The Six-Minute Walk Test Predicts Ambulation After TKA
The Six-Minute Walk Test Predicts Ambulation After TKA
Maximizing functional mobility is a key goal of rehabilitation after total knee arthroplasty (TKA) surgery. The Timed-Up-and-Go (TUG) and Six-minute walk (6MW) tests are commonly used to evaluate functional recovery after TKA as they are simple to administer and reliable. However, for research demonstrating long-term functional recovery after TKA an extended walk test may be more useful as an outcome measure for several reasons. Firstly, little is known about walking ability beyond six minutes amongst TKA recipients. At 12 months or more after surgery, when functional performance is considered close to optimum, TKA recipients may wish to walk for longer duration for fitness or occupational needs. As such, a longer walk test can provide insight into ambulatory capacity over a more functional, everyday duration, and therefore, have greater face validity. Secondly, by extension, if a longer test approximates true functional requirements more than a shorter test, it may have a stronger correlation with self-reported behaviors than that associated with the shorter walk tests. The TUG and 6MW tests have been shown to have only moderate correlations at best with measures of self-reported function after TKA and with physical activity in people with end-stage knee osteoarthritis, suggesting that self-reported function tools and timed mobility tests measure different aspects of function. Consequently, both forms of assessment are considered necessary post-surgery. We contend, therefore, if an extended mobility test has greater correlation with perceived function simply because it may be more 'functional', then the extended walk could be a close proxy for self-reported function (or vice versa). Thirdly, a longer walk test may be useful in discriminating between individuals because it is likely that not every individual can maintain the fast paced walking achieved in the 6MW test over a longer period. It is possible that individuals who appear comparable on a short duration walk test exhibit fatigue and differences in walking endurance beyond six minutes of walking.
The use of extended walk tests has been investigated in other populations. In a study of the two-, six-and 12-minute walk tests in patients following stroke, the 12-minute walk test was observed to be the most responsive to change. Further, despite high correlation between the three tests, the two-minute assessment was reported to overestimate 6 and 12 minute walking distances. The authors suggested the overestimation may be due to fatigue during the longer tests. In another study investigating patients with stable chronic airflow obstruction, a 12-minute walk test was also found to be highly correlated to six-minute and two-minute walk tests. Variance of the 12-minute walk test was greater than the shorter walk tests, suggesting that the longer test was perhaps more discriminating. However, as the shorter walk tests were easier for both the patient and researcher, the authors recommended the six-minute walk as a fair compromise. Compared to other patient populations, TKA recipients may be affected by different factors which limit walking capacity, such as residual knee pain and reduced muscle strength. As such, it cannot be assumed that the results of these studies can be generalized to the TKA population.
To date, there has been no examination of the utility of a walking test beyond six minutes in the TKA population. The overarching aim of this study was to determine the utility of an extended walk test as a research tool to evaluate longer-term functional mobility in TKA recipients. The specific aims of the study were multiple: 1) to assess the performance and repeatability of the extended test in TKA recipients one year after surgery and in healthy age-matched controls; 2) to examine the correlations between the extended walk test and both the TUG and 6MW tests amongst the TKA cohort; 3) to determine the predictors of performance of the extended walk test amongst the TKA cohort; and finally, 4) to examine which of the walk tests best predicts self-reported function and physical activity. The main hypotheses to be addressed were that: TKA recipients one year post-surgery will perform significantly worse than age-matched healthy controls in an extended walk test; the shorter walk tests will not predict performance in the longer walk test, and; the longer walk test will be a stronger predictor of self-reported function and physical activity than the shorter walk tests.
Background
Maximizing functional mobility is a key goal of rehabilitation after total knee arthroplasty (TKA) surgery. The Timed-Up-and-Go (TUG) and Six-minute walk (6MW) tests are commonly used to evaluate functional recovery after TKA as they are simple to administer and reliable. However, for research demonstrating long-term functional recovery after TKA an extended walk test may be more useful as an outcome measure for several reasons. Firstly, little is known about walking ability beyond six minutes amongst TKA recipients. At 12 months or more after surgery, when functional performance is considered close to optimum, TKA recipients may wish to walk for longer duration for fitness or occupational needs. As such, a longer walk test can provide insight into ambulatory capacity over a more functional, everyday duration, and therefore, have greater face validity. Secondly, by extension, if a longer test approximates true functional requirements more than a shorter test, it may have a stronger correlation with self-reported behaviors than that associated with the shorter walk tests. The TUG and 6MW tests have been shown to have only moderate correlations at best with measures of self-reported function after TKA and with physical activity in people with end-stage knee osteoarthritis, suggesting that self-reported function tools and timed mobility tests measure different aspects of function. Consequently, both forms of assessment are considered necessary post-surgery. We contend, therefore, if an extended mobility test has greater correlation with perceived function simply because it may be more 'functional', then the extended walk could be a close proxy for self-reported function (or vice versa). Thirdly, a longer walk test may be useful in discriminating between individuals because it is likely that not every individual can maintain the fast paced walking achieved in the 6MW test over a longer period. It is possible that individuals who appear comparable on a short duration walk test exhibit fatigue and differences in walking endurance beyond six minutes of walking.
The use of extended walk tests has been investigated in other populations. In a study of the two-, six-and 12-minute walk tests in patients following stroke, the 12-minute walk test was observed to be the most responsive to change. Further, despite high correlation between the three tests, the two-minute assessment was reported to overestimate 6 and 12 minute walking distances. The authors suggested the overestimation may be due to fatigue during the longer tests. In another study investigating patients with stable chronic airflow obstruction, a 12-minute walk test was also found to be highly correlated to six-minute and two-minute walk tests. Variance of the 12-minute walk test was greater than the shorter walk tests, suggesting that the longer test was perhaps more discriminating. However, as the shorter walk tests were easier for both the patient and researcher, the authors recommended the six-minute walk as a fair compromise. Compared to other patient populations, TKA recipients may be affected by different factors which limit walking capacity, such as residual knee pain and reduced muscle strength. As such, it cannot be assumed that the results of these studies can be generalized to the TKA population.
To date, there has been no examination of the utility of a walking test beyond six minutes in the TKA population. The overarching aim of this study was to determine the utility of an extended walk test as a research tool to evaluate longer-term functional mobility in TKA recipients. The specific aims of the study were multiple: 1) to assess the performance and repeatability of the extended test in TKA recipients one year after surgery and in healthy age-matched controls; 2) to examine the correlations between the extended walk test and both the TUG and 6MW tests amongst the TKA cohort; 3) to determine the predictors of performance of the extended walk test amongst the TKA cohort; and finally, 4) to examine which of the walk tests best predicts self-reported function and physical activity. The main hypotheses to be addressed were that: TKA recipients one year post-surgery will perform significantly worse than age-matched healthy controls in an extended walk test; the shorter walk tests will not predict performance in the longer walk test, and; the longer walk test will be a stronger predictor of self-reported function and physical activity than the shorter walk tests.
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