Achieving normative quadriceps strength after total knee arthroplasty

Aims: This study quantified the contribution of contralateral quadriceps strength to achieving a normative quadriceps strength benchmark one year after total knee arthroplasty (TKA). We also evaluated whether achieving this benchmark was associated with patient satisfaction and function, and developed a nomogram for individualized goal setting. Methods: In this retrospective cohort study, 1,341 patients (1,475 knees) who underwent primary TKA at a single orthopaedic centre between January 2018 and December 2023, and 240 knees from 120 older adults without knee osteoarthritis (OA), were analyzed. Patients were divided into development and validation cohorts. Quadriceps strength was measured preoperatively and at one year postoperatively using a standardized protocol with a handheld dynamometer, and values were normalized to body weight. The primary outcome was achieving strength equal to or greater than tenth percentile of the reference group. Associations with one-year 2011 Knee Society Score (KSS) domains, preoperative surgical side strength, and pre- and postoperative contralateral strength were examined using generalized estimating equations. A nomogram (a graphical prediction tool) was constructed and validated to provide an individualized prediction of strength achievement. Results: At one year postoperatively, 254 knees (45.0%) achieved the tenth percentile threshold of quadriceps strength observed in older adults without knee OA. The achievement was associated with higher satisfaction (mean difference (MD) 3.12 (95% CI 1.76 to 4.48)) and functional activities scores (MD 5.82 (95% CI 3.03 to 8.61)). Additionally, this achievement was associated with preoperative surgical-side quadriceps strength (risk ratio (RR) 1.66 (95% CI 1.18 to 2.33)) and postoperative contralateral strength (RR 4.83 (95% CI 3.56 to 6.56)). The nomogram demonstrated excellent discrimination (area under the curve (AUC) 0.900 (95% CI 0.850 to 0.950) in the development cohort; AUC 0.888 (95% CI 0.847 to 0.931) in the validation cohort) and acceptable calibration. Conclusion: Achieving quadriceps strength within the distribution of older adults without knee OA following TKA is associated with clinically meaningful differences in satisfaction and functional activities. Preoperative and contralateral strength are key factors. The validated nomogram provides a practical tool for individualized rehabilitation goal setting.