Knee flexion after hospitalisation is no predictor for functional outcome one year after total knee arthroplasty

Objective: In total knee arthroplasty (TKA), range of motion has become established as an important factor. The criterion of quality is set to flexion of 90 degrees after hospitalisation. Currently, it is supposed to be a predictor for 1-year postoperative outcome. However, as this correlation has not been proven, this clinical trial was performed. Methods: A total of 182 TKA recipients were analysed retrospectively. Outcomes were assessed before surgery, after hospitalization, 6 weeks and 1 year post surgery. They included knee range of motion (ROM) to answer the main hypothesis, but also KSS, SF 36, WOMAC, EQ-5D and VAS to evaluate knee function and quality of life. The patients were divided into two groups differing in achieving 90 degrees flexion after hospitalisation and compared 6 weeks and 1 year after surgery. Results: Knee flexion differed significantly between groups from 91 to 70 degrees in the group without the aim of 90 degrees flexion after hospitalisation (E) (p < 0.001). After 6 weeks, flexion was improved to 112 degrees +/- 13 degrees (E > 90 degrees) vs. 106 degrees +/- 14 degrees (E < 90 degrees; p = 0.001). One year post surgery, knee flexion averaged 122 degrees +/- 10 degrees (E > 90 degrees) vs. 120 degrees +/- 10 degrees (E < 90 degrees) with no difference between the groups (p = 0.57) and no significant difference in all other scores concerning knee function and quality of life. Conclusion: Flexion of 90 degrees after hospitalisation is not adequate to predict medium term outcomes after TKA. There is no advantage or disadvantage regarding whether the aim of 90 degrees flexion is achieved.