Abstract
Introduction: Recently, many different mobile bearing TKA designs are being implanted throughout the world. Also,fluoroscopy has been used to evaluate variousTKA under in vivo conditions to determine the kinematics. The objective of this study was to utilize a randomized prospective study to evaluate the kinematic patterns, for Japanese subjects implanted with two different mobile bearing TKA.
Methods: Twenty Japanese subjects were entered into a prospective study. Ten subjects were implanted with a mobile bearing TKA, which is free to rotate around the longitudinal axis of the tibia (MB1). The other ten subjects were implanted with a mobile bearing TKA that allows for unrestricted translation and rotation (MB2). Femorotibial contact positions were analyzed using video fluoroscopy. Each subject, while under fluoroscopic surveillance, was asked to perform gait. Video images were downloaded to a workstation computer and analyzed at varying degrees of gait stance. Femorotibial contact paths for the medial and lateral condyles were then determined using a computer automated model-fitting technique. Femorotibial contact anterior to the tibial midline in the sagittal plane was denoted as positive and contact posterior was denoted as negative.
Results: During gait, on average, subjects implanted with MB1 experienced minimal A/P translation of either condyle. Also, all subjects having MB1 experienced similar motion patterns throughout the stance phase of gait. Axial rotation was evident in these subjects, as one condyle would move in the anterior direction, a similar amount to the other condyle moving posterior. On average, subjects implanted with MB2 experienced both translation and rotation. The amount of translation for subjects with MB2 was greater than subjects with MB1. The kinematic patterns for subjects having MB2 were also more variable than subjects having MB1. Axial rotation was also evident for subjects having MB1.
Discussion: This study has shown that the kinematic patterns for subjects having two different mobile bearing TKA designs differed considerably. Subjects implanted with a mobile bearing TKA that only allows for free rotation, experienced minimal A/P motion and significant axial rotation (MB1). Subjects implanted with a mobile bearing TKA that allows for free translation and rotation did experience both types of motions (MB2). There was minimal variability in the kinematic patterns for subjects implanted with MB1, while subjects implanted with MB2 experienced more variable kinematic patterns.
The abstracts were prepared by Nico Verdonschot. Correspondence should be addressed to him at Orthopaedic Research Laboratory, University Medical Centre, PO Box 9101, 6500 HB Nijmegen, The Netherlands.
