Objective: Postoperative knee range of motion (ROM) is among the most important factors influencing patient satisfaction after total knee arthroplasty (TKA). The purpose of this study was to clarify the time course of improvement in knee ROM up to 12 months after TKA, including intraoperative knee ROM after implantation, and to clarify a target ROM for rehabilitation after TKA.

Patients and Methods: In total, 39 knee joints in 26 patients with osteoarthritis who underwent TKA (retaining the posterior cruciate ligament) were evaluated. Goniometry was used to measure the knee range of extension and flexion preoperatively; intraoperatively; at 1 and 2 weeks after TKA; and then at 1, 3, 6, and 12 months after TKA.

Results: The postoperative extension range gradually improved up to a maximum at 6 months after TKA; there were no significant differences in the extension range between intraoperative and 6 months after TKA, intraoperative and 12 months after TKA, or 6 and 12 months after TKA. The postoperative flexion range gradually improved, with the maximum improvement observed at 3 months after TKA; there were no significant differences in the flexion range before TKA and 3, 6, and 12 months after TKA. There were no significant differences between flexion ROM measured at 3, 6, and 12 months after TKA.

Conclusions: The changes in the knee range of extension plateaued 6 months after TKA, and those in the knee range of flexion plateaued 3 months after TKA. The target range of extension for rehabilitation from 6 months to 12 months after TKA was the intraoperative range, and the target range of flexion for rehabilitation from 3 months to 12 months after TKA was the preoperative range.