Geometric variable designs of cam/post mechanisms influence the kinematics of knee implants
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Reproducing the femoral rollback through specially designed mechanism in knee implants is required to achieve full knee function in total knee arthroplasty. Most contemporary implants use cam/post mechanism to replace the function of Posterior Cruciate Ligament. This study was aimed to determine the most appropriate cam and post designs to produce normal femoral rollback of the knee.
Three different cams (triangle, ellipse, and circle) and three different posts (straight, convex, concave) geometries were considered in this study and were analysed using kinematic analyses. Femoral rollback did not occur until reaching 50° of knee flexion. Beyond this angle, two of the nine combinations demonstrate poor knee flexion and were eliminated from the study.
The combination of circle cam with concave post, straight post and convex post showed 15.6, 15.9 and 16.1 mm posterior translation of the femur, respectively. The use of ellipse cam with convex post and straight post demonstrated a 15.3 and 14.9 mm femoral rollback, whilst the combination of triangle cam with convex post and straight post showed 16.1 and 15.8 mm femoral rollback, respectively.
The present study demonstrates that the use of circle cam and convex post created the best femoral rollback effect which in turn produces the highest amount of knee flexion. The findings of the study suggest that if the design is applied for knee implants, superior knee flexion may be possible for future patients.
Level of evidence
KeywordsOrthopaedics Implant designing Total knee arthroplasty
This study has been supported by eScience Fund research grant from the Ministry of Science, Technology and Innovation Malaysia and FRGS research grant from the Ministry of Higher Education Malaysia. Authors also acknowledge financial support from Universiti Teknologi Malaysia RU Grant. More than one of the authors of this paper is supported by the University of Malaya HIR-MoE (Reference number - UM.C/625/1/HIR/ MOHE/MED/04, Account number - E000003-20001) research grant initiative. All authors have no competing interests and the nature of work did not require any ethical approval.