( vs , p.001). Table 2: Correlation of Distance Walked and Other Measures of Function for the Total Sample n r p 2MWD and PF of SF-36 2MWD and PF at discharge MWD and PF at follow-up MWD and 2MWD 2MWD baseline and discharge MWD baseline and follow-up MWD discharge and follow-up MWD and Houghton Scale* 2 MWD and Houghton discharge Abbreviations: 2MWD, distance walked in 2 minutes; PF, physical functioning. * Houghton Scale score was measured at discharge only.

4 WALK TEST IN PERSONS WITH LOWER LIMB AMPUTATION, Brooks 1481 Table 3: Gender Differences in Distance Walked in 2 Minutes Distance Walked in 2 Minutes Men Women p (t test) Baseline Discharge Follow-up Change: baseline to discharge NOTE: Values in mean meters SDs. There was a negative and weak correlation between age and the change in distance walked between baseline and discharge (r.289, p.001). The same pattern was observed in the transtibial subgroup, with a moderate correlation between age and the change in distance walked between baseline and discharge (r.358, p.001). For the overall sample, using stepwise regression, age, and gender moderately correlated with change in distance walked (r.369, p.001). DISCUSSION Our findings indicate that the 2-minute walk test was responsive to change during rehabilitation and recovery from lower extremity amputation. Responsiveness is the ability of a measure to assess and quantify clinically important change. 22 The large improvements in distance walked between initial, discharge, and follow-up indicates that the 2-minute walk is able to detect change in ambulatory function. The 2-minute walk test scores correlated with other measures of physical function in this population. Distance walked in 2 minutes correlated weakly at discharge and moderately at follow-up to the physical functioning subscale of the SF-36. The difference in the strength of the correlation at the 2 time frames may reflect the difference in information provided by the 2 measures and difference in sensitivity. There was also a moderate correlation between the Houghton score and the distance walked in 2 minutes at discharge. There was no significant correlation between the distance walked in 2 minutes and the PCS of the SF-36 at discharge or follow-up. A possible reason for this is that the physical functioning subscale is heavily weighted toward walking activities, while the PCS component encompasses not only domains of physical functioning, but also those of physical role, bodily pain, and general health. There was no correlation between distance walked in 2 minutes and the MCS of the SF-36, as the 2 measures reflect different constructs. Smith et al 23 examined SF-36 outcomes in a group of patients following traumatic transtibial amputation and found that the physical functioning subcategory score was different than normative data, but the other nonphysical categories were within normal range. There was also no correlation between the change in distance walked in 2 minutes and LOS because the latter may be influenced by extrinsic factors that are independent of patient status (eg, discharge planning). The 3 measures in this study provide different information on functional capacity: the SF-36 subscale examines physical functioning (including the use of the upper extremity), the Houghton Scale measures prosthetic use, and the 2-minute walk assesses the ability to walk. At present, there is no available gold standard measure of physical function that particularly evaluates ambulation ability of individuals after lower extremity amputation. We chose to commence the evaluation of the 2-minute walk test in the population of persons who had undergone amputation by correlating distance walked to both the Houghton score and SF-36 because they are the logical measures in this population. The Houghton Scale is a diseasespecific measure and has face validity. Although the SF-36 has not been validated in amputees, it is a generic measure of HRQOL that has been validated in many different populations. Furthermore, the SF-36 has been used in several studies in amputees. 20,23-25 Smith 23 and Pezzin et al 25 reported that the SF-36 subscales that are sensitive to physical health status were lower in the population of patients with lower extremity amputation than normal values, indicating that this measure reflected physical limitation in the patient group. We were able to locate only 5 studies on the measurement properties of the 2-minute walk test. 13 These studies evaluated the measure in the population of subjects with respiratory disease or in the frail elderly. Three studies addressed validity 11,12,26 ; 3 studies evaluated reliability 14,26,27 ; and 2 studies assessed responsiveness. 12,14 With respect to construct validity, Butland et al 11 and Bernstein et al 12 showed that the 2-, 6-, and 12-minute walk tests were comparable measures of exercise capacity in patients with chronic respiratory disease by showing strong correlation between distances walked at 2, 6, and 12 minutes. In addition, Bernstein 12 showed that the distance walked in 2 minutes was moderately to strongly correlated to measures of oxygen consumption. Furthermore, Upton et al 26 found that the 2-minute walk test was more discriminatory than peak expiratory flow rate in those with near normal respiratory function in pediatric patients with cystic fibrosis. With respect to responsiveness, the 2-minute walk test has been found to be less responsive than the 6-minute walk test for patients with chronic airflow limitation and/or chronic heart failure. 14 However, changes in distance walked strongly correlated with changes in maximum oxygen consumption in elderly men with chronic obstructive pulmonary disease. 12 The specific properties of the 2-minute walk test have not been examined in amputees. However, patients with unilateral or bilateral transtibial or transfemoral amputation present with serious walking disability even after completion of rehabilitation, possibly because of the greater energy cost secondary to decreased efficiency of ambulation. 28 Thus, it is valuable to compare the 2-minute walk times of persons with amputations with values reported in healthy individuals. There are 2 studies that have reported distances walked in 6 minutes in healthy subjects. 29,30 In healthy elderly (age range, 60 65yr), the distances walked in 6 minutes ranged from 494 to 631 meters, which translates to 165 to 210 meters in 2 minutes. These values are considerably higher than those observed in our sample, where the distances walked in 2 minutes ranged from meters at baseline to meters at follow-up. Caution must be used when comparing our results with those in healthy individuals because normative data are only available for the 6-minute walk test. Similarly, walking speed has been studied in healthy subjects and in subjects with transtibial amputation. 31 A normal walking velocity has been reported to be 83m/min. 31,32 In contrast, walking speed has been estimated at 45m/min for

5 1482 WALK TEST IN PERSONS WITH LOWER LIMB AMPUTATION, Brooks persons who had undergone transtibial amputation for vascular reasons and 36m/min for persons who had undergone transfemoral amputation for vascular reasons, at least 6 months after wearing a prosthesis. 33 At follow-up, the speeds we found were similar to those reported by Waters et al 33 for transtibial amputees (43.5m/min) but much lower for transfemoral amputees (19.7m/min). The difference may be the result of the timing of the measures because our subjects had worn their prosthesis for less than 6 months. Based on the comparisons of walking speeds and distance with available normative data, it is clear that individuals with transtibial or transfemoral amputation have serious limitation in ambulation. Gender and age have been reported to be independent contributors to distance walked in 6 minutes in healthy subject. 29,30 On average, the distance walked in 6 minutes was 82 to 84 meters greater in men compared with women and showed significant correlation with age (r.51, p.01). 29,30 In our study, distance walked in 2 minutes in men ranged between and meters compared with to meters in women, and the correlation between age and change in distance walked was significant. This gender and age-specific effect may be the result of differences in anthropometric measures, peripheral muscle strength, and aerobic conditioning with age and between men and women. This study included only persons with major lower extremity amputation who had completed inpatient rehabilitation. Therefore, the findings are not generalizable to the general amputee population. In addition, the design of this study did not allow us to account for the effect of maturation of the variables measured. Future studies could include variables that would not be affected by rehabilitation to ensure that the responsiveness observed was because of rehabilitation and to establish the sensitivity of this measure. Other measurement properties of the 2-minute walk, such as reliability and predictive validity, need to be established. The ability of this walk test to predict morbidity and mortality in patients with amputation needs to be examined, in light of evidence that the 6-minute walk is an excellent predictor of morbidity and mortality in patients with heart failure 34 and our observed correlation between initial score and final scores. In addition, the measurement properties of the SF-36 and the Houghton Scale need further evaluation as measures of outcome for persons with unilateral or bilateral transtibial or transfemoral amputation. CONCLUSION There is a dearth of validated outcome measures for patients with lower extremity amputation, especially for those undergoing inpatient rehabilitation. The 2-minute walk test is practical, simple, quick, and easy to administer. In this retrospective study, we found the 2-minute walk test was responsive to change with rehabilitation and was somewhat correlated with measures of physical functioning and prosthetic use in this population. Acknowledgments: We acknowledge Paul Lee, Louie Luo, and Desa Marin for their assistance with data entry and analysis. We also acknowledge the assistance of the staff on the amputee service for their role in data collection. References 1. Treweek SP, Condie ME. Three measures of functional outcome for lower limb amputees: a retrospective review. Prosthet Orthot Int 1998;22: Morice A, Smithies T. The 100 m walk: a simple and reproducible exercise test. Br J Dis Chest 1984;78: Knox AJ, Morrison JF, Muers MF. 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