Mobile-bearing total knee arthroplasty: More rotation is evident during more demanding tasks

• Most in vivo studies on axial knee rotation utilized gait or knee bending tasks.
• Some reports showed few but significant more rotation in mobile-bearing variants of TKA.
• We studied rotation in mobile- and fixed-bearing TKA patients, while performing a sit-to-walk task with and without turning steps.
• The mobile-bearing group showed significant more rotation.
• The study illustrates how higher demanding task loads could be helpful in exploring the geometric constraints of TKA variants.

BackgroundSome reports showed few but significant more axial femorotibial rotation in favor of mobile-bearing (MB) versus fixed-bearing (FB) total knee arthroplasty (TKA), mostly during knee bend fluoroscopic studies. The goal of the current study was to submit MB and FB groups of TKA patients to a turning activity, in which additional rotation was to be expected.MethodsTwo consecutive cohorts of patients after TKA (10 FB and 11 MB knees in a total of 18 patients) were assessed using motion analysis five year postoperatively, while performing gait and sit-to-walk (STW) movements with and without turning steps.ResultsMean range of rotation in the FB group increased from 9.7° during gait, to 11.7° during STW straight, and to 14.3° during STW turning. Mean range of rotation in the MB group increased from 13.4° during gait to 21.0° during STW straight, and stayed at 21.1° during STW turning.ConclusionsToo many uncontrolled variables in the current study hinder a meaningful discrimination of MB from FB TKA rotation. However, the study does illustrate how more demanding task loads could be helpful in exploring the geometric constraints of TKA variants.Level of EvidenceLevel III, therapeutic study.