Changes in knee outcome measures following later-stage exercise interventions implemented ≤ 12 weeks vs. > 12 weeks after total knee arthroplasty: a systematic review and meta-analysis.

backgroundLater-stage exercise interventions refer to rehabilitation exercises implemented after the initial healing phase. Following total knee arthroplasty (TKA), patients generally begin these high-intensity exercises at the 2-month mark. Nevertheless, the duration of these exercise programs varies across studies, and the extent to which later-stage exercises contribute to improvements in the knee outcome measures over time remains unclear. This study aims to systematically evaluate the changes in the knee outcome measures following later-stage exercise interventions implemented at ≤ 12 weeks versus > 12 weeks after TKA.

methodsThe PubMed, Scopus, and Web of Science databases were searched through May 2025 to identify the randomized controlled trials evaluating the effects of later-stage exercise interventions on the knee outcome measures. The certainty of evidence was assessed using the Grading of Recommendations Assessment, Development, and Evaluation approach. Additionally, the completeness of the intervention descriptions was evaluated using the Template for Intervention Description and Replication checklist. A subgroup analysis was conducted to compare the outcomes of interventions lasting ≤ 12 weeks with those lasting > 12 weeks. Moreover, the minimal detectable change (MDC) values were referenced to interpret the clinical relevance of the observed changes.

resultsFifteen studies involving 1,160 TKA patients were included. Across all studies, the sit-to-stand performance was observed to be enhanced by 2.61 s or 2.7 repetitions; the stair climbing duration decreased by 3.35 s; the knee flexor strength increased by 3.36 kg-force; and the knee extension angle reduced by 3.96°. For interventions ≤ 12 weeks, the timed up-and-go improved by 2.78 s. For interventions > 12 weeks, the knee extensor strength increased by 15.59 kg-force, and the knee flexion angle improved by 14.40°. The certainty of evidence ranged from low to moderate, and the intervention descriptions demonstrated moderate completeness.

conclusionMany observed changes in the knee outcome measures exceeded the MDC thresholds, indicating clinically meaningful benefits from later-stage exercise interventions post-TKA. The interventions implemented at ≤ 12 weeks primarily improved the functional performance, whereas those lasting > 12 weeks resulted in greater gains in the muscle strength and joint flexibility. Stronger evidence and more detailed intervention descriptions are needed to better integrate these findings into rehabilitation practice.