The six-minute walk test is an excellent predictor of functional ambulation after total knee arthroplasty. (2013)

Abstract
BACKGROUND:
The Six-minute walk (6 MW) and Timed-Up-and-Go (TUG) are short walk tests commonly used to evaluate functional recovery after total knee arthroplasty (TKA). However, little is known about walking capacity of TKA recipients over extended periods typical of everyday living and whether these short walk tests actually predict longer, more functional distances. Further, short walk tests only correlate moderately with patient-reported outcomes. The overarching aims of this study were to compare the performance of TKA recipients in an extended walk test to healthy age-matched controls and to determine the utility of this extended walk test as a research tool to evaluate longer term functional mobility in TKA recipients.
METHODS:
The mobility of 32 TKA recipients one year post-surgery and 43 healthy age-matched controls were assessed using the TUG, 6 MW and 30-minute walk (30 MW) tests. The latter test was repeated one week later. Self-reported function was measured using the WOMAC Index and a physical activity questionnaire.
RESULTS:
30 MW distance was significantly shorter amongst TKA recipients (mean 2108 m [95% CI 1837 to 2381 m]; Controls 3086 m [2981 to 3191 m], P < 0.001). Test-retest repeatability was high (ICC = 0.97, TKA; 0.96, Controls). Amongst TKA recipients, the 30 MW distance correlated strongly with the shorter tests (6 MW, r = 0.97, P < 0.001; TUG, r = -0.82, P < 0.001). Multiple regression modeling found 6 MW distance to be the only significant predictor (P < 0.001) of 30 MW distance, explaining 96% of the variability. The TUG test models were moderate predictors of WOMAC function (55%) and physical activity (36%) and were stronger predictors than 6 MW and 30 MW tests.
CONCLUSIONS:
Though TKA recipients are able to walk for 30 minutes one year post-surgery, their performance falls significantly short of age-matched norms. The 30 MW test is strongly predicted by 6 MW test performance, thus providing strong construct validity for the use of the 6 MWtest in the TKA population. Neither a short nor long walk test is a strong predictor of patient-reported function after TKA.

My comments:

The gist of this study was that the 6 minute walk test tells you 97% of what you would need to know about a 30 minute test after total knee replacement, making the latter more arduous test unnecessary. The timed up and go (TUG at 3 meters) test explained 82%. Average TUG was 7.4 seconds for the TKA group and 5.0 for controls.

The 30 minute walk test did yield some interesting data, like average speed being 1.17 meters per second (2.26 mph) in the TKA group and 1.71 meters per second (3.8 mph) in the controls (average age 65). I always like to know the mph so I can give good suggestions regarding treadmill speed goals, and 3.8 mph is moving, indicating a healthy control group. FOr the TKA group, average step length was shorter (.68 vs. .81 meters) and cadence (112 vs 124 steps/min) slower than controls. BMI of the TKA group was 30.8 and controls were 23.6, which researchers  said explained some but not all of the difference.

I like this study; I think a good take home message for patients is that if you want normal health after a total knee replacement, you want to walk normally, and normal is upwards of  3.5 to 4 mph. Also, typical physical therapy programs are not getting people there.  More emphasis on recovery should be directed at not losing muscle in first place with early electric muscle stimulation, higher intensity exercise, and regular monitoring of progress with functional tests including but not limited to the TUG and 6 minute walk test.