Computational Investigation of the Creep Behaviour of Human Knee Joint under Realistic Loading and Contact Boundary Conditions

Transcription

1 Computational Investigation of the Creep Behaviour of Human Knee Joint under Realistic Loading and Contact Boundary Conditions Qingen Meng 1, Zhongmin Jin 1,2, Ruth Wilcox 1, John Fisher 1. 1 Institute of Medical and Biological Engineering, School of Mechanical Engineering, University of Leeds, Leeds, United Kingdom, 2 School of Mechanical Engineering, Xian Jiaotong University, Xian, China. Disclosures: Q. Meng: None. Z. Jin: None. R. Wilcox: None. J. Fisher: 1; DePuy Synthes Joint Reconstruction. 2; DePuy Synthes Joint Reconstruction. 3A; Tissue Regenix plc. 3B; DePuy Synthes Joint Reconstruction, Invibio, Tissue Regenix. 4; Tissue Regenix plc. 5; DePuy Synthes Joint Reconstruction, Mathys, Invibio. Introduction: The knee joint supports the body and facilitates locomotion for human daily living. An essential load support mechanism of the knee joint is the multiple mechanical contacts between its hydrated soft tissue components, articular cartilage and menisci. Therefore, the biphasic mechanical characteristic of these soft tissues plays an essential role in the functions and pathology of the knee joint. Characterizing the creep behaviour of the knee joint is important for understanding the mechanical function of these soft tissues and the mechanical environment of the knee joint. However, due to the natural complexity of the problem, the previous three-dimensional finite element (FE) knee joint contact mechanics models that considered these soft tissues as biphasic materials were limited to unrealistic conditions, such as light load and non-zero fluid flow pressure out of contact area [1]. Therefore, the aim of this study was to characterize the time-dependent contact behaviour of intact and meniscectomy knee joints under realistic loading and fluid flow contact boundary conditions, using finite element method. Methods: The geometry of the investigated human tibio-femoral joint was from the Open Knee Project [2]. Both intact (Figure 1) and meniscectomy knee joints in full extension position were simulated. Cartilage and menisci (only applicable for the intact knee) were considered as biphasic materials. The tensile properties of the cartilage and menisci were considered. The material properties of the cartilage and menisci are summarized in Table 1. Bone was assumed to be rigid [10]. The tibia was fully fixed. For the femur, the rotation in the flexion/extension direction and the translation in the transverse plane were fixed. A vertical load of 800 N was applied to the femur in 1 second and kept constantly for 1500 seconds. Six biphasic contact pairs for the intact knee and two for the menisectomy knee were defined. The FE models were solved using FEBio (Version 1.5.0) [11], where the contact dependent fluid flow contact boundary conditions were satisfied automatically.

2 Results: For the intact knee, when the load was just applied (1 s), the contact mainly took place between the meniscus and the cartilage; the contact area between the menisci and tibial cartilage was larger than that between the tibial and femoral cartilage. The peak maximum compressive stress occurred at the interfaces between tibial cartilage and menisci (Figure 2 a). With the increase of time, the contact area between the tibial and femoral cartilage increased and the peak maximum compressive stress was at the cartilage-cartilage interfaces at 1500 s (Figure 2 b). After menisectomy, compared with the intact knee model, during the whole process of creep, the stress on the tibial cartilage was markedly increased, by 140% at 1 s and 84% at 1500 s for the peak value (Figures 2 c and d). Moreover, the stress at the lateral condyle centre of the menisectomy joint was markedly higher than that of the medial condyle centre (Figures 2 c and d). While for the intact knee, they were approximately at the same level during the whole creep period (Figures 2 a and b).

3 The fluid pressure level at the condyle centres of both the intact and menisectomy knee joints remained remarkably high for 1500 seconds (Figure 3). However, for the intact joint, the fluid pressure at the cartilage-meniscus interfaces decreased notably rapidly than that at the condyle centres (Figure 3).

4 Discussion: The variation in the contact areas and stress distributions at the cartilage-meniscus and cartilage-cartilage interfaces implied that when the load was just applied, the meniscus supported a larger part of applied load (about 75%). When the creep developed, more force was transferred to the interface between the tibial and femoral cartilage. The comparison of the stress between the intact and menisectomy knee joints indicated that the menisci reduced the stress on the cartilage by two mechanisms: increasing contact area and redistributing the stress between the two compartments. The high level fluid pressure at the condyle centres is desirable for protecting the cartilage. However, the rapid decrease in the fluid pressure at the cartilagemeniscus interface may have adverse implications for the cartilage in those regions. Significance: The time-dependent contact behaviour of intact and meniscectomy knee joints was investigated under realistic loading and contact boundary conditions for the first time. The findings obtained from this study are important for understanding the mechanical environment, the biomechanical functions of the components, and potentially the pathology of the knee joint. Acknowledgments: This study was supported by the EPSRC Programme Grant Biotribology of Cartilage and WELMEC, a Centre of Excellence in Medical Engineering funded by Wellcome Trust and EPSRC (Grant no: WT088908/Z/09/Z), and partially by the NIHR as part of collaboration with the LMBRU. J.F. is an NIHR Senior Investigator. References: [1] Li, in Modeling and Simulation in Engineering, InTech, NY, USA, 2012, [2] Sibole, 34th Annual Meeting of the American Society of Biomechanics, 2010, Providence, RI. [3] Athanasiou, J Orthop Res, 1991, 9: [4] Akizuki, J Orthop Res, 1986, 4: [5] Keenan, Comput Methods Biomech Biomed Eng, 2009, 12: [6] Chia, J Orthop Res, 2008, 26: [7] Sweigart, Ann Biomed Eng, 2004, 32: [8] Lechner, J Orthop Res, 2000, 18: [9] Tissakht, J Biomech, 1995, 28: [10] Donahue, J Biomech Eng, 2002, 124: [11] Mass, J Biomech Eng, 2012, 134: ORS 2014 Annual Meeting Poster No: 0802

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