In vivo kinematics of knee replacement during daily living activities: Condylar and post-cam contact assessment by three-dimensional fluoroscopy and finite element analyses.

Claudio Belvedere,Silvia Pianigiani,Fabio Catani,Alberto Leardini,Bernardo Innocenti

doi:10.1002/jor.23405

Abstract

In total knee replacement, the investigation on the exact contact patterns at the post-cam in implanted patients from real in vivo data during daily living activities is fundamental for validating implant design concepts and assessing relevant performances. This study is aimed at verifying the restoration of natural tibio-femoral condylar kinematics by investigating the post-cam engagement at different motor tasks. An innovative validated technique, combining three-dimensional fluoroscopic and finite element analyses, was applied to measure joint kinematics during daily living activities in 15 patients implanted with guided motion posterior-stabilized total knee replacement. Motion results showed physiological antero-posterior translations of the tibio-femoral condyles for every motor task. However, high variability was observed in the position of the calculated pivot point among different patients and different motor tasks, as well as in the range of post-cam engagement. Physiological tibio-femoral joint rotations and contacts at the condyles were found restored in the present knee replacement. Articular contact patterns experienced at the post-cam were found compatible with this original prosthesis design. The present study reports replaced knee kinematics also in terms of articular surface contacts, both at the condyles and, for the first time, at the post-cam. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1396-1403, 2017.

Highlights

Posterior-stabilized total knee replacement has been introduced in the mid-1970s1 as an alternative to cruciate retaining designs
Tibio-femoral contact points should be at about 2/3 of the anteroposterior length of the tibial insert, in order to increase knee flexion and to optimize the extensor mechanism. In this way a good restoration of the posterior-cruciate ligament (PCL) function is obtained by the post-cam.[24,25,27,28,29]. The former mechanism, obtained by the symmetrical and concave geometry of the polyethylene insert at the medial and lateral condyles, is likely to be the main reason for the physiological internal rotation of the tibia during knee flexion, as shown in a number of fluoroscopy data.[18,19,20,21,30]
The aims of our study were (i) to verify whether a constrained post-cam mechanism resulted in physiological knee joint kinematics; (ii) to analyze the knee flexion range at which the post-cam mechanism engages; and (iii) to investigate the influence of different motor tasks on the post-cam mechanism and on the position and translation of the tibio-femoral contact points

Summary

Introduction

Posterior-stabilized total knee replacement has been introduced in the mid-1970s1 as an alternative to cruciate retaining designs. Tibio-femoral contact points should be at about 2/3 of the anteroposterior length of the tibial insert, in order to increase knee flexion and to optimize the extensor mechanism In this way a good restoration of the PCL function is obtained by the post-cam.[24,25,27,28,29] The former mechanism, obtained by the symmetrical and concave geometry of the polyethylene insert at the medial and lateral condyles, is likely to be the main reason for the physiological internal rotation of the tibia during knee flexion, as shown in a number of fluoroscopy data.[18,19,20,21,30]. Detailed assessments of the exact contact patterns at the post-cam in implanted patients from real in vivo data during daily living activities are expected to provide fundamental information for validating implant design concepts and assessing relevant performances, but these are not yet available in the literature

Objectives

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Results

Conclusion