Effect of continuous passive motion on restoration of knee extension after total knee arthroplasty: a systematic review and meta-analysis

Continuous passive motion (CPM) has been widely used following total knee arthroplasty (TKA) to improve postoperative recovery. However, previous systematic reviews have primarily focused on knee flexion or overall range of motion (ROM), while the effect of CPM on restoration of knee extension remains unclear.Because restoration of full knee extension is essential for gait, quadriceps function, and long-term functional recovery, yet has received considerably less attention than knee flexion in previous systematic reviews, this systematic review and meta-analysis aimed to specifically evaluate the effectiveness of CPM on postoperative knee extension and other clinically relevant outcomes after primary TKA. This systematic review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement and prospectively registered in PROSPERO (CRD420251242151). PubMed, Web of Science, Embase, the Cochrane Library, China National Knowledge Infrastructure (CNKI), and the Wanfang Database were searched from inception to May 18, 2026, without language restrictions. Randomized controlled trials comparing continuous passive motion (CPM), with or without conventional rehabilitation, versus conventional rehabilitation alone following primary total knee arthroplasty were included. The primary outcome was postoperative knee extension deficit, while secondary outcomes included knee flexion, total range of motion, visual analogue scale (VAS), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), manipulation under anesthesia (MUA), complications, and length of hospital stay. Risk of bias was assessed using the Cochrane Risk of Bias tool (RoB 1). Random-effects meta-analyses were performed to calculate pooled mean differences (MDs) and risk ratios (RRs) with 95% confidence intervals (CIs). Prespecified subgroup analyses according to follow-up duration and leave-one-out sensitivity analyses were conducted to explore temporal effects and assess the robustness of the pooled estimates(early: <6 weeks; mid-term: 6 weeks–6 months; long-term: >6 months). A total of 11 randomized controlled trials involving 1,200 patients were included. Compared with conventional rehabilitation alone, CPM did not significantly improve postoperative knee extension during the early (MD = − 0.28°, 95% CI − 0.69 to 0.12), mid-term (MD = − 0.16°, 95% CI − 0.95 to 0.64), or long-term follow-up (MD = − 0.64°, 95% CI − 1.39 to 0.12). Significant improvements in knee flexion were observed at the mid-term (MD = 1.65°, 95% CI 0.06–3.23) and long-term follow-up (MD = 3.94°, 95% CI 1.66–6.23). However, these improvements were not accompanied by clinically meaningful benefits in postoperative pain, WOMAC scores, manipulation under anesthesia, complications, or length of hospital stay. Leave-one-out sensitivity analyses confirmed the robustness of the pooled estimates despite reductions in statistical heterogeneity after exclusion of influential studies. Current evidence suggests that the routine use of continuous passive motion following uncomplicated primary total knee arthroplasty does not improve postoperative knee extension and provides limited additional clinical benefit beyond contemporary rehabilitation programmes. Although CPM may produce modest improvements in passive knee flexion, these changes do not translate into superior functional recovery or patient-reported outcomes. Rehabilitation programmes should therefore preferentially emphasize interventions that enhance quadriceps activation, neuromuscular control, and functional recovery rather than passive joint motion alone. Future high-quality randomized controlled trials using standardized CPM protocols are warranted to identify patient subgroups that may derive clinically meaningful benefit from CPM.