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Introduction
•Musculo-skeletal (MS) models are emerging as potential tools
for the aid in orthopedic interventions, including Total Knee
Arthroplasty (TKA).
•Recently, we presented and validated a subject-specific MS
model of TKA [1] that incorporates realistic contact, ligament
restraint and muscle activation.
•Knee joint stability has previously not been evaluated.
•Establishing realistic model predictions of kinematics as well
as joint stability is an essential step towards clinical use.
Objective
The aim of this study was to evaluate the model-predicted knee
joint stability, as obtained from simulations of knee joint laxity.
Material and Methods
•Model. A previously validated model of TKA [1]. Only femur,
tibia and patella are included. The femur was constrained in
all directions except flexion-extension, which was being
driven. Tibia flexion-extension was constrained, leaving 11
patella and tibia degrees of freedom. These were solved using
Force-Dependent Kinematics [2]. Patellar ligament was
modeled with 3 elastic springs and overall ligament properties
were adapted from the literature.
•Laxity simulation. We simulated anterior-posterior, varus-
valgus, and internal-external knee laxity, by applying specific
loads to the tibia (see Figure), and a neutral unloaded case as
reference. A constant pulling force of 200 N was applied to
the patella, and the femur was flexed from 0°-120°.
•Evaluation. Knee kinematics were measured using Grood and
Suntay’s definition for the knee joint coordinate system [3].
Laxity in each direction was calculated as the difference
between the values of the loaded and reference case. The
results were then compared with experimental data [4].
Results
Posterior-Anterior tibial drawer laxity:
Valgus-varus laxity: Internal-external rotation laxity:
Discussion and Conclusion
•Overall, the model followed the trends of reported knee joint
laxity for similar experiment and implant type.
•Discrepancies may be due to differences in implant
characteristics, surgical technique, and ligament restraint.
•In presence of subject-specific laxity test data, the knee joint
stability may be further calibrated on an individual basis.
Future work
•We aim at studying the effect of variations in surgical
technique in TKA, such as tibial cut slope, varus-valgus
alignment, and orientation of the femoral component.
References:
[1] M. A. Marra, V. Vanheule, R. Fluit, B. H. F. J. M. Koopman, J. Rasmussen, N. J. J. Verdonschot, and M. S. Andersen, “A
Subject-Specific Musculoskeletal Modeling Framework to Predict in Vivo Mechanics of Total Knee Arthroplasty.,” J.
Biomech. Eng., Nov. 2014.
[2] M. S. Andersen, M. Damsgaard, and J. Rasmussen, “Force-dependent kinematics: a new analysis method for non-
conforming joints,” in XIII International Symposium on Computer Simulation in Biomechanics, 2011.
[3] E. Grood and W. Suntay, “A joint coordinate system for the clinical description of three-dimensional motions:
application to the knee.,” J. Biomech. Eng., 1983.
[4] A. M. J. Bull, O. Kessler, M. Alam, and A. A. Amis, “Changes in knee kinematics reflect the articular geometry after
arthroplasty.,” Clin. Orthop. Relat. Res., vol. 466, pp. 2491–2499, 2008.
Evaluation of laxity tests with a musculo-
skeletal model of Total Knee Arthroplasty.
M.A. Marra¹, M. Strzelczak¹, S. van de Groes², P. Heesterbeek³, A. Wymenga⁴, H.F.J.M. Koopman⁵, D. Janssen¹, N. Verdonschot¹,⁵
¹Orthopaedic Research Lab, Radboud university medical center, Nijmegen, The Netherlands, ²Orthopaedic Department, Radboud university medical center,
Nijmegen, The Netherlands, ³Research Department, Sint Maartenskliniek, Nijmegen, The Netherlands, ⁴Department of Orthopaedics, Sint Maartenskliniek,
Nijmegen, The Netherlands, ⁵Department of Biomechanical Engineering, University of Twente, Enschede, The Netherlands
Marco Marra, PhD student
Marco.Marra@radboudumc.nl
Orthopaedic Research Laboratory
Radboud university medical center
P.O. Box 9101, 6500 HB Nijmegen, The Netherlands
www.biomechanics.nl
-10
-5
0
5
10
0 15 30 45 60 75 90
mm
Knee Flexion, deg
Bull et al.
Model
Anterior
Posterior
-5
-3
-1
1
3
5
0 15 30 45 60 75 90
deg
Knee Flexion, deg
-20
-10
0
10
20
0 15 30 45 60 75 90
deg
Knee Flexion, deg
Varus
Valgus
External rotation
Internal rotation
*adapted, averages over multiple experiments are shown
*
0°
6°
3°
+2 mm
+4 mm
9°
A
Tibial displacement during the
anterior laxity simulation
Acknowledgments:
This research is part of the ERC
project ‘BioMechTools’, funded
by the European Commission
www.erc-biomechtools.eu