This September 2017 article by Hammett et al in Arthritis Care and Research found that although hip and knee replacement surgery decreased pain in did not change physical activity at 6 months after surgery

The study found physical activity among patients undergoing total knee or hip arthroplasty was not increased 6 months after the surgery despite large improvements in both pain and quality of life.

The results of this study suggests that it is important to consider more then just rehab but also strategies to actively promote changes in physical activity, such as cognitive-behavioral interventions and models for behavior change early following joint replacement.

Source: Changes in physical activity after total hip or knee arthroplasty: A systematic review and meta-analysis of 6 and 12 month outcomes – Hammett – 2017 – Arthritis Care & Research – Wiley Online Library