The peripheral soft tissues should not be ignored in the finite element models of the human knee joint

Medical & Biological Engineering & Computing, Dec 2017

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.

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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)


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Hamid Naghibi Beidokhti, Dennis Janssen, Sebastiaan van de Groes, Nico Verdonschot. The peripheral soft tissues should not be ignored in the finite element models of the human knee joint, Medical & Biological Engineering & Computing, 2017, pp. 1-11, DOI: 10.1007/s11517-017-1757-0