Changes in Physical Activity, Sleep and Knee Function After Same-Day Discharge Knee Arthroplasty

This is a prospective observational cohort study investigating postoperative recovery in patients undergoing same-day discharge knee arthroplasty (SDD-KA) for knee osteoarthritis. The primary aim is to characterize pre- to postoperative changes in physical activity, sleep quality, knee extension and flexion strength, knee range of motion, and patient-reported outcomes, and to investigate associations among these changes and their relationship with patient satisfaction.

As a prespecified secondary aim, the study will compare these outcomes between patients undergoing medial unicompartmental knee arthroplasty (UKA) and total knee arthroplasty (TKA). Patients are not randomized to UKA or TKA; the surgical procedure is determined by the treating clinical team according to established clinical indications. The study therefore represents an observational comparison of two patient cohorts undergoing different surgical procedures.

The study will include 120 patients undergoing primary SDD-KA at Turku University Hospital, Finland. The cohort will consist of 30 patients undergoing medial UKA and 90 undergoing TKA. Participants will be followed prospectively from the preoperative period through 12 months after surgery.

Physical activity and sleep will be assessed objectively using wearable accelerometers. Measurements will be performed during a two-week period before surgery, continuously from the time of surgery through 3 months postoperatively, and during a further two-week measurement period at 12 months postoperatively. Accelerometer data will be analysed at the UKK Institute for Health Promotion Research using validated algorithms. Clinical assessments will include isometric knee extension and flexion strength and active knee range of motion. Patient-reported outcomes will include knee-specific function, sleep quality, pain, health-related quality of life, and satisfaction with surgery. Assessments will be performed at predefined time points during the preoperative and postoperative follow-up period. The study is designed to provide an integrated assessment of recovery by combining objective wearable sensor-derived measures with standardized clinical assessments and patient-reported outcomes.

After completion of the 12-month follow-up, the data will be analysed by the study statistician. Baseline characteristics and outcome measures will be summarized descriptively. The primary analysis will evaluate the change in Oxford Knee Score (OKS) from baseline to 12 months in the whole cohort. As a secondary analysis, the change in OKS will be compared between the UKA and TKA groups.

Changes in outcomes over time will be assessed using linear mixed-effects models, where appropriate. Associations between physical activity variables, knee extension and flexion strength, range of motion and OKS will be assessed using models with a patient-level random effect for OKS, and with physical activity, strength, range of motion, time point and potential confounders as fixed effects. The patient-level random effect allows for handling the situations where some patients may have data missing at some time point, thus reducing the potential impact of dropout on the results. Potential confounders, including age, sex, body mass index, and ASA physical status classification, will be considered in the analyses. Multivariable regression analyses will also be used to examine associations between changes in the outcome measures.

As treatment allocation is based on clinical indication rather than randomisation, the UKA and TKA groups are expected to differ in baseline characteristics. Comparisons between the groups will therefore be adjusted for baseline characteristics, and residual confounding cannot be excluded. No adjustment for multiple comparisons will be made; analyses of secondary outcomes are considered exploratory and will be interpreted accordingly. Results will be presented with 95% confidence intervals. Statistical significance will be set at p<0.05.

Data will be collected prospectively according to a predefined study protocol. Clinical assessments and questionnaires will be performed using standardized procedures, and wearable sensor data will be collected according to the predefined measurement schedule. Data quality will be monitored through review of collected study data and checks for completeness and consistency. Missing or incomplete measurements will be documented and handled according to the prespecified statistical analysis plan.

The study will increase understanding of modifiable factors associated with recovery and satisfaction after KA. The findings may inform patient selection and support the optimisation of postoperative rehabilitation, and may help identify factors influencing recovery and surgical outcomes. Furthermore, the results may provide a foundation for designing interventions aimed at increasing postoperative mobilisation and physical activity, potentially using activity monitors to support optimal recovery, and may guide the design of future comparative studies.