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

fit with a reference anatomy in mind, specific patient anatomy will of course deviate
from this reference. Thus, the interaction of the bony anatomy and the soft tissue
morphology with the knee prosthesis during function might again lead to nonphysiological
loads and kinematics. In any case, the resulting non-physiological load
conditions and kinematics of the knee might ultimately lead to pain, bone remodeling,
high wear rates and, sometimes, implant failure or revision.
While the effects of implant mal-positioning or soft-tissue anatomy on TKA tibiofemoral
(TF) and patello-femoral contact forces were recently investigated [6], less
information is available regarding their effects on TF kinematics.
Neither clinical nor in-vitro cadaver tests allow us the versatility to test the effect of
these parameters in a systematic way. Recently, however, computational models
replicating knee function have been developed and validated, which could serve this
purpose [6,14]. Such analytical methods allow researchers to investigate the effects of
certain parameters of potential influence in a non-destructive and repeatable way. But,
these studies are mainly focused on only one TKA type or they investigate only the
effect of one mal-position configuration, mainly during walking.
The aim of this project is to evaluate the influence that implant mal-positioning and/or
ligaments insertion point positions has on tibio-femoral kinematics during a squat using
a numerical model. Although each prosthesis type in this study is represented by a
specific design, the purpose of this study is not to analyze the behavior of those specific
TKA designs but rather to determine, in general, how mal-positioning and soft-tissues
geometries can alter the TF kinematics compared to its own reference configuration.
3. MATERIALS AND METHODS
The methodology used in this work to obtain the musculoskeletal model has been
previously described by Innocenti et al. [6].
A physiological knee model was obtained from CT images and replaced with four
different TKA designs obtaining four reference replaced model. The analyzed designs
are:
1. A fixed bearing, posterior stabilized (PS) design;
2. A fixed bearing, high flexion design;
3. A hinge design;
4. A mobile bearing design .
According to previous experimental test [5], for each reference replaced model a deep
squat up to 120° with a 200 N constant hip load was simulated using a validated,
dynamic, musculoskeletal modeling system.
The following configurations were analyzed in this study for each design:
1. the reference configuration;
2. the change in location of the two collateral ligaments;
3. tibial component translations in medio-lateral and in antero-posterior direction;
4. tibial component internal-external rotation, tilting and sloping;
5. patellar heights;
6. patellar tilting.
Each replaced model was developed and analyzed using a commercial musculo-skeletal
modeling software (LifeMOD/KneeSIM 2008.1.0, LifeModeler Inc., San Clemente,
CA) [14-17].
The loaded squat was reproduced numerically, simulating an existing knee kinematics
rig [5, 18,19] in terms of geometries, constraints, inputs and outputs. The model of the