Both the average daily step count and MVPA time significantly increased at 6 months after TKA compared with the preoperative levels, but the LPA time did not differ significantly between the pre- and postoperative time points (Table 2).
Table 2
Physical activity assessed preoperatively and 6 months postoperatively
Assessments | Preoperative | 6 months postoperative | p-value | Effect size |
Average daily step count (steps/day) | 4717.7 ± 2533.1 | 5353.8 ± 2706.9 | < 0.001 | 0.433 |
Time spent in LPA (min) | 49.4 ± 25.1 | 51.6 ± 23.8 | 0.213 | 0.160 |
Time spent in MVPA (min) | 4.5 ± 5.6 | 7.9 ± 7.9 | < 0.001 | 0.665 |
LPA, light-intensity physical activity; MVPA, moderate-to-vigorous-intensity physical activity
Physical activity was analyzed using Wilcoxon signed-rank test
Note
Data are expressed as means ± standard deviations. Statistically significant p values are shown in bold font. Effect size: < 0.1 = trivial effect, 0.1–0.3 = small effect, 0.3–0.5 = medium effect; and > 0.5 = large effect
Correlation analysis between physical activity at 6 months after TKA and knee function, the TUG test time, and physical activity before TKA showed that physical activity at 6 months after TKA was significantly correlated with several parameters (Tables 3–5).
Table 3
Spearman correlation coefficients for associations between step count 6 months postoperatively and measured preoperatively variables
| Average daily step count 6 months postoperatively |
Variables | Correlation coefficient | p-value |
Knee-flexion ROM operated side preoperatively | 0.238 | 0.020 |
Knee-flexion ROM contralateral side preoperatively | 0.286 | 0.005 |
Knee-extension ROM operated side preoperatively | 0.135 | 0.193 |
Knee-extension ROM contralateral side preoperatively | 0.210 | 0.041 |
Knee-extension muscle strength operated side preoperatively | 0.312 | 0.002 |
Knee-extension muscle strength contralateral side preoperatively | 0.323 | 0.001 |
Knee pain, VAS operated side preoperatively | -0.036 | 0.728 |
Knee pain, VAS contralateral side preoperatively | 0.071 | 0.494 |
TUG test time preoperatively | -0.344 | 0.001 |
Average daily step count preoperatively | 0.845 | < 0.001 |
ROM, range-of-motion; VAS, visual analog scale; TUG, Timed Up-and-Go
Note
Statistically significant p values are shown in bold font
Table 4
Spearman correlation coefficients for associations between LPA time 6 months postoperatively and measured preoperatively variables
| Time spent in LPA 6 months postoperatively |
Variables | Correlation coefficient | p-value |
Knee-flexion ROM operated side preoperatively | 0.224 | 0.029 |
Knee-flexion ROM contralateral side preoperatively | 0.260 | 0.011 |
Knee-extension ROM operated side preoperatively | 0.172 | 0.096 |
Knee-extension ROM contralateral side preoperatively | 0.182 | 0.077 |
Knee-extension muscle strength operated side preoperatively | 0.273 | 0.007 |
Knee-extension muscle strength contralateral side preoperatively | 0.238 | 0.020 |
Knee pain, VAS operated side preoperatively | 0.004 | 0.970 |
Knee pain, VAS contralateral side preoperatively | 0.189 | 0.066 |
TUG test time preoperatively | -0.247 | 0.017 |
Time spent in LPA preoperatively | 0.842 | < 0.001 |
ROM, range-of-motion; VAS, visual analog scale; TUG, Timed Up-and-Go; LPA, light-intensity physical activity
Note
Statistically significant p values are shown in bold font
Table 5
Spearman correlation coefficients for associations between MVPA time 6 months postoperatively and measured preoperatively variables
| Time spent in MVPA 6 months postoperatively |
Variables | Correlation coefficient | p-value |
Knee-flexion ROM operated side preoperatively | 0.214 | 0.037 |
Knee-flexion ROM contralateral side preoperatively | 0.245 | 0.016 |
Knee-extension ROM operated side preoperatively | 0.099 | 0.340 |
Knee-extension ROM contralateral side preoperatively | 0.170 | 0.099 |
Knee-extension muscle strength operated side preoperatively | 0.295 | 0.004 |
Knee-extension muscle strength contralateral side preoperatively | 0.356 | < 0.001 |
Knee pain, VAS operated side preoperatively | -0.144 | 0.164 |
Knee pain, VAS contralateral side preoperatively | -0.090 | 0.384 |
TUG test time preoperatively | -0.396 | < 0.001 |
Time spent in MVPA preoperatively | 0.763 | < 0.001 |
ROM, range-of-motion; VAS, visual analog scale; TUG, Timed Up-and-Go; MVPA, moderate-to-vigorous-intensity physical activity
Note
Statistically significant p values are shown in bold font
A hierarchical multiple linear regression analysis, after adjusting for age, sex, BMI, and presence of DM, revealed that a higher average daily step count at 6 months after TKA was significantly associated with greater preoperative knee-extension muscle strength on the operated side (β = 0.155; p = 0.028) and a higher preoperative average daily step count (β = 0.834; p < 0.001) (Table 6). Similarly, longer LPA time at 6 months after TKA was significantly associated with greater preoperative knee-extension muscle strength on the operated side (β = 0.151; p = 0.037) and longer preoperative LPA time (β = 0.818; p < 0.001) (Table 6). In addition, longer MVPA time at 6 months after TKA was significantly associated with longer preoperative MVPA time (β = 0.723; p < 0.001) (Table 6).
Table 6
Hierarchical multiple regression analysis of factors associated with physical activity 6 months postoperatively
Variables | Step 1 | | | | Step 2 | | |
| B | β | p-value | | B | β | p-value |
Average daily step count | | | | | | | |
Intercept | 25206.5 | | < 0.001 | | 380.5 | | 0.917 |
Age | -210.6 | -0.511 | < 0.001 | | 4.2 | 0.010 | 0.898 |
Sex (0: men; 1: women) | 801.6 | 0.111 | 0.268 | | 869.2 | 0.121 | 0.072 |
BMI | -182.6 | -0.255 | 0.015 | | -63.3 | -0.088 | 0.197 |
DM (0: without DM; 1: with DM) | -1205.8 | -0.203 | 0.049 | | 202.2 | 0.034 | 0.610 |
Knee-extension muscle strength operated side preoperatively | | | | | 1218.2 | 0.155 | 0.028 |
Average daily step count preoperatively | | | | | 0.9 | 0.834 | < 0.001 |
Adjusted R2 | 0.317 | | 0.739 |
Time spent in LPA | | | | | | | |
Intercept | 13030.3 | | < 0.001 | | 860.6 | | 0.657 |
Age | -105.6 | -0.483 | < 0.001 | | -3.4 | -0.016 | 0.841 |
Sex (0: men; 1: women) | 546.2 | 0.143 | 0.161 | | 488.0 | 0.128 | 0.062 |
BMI | -95.5 | -0.252 | 0.018 | | -37.2 | -0.098 | 0.162 |
DM (0: without DM; 1: with DM) | -631.4 | -0.200 | 0.055 | | 137.9 | 0.044 | 0.521 |
Knee-extension muscle strength operated side preoperatively | | | | | 628.2 | 0.151 | 0.037 |
Time spent in LPA preoperatively | | | | | 0.8 | 0.818 | < 0.001 |
Adjusted R2 | 0.297 | | 0.727 |
Time spent in MVPA | | | | | | | |
Intercept | 3503.0 | | < 0.001 | | 898.7 | | 0.136 |
Age | -32.8 | -0.459 | < 0.001 | | -5.9 | -0.082 | 0.353 |
Sex (0: men; 1: women) | 78.2 | 0.063 | 0.561 | | 89.5 | 0.072 | 0.357 |
BMI | -24.8 | -0.199 | 0.074 | | -13.3 | -0.107 | 0.187 |
DM (0: without DM; 1: with DM) | -149.6 | -0.145 | 0.188 | | -25.5 | -0.025 | 0.759 |
Time spent in MVPA preoperatively | | | | | 1.0 | 0.723 | < 0.001 |
Adjusted R2 | 0.209 | | 0.589 |
BMI, body mass index; DM, diabetes mellitus; LPA, light-intensity physical activity; MVPA, moderate-to-vigorous-intensity physical activity |
Note: B is the partial regression coefficient and β is the standardized partial regression coefficient. Statistically significant p values are shown in bold font
The variance inflation factor was < 10, indicating that no collinearity existed among the variables and that none of the significant relationships were inflated by correlations between independent variables [32]. Residual plots indicated a random distribution pattern. Independence was observed among the residual errors of average daily step count, time spent in LPA, and time spent in MVPA at 6 months after TKA (Durbin–Watson statistic: 2.059, 1.932, and 2.195, respectively). These findings confirmed the validity of the multivariate regression analysis results.