ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

VALIDATION OF SPECIMEN SPECIFIC ROBOTICALLY
CALIBRATED KNEE VIRTUAL MODELS USING ROBOT
EXPERIMENTS
E. Siggelkow 1 , I. Sauerberg 1 , F. Benazzo 2 , M. Bandi 3
1 ABSTRACT
Passive kinematics and kinetics of the human knee joint are dependent on the topology
of the component joint surfaces as well as the properties of the passive soft tissue
structures including ligaments and the capsule. Recent explicit computer models have
been used for prediction of knee joint kinematics based on experimental investigations.
However, most of these models replicated experimental knee simulators, which
simulated soft tissue structures as springs or elastomeric structures. New generations of
experimental setups deploy industrial robots for measuring kinematics and kinetics in
six degrees of freedom and directly assess the contribution of soft tissue structures.
Based on these experimental data specimen specific soft tissue properties can be
incorporated into computer models, which leads therefore to more realistic predictions
of kinematics. Final evidence of the quality of the kinematic prediction of computer
models is given by validating those models against experimental data derived from
robot experiments.
The objective of this study was to develop and validate specimen specific computer
models suitable for predicting knee joint kinematics for laxity tests of the reconstructed
knee.
The method presented here for modeling knee joints is generally well suited for
analyzing the behavior of total knee replacements (TKR) under laxity loading
conditions. The small averaged root mean square deviation (RMSD) values for varusvalgus
(VV) rotation allow for accurate virtual assessment of ligament balancing after
virtual TKR which is the basis for all other laxity tests analyzed with the models.
2 INTRODUCTION
The application of finite element (FE) models is a common method for supporting
design of prostheses [1] through prediction of function. By enabling exploration of
kinematics and kinetics specific to the joint of a single specimen, reflecting both joint
surface topology and soft tissue properties, this method allows interrogation of different
design parameters within a short time compared to experimental evaluation. Specimen
specific joint laxity and its influence on kinematics and kinetics following TKR can be
analyzed.
Explicit dynamic FE analyses, validated against experimental investigations, have
recently been used to predict TKR kinematics and contact mechanics during dynamic
loading scenarios [2,3,4,5]. The quality of predictions made by those models is highly
1
Research Engineer, Joint Biomechanics Research, Zimmer GmbH, 8404 Winterthur, Switzerland
2
Professor, Clinica Ortopedica e Traumatologica, University of Pavia, Fondazione IRCCS, Policlinico
San Matteo, Pavia, Italy
3
Manager, Joint Biomechanics Research, Zimmer GmbH, 8404 Winterthur, Switzerland