BACKGROUND: To determine the effectiveness and therapeutic validity of physiotherapeutic exercise after total and unicompartmental knee arthroplasty for osteoarthritis. It was hypothesized that interventions of high therapeutic validity result in superior functional recovery after total and unicompartmental knee arthroplasty versus interventions of low therapeutic validity. METHODS: A systematic review incorporating a comprehensive database search of five major databases relevant to the topic was conducted. Randomized controlled trials were reviewed if they included studies that compared postoperative physiotherapeutic exercise with usual care or compared two types of postoperative physiotherapeutic interventions. All included studies were assessed for risk of bias (using the Cochrane Collaboration's tool) and therapeutic validity (using the Consensus on Therapeutic Exercise Training scale). The characteristics of the included articles and their results on joint and muscle function, functional performance, and participation were extracted. RESULTS: Of the 4343 unique records retrieved, 37 articles were included. Six of them showed good therapeutic validity, suggesting low therapeutic validity in 31 studies. Three articles showed a low risk of bias, 15 studies scored some concerns for risk of bias and 19 studies scored high risk of bias. Only one article scored well on both methodological quality and therapeutic validity. CONCLUSION: Due to heterogeneity of outcome measures and length of follow-up, as well as limited reporting of details of the physiotherapeutic exercises and control interventions, no clear evidence was found on effectiveness of physiotherapeutic exercises after total and unicompartmental knee arthroplasty. Homogeneity in intervention characteristics and outcome measures would enhance comparability of clinical outcomes between trials. Future studies should incorporate similar methodological approaches and outcome measures. Researchers are encouraged to use the Consensus on Therapeutic Exercise Training scale as a template to prevent insufficient reporting.