No difference in range of motion between ultracongruent and posterior stabilized design in total knee arthroplasty: a randomized controlled trial

PURPOSE: The use of an ultracongruent (UC) insert with a standard femoral component for substitution of the posterior cruciate ligament (PCL) is a bone-preserving and therefore interesting alternative to the established box and cam mechanism of posterior stabilized (PS) total knee arthroplasty (TKA). This study investigated range of motion (ROM), stability and patient-reported outcome (PRO) in UC and PS TKA. We hypothesized better knee flexion with the PS design but no difference in stability and PRO between UC and PS TKA. METHODS: A randomized controlled study was performed. One hundred and twenty-seven patients were included, 63 with an UC and 64 with a PS TKA (Columbus, Aesculap, Tuttlingen, Germany). Intraoperative stability and range of motion was measured with the use of a navigation system. Patients were assessed before surgery, 3 months and 1 year postoperatively. RESULTS: There was no difference in ROM between both groups, neither intraoperatively nor at follow-up. There was 5 mm less sagittal translation at 90° of knee flexion (p < 0.001) and more posterior femoral rollback during knee flexion in the PS TKA. Axial rotation between extension and knee flexion was reduced by both designs. UC TKA was 7 min faster (p = 0.001). At the one-year follow-up, the Knee Society Score was similar in both groups, the Oxford Knee Score demonstrated better results in the UC TKA group (p = 0.048). CONCLUSION: Increased intraoperative sagittal translation and reduced posterior femoral rollback during knee flexion of UC TKA seem to have no negative influence on short-term clinical outcome. Therefore, UC TKA seems to be a practical alternative to the established PS TKA for substitution of the PCL. This might be especially interesting for surgeons who do not always substitute the PCL. LEVEL OF EVIDENCE: I.