Abstract
Introduction
Following primary total knee arthroplasty (TKA), patients experience pain relief and report improved physical function and activity. However, there is paucity of evidence that patients are truly more active in daily life after TKA. The aims of this study were: 1) to prospectively measure physical activity with a wearable motion sensor before and after TKA; 2) to compare patient-reported levels of physical activity with objectively assessed levels of physical activity before and after TKA; 3) to investigate whether differences in physical activity after TKA are related to levels of physical function.
Methods
22 patients (age=66.6 ±9.3yrs; m/f= 12/11; BMI= 30.6 ±6.1) undergoing primary TKA (Vanguard, ZimmerBiomet), were measured preoperatively and 1–3 years postoperatively. Patient-reported outcome measures (PROMs) included KOOS-PS and SQUASH for assessment of perceived physical function and activity resp. Physical activity was assessed during 4 consecutive days in patients” home environments while wearing an accelerometer-based activity monitor (AM) at the thigh. All data were analysed using semi-automated algorithms in Matlab. AM-derived parameters included walking time (s), sitting time (s) standing time (s), sit-to-stand transfers, step count, walking bouts and walking cadence (steps/min). Objective physical function was assessed by motion analysis of gait, sit-to-stand (STS) transfers and block step-up (BS) transfers using a single inertial measurement unit (IMU) worn at the pelvis. IMU-based motion analysis was only performed postoperatively. Statistical comparisons were performed with SPSS and a per-protocol analysis was applied to present the results at follow-up.
Results
Data were available for 17 of 22 patients at follow-up. PROMs demonstrated significant improvement of perceived physical function (KOOS-PS=68±21 vs. 34±26; p<0.001) and physical activity (SQUASH=2584 ±1945 vs. 3038 ±2228; p<0.001) following TKA. AM-based parameters of physical activity demonstrated no significant differences between pre- and postoperative quantitative outcomes. Only the qualitative outcome of walking cadence significantly changed after TKA (81.41 ±10.86 (steps/min) vs. 94.24 ±7.20 resp.; p<0.001). There were moderate correlations between self-reported and objectively assessed levels of physical activity after TKA (Pearson”s r=0.36–0.43; p<0.05). Outcomes of physical activity after TKA were moderately correlated to IMU-based functional outcome measures (Pearson”s r = 0.31 – 0.48; p<0.05).
Conclusion
1–3 years after TKA, patients demonstrate improved function. However, the self-perceived higher activity level (+18%) after TKA is not supported by any objective data obtained by wearable motion sensors such as steps, transfers or time-on-feet. This may have implications for general health and requires further investigation into patient communication, expectation management or motivational intervention.
