Mid-term clinical outcomes and isokinetic performance after primary total knee arthroplasty within a modified ERAS protocol: a single-blinded randomized controlled trial

Background Persistent muscular deficits are a major contributor to functional limitations following total knee arthroplasty (TKA). While Enhanced Recovery After Surgery (ERAS) protocols are increasingly adopted to improve postoperative outcomes, their influence on mid-term objective muscle strength recovery remains insufficiently defined. This study aimed first, to determine whether a modified ERAS protocol enhances mid-term recovery of knee muscle strength after primary TKA and second, compare associated clinical outcomes using validated functional and patient-reported measures. Methods The study received ethical approval from the Ethics Committee of the University of Regensburg, Germany (Reference No. 19-1470-101 on 31 July 2019) and was conducted in accordance with the principles of the Declaration of Helsinki. In this prospective, single-blinded randomized controlled trial, 58 patients undergoing primary TKA were assigned to either a modified ERAS protocol ( n = 31) or conventional perioperative care ( n = 27). Assessments were conducted at 5 days, 4 weeks, 3 months, 6 months, and 12 months postoperatively. Isokinetic muscle strength - including peak torque (Nm), total work (J), and power (W) - was measured using the Biodex ® System 3 Dynamometer. Clinical outcomes were evaluated using the Numeric Rating Scale (NRS) for pain, Patient-Reported Outcome Measures (PROMs), and the Knee injury and Osteoarthritis Outcome Score (KOOS). Results At 5 days postoperatively, the ERAS group demonstrated significantly higher isokinetic muscle strength and improved active knee flexion compared to the conventional group ( p < 0.05). These early differences decreased over time, with no significant differences observed between groups at 3, 6, or 12 months. Both groups demonstrated excellent mid-term outcomes, with similarly high patient satisfaction and comparable PROMs and KOOS scores at the one-year follow-up. Conclusion The modified ERAS protocol led to significantly improved early postoperative recovery of knee muscle strength without adversely affecting short- or mid-term outcomes. Although isokinetic and clinical measures aligned across groups over time, the ERAS approach appears to be a safe and effective strategy for enhancing early functional recovery and overall patient experience following primary TKA.