The peripheral soft tissues should not be ignored in the finite element models of the human knee joint
The peripheral soft tissues should not be ignored in the finite element models of the human knee joint
Hamid Naghibi Beidokhti 0 1 2
Dennis Janssen 0 1 2
Sebastiaan van de Groes 0 1 2
Nico Verdonschot 0 1 2
0 Laboratory of Biomechanical Engineering, University of Twente , Enschede , The Netherlands
1 Orthopaedic Department, Radboud University Medical Center , Nijmegen , The Netherlands
2 Orthopedic Research Laboratory, Radboud Institute for Health Sciences, Radboud University Medical Center , 6525 GA Nijmegen , The Netherlands
In finite element models of the either implanted or intact human knee joint, soft tissue structures like tendons and ligaments are being incorporated, but usually skin, peripheral knee soft tissues, and the posterior capsule are ignored and assumed to be of minor influence on knee joint biomechanics. It is, however, unknown how these peripheral structures influence the biomechanical response of the knee. In this study, the aim was to assess the significance of the peripheral soft tissues and posterior capsule on the kinematics and laxities of human knee joint, based on experimental tests on three human cadaveric specimens. Despite the high inter-subject variability of the results, it was demonstrated that the target tissues have a considerable influence on posterior translational and internal and valgus rotational laxities of lax knees under flexion. Consequently, ignoring these tissues from computational models may alter the knee joint biomechanics.
Finite element method; Knee laxity; Knee peripheral tissues; Knee posterior capsule; Kinematics
1 Introduction
The finite element (FE) method is being widely utilized as
a research tool to investigate knee biomechanics [
1
].
However, every FE model of either native or implanted
knees suffers from limitations and simplifications [
2
]. In
even the most comprehensive FE model of the knee, soft
tissue structures like tendons and ligaments are being
incorporated, but usually skin, peripheral soft tissues, and the
posterior capsule are ignored, mostly due to the lack of
experimental data on their influence on the joint
kinematics and laxity [
3, 4
] (Fig. 1). On the other hand, only a few
studies modeled posterior capsule in either native (i.e.,
*
Shin et al. [
5
]) or implanted (i.e., Baldwin et al. [
6
]) knee
models, roughly approximating the properties based on the
limited experimental data of Brantigan and Voshell [
7
]
(Fig. 1c). The influence of these peripheral structures on
the biomechanical behavior of the knee joint is largely
unknown and usually assumed to be of minor influence
on the overall kinematics of the knee joint.
Geiger et al. reviewed the posterolateral and posteromedial
soft tissue structures [
8
]. LaPrade et al. verified the
quantitative anatomy of medial structures of the knee joint including
the posterior oblique ligament [
9
]. None of them, however,
assessed the properties of their target tissues. A few studies
investigated the effect of the lateral soft tissues, and more
importantly of the popliteofibular ligament and popliteal
tendon, on varus and external rotational laxities under limited
loading conditions [
10–13
]. Their results indicated that the
popliteofibular ligament contributes to posterolateral stability
[12] and prevents excessive posterior translation and varus
angulation [
11
], especially when the knee is flexed [
13
].
Sugita et al. indicated that the popliteal tendon and
popliteofibular ligaments are equally important in
posterolateral stability of the knee [
10
]. Griffith et al. measured the
oblique popliteal ligament (OPL) force at different loading
conditions and indicated that it takes part in the internal and
Fig. 1 A posterior view of a schematic human knee joint (reproduced
from [
8
] Elsevier license permission 3932521102554) (a); a typical FE
model of a native knee joint (reused from [
14
], the original image was
horizontally flipped and labeled) (b); and an FE model with posterior
capsule inclusion (reproduced from [
6
] Elsevier license permission
3981261251500) (c)
valgus rotational stiffness at low flexions [
15
]. Rachmat et al.
estimated the mechanical properties of posterior capsule based
on isolated ex situ uniaxial tensile tests [
16
]. Their results
showed asymmetrical mechanical properties in the medial,
central, and lateral regions. However, the outcome based on
the isolated ex situ testing condition could only be correlated
to a limited knee gesture (hyper-extension).
The influence of the peripheral structures and posterior
capsule on knee joint laxity has not been completely described in
the literature, but is of interest for computational modelers. The
aim of this study, therefore, was to assess the significance of the
peripheral soft tissues and posterior capsule on the kinematics
and laxity of the human knee joint. Accordingly, a
computational approach to model the target tissues in FE was sought.
Fig. 2 The six-DOF knee testin (...truncated)