Characterization of the mechanical behavior of human knee ligaments: A numerical-experimental approach

Abstract

Abstract-During knee-joint motions, the fiber bundles of the knee ligaments are nonuniformly loaded in a recruitment pattern, which depends on successive relative orientations of the insertion sites. These fiber bundles vary with respect to length, orientation and mechanical properties. As a result, the stiffness characteristics of the ligaments as a whole are variable during knee-joint motion. The purpose of the present study is to characterize this variable mechanical behavior. It is hypothesized that for this purpose it is essential to consider the ligaments mechanically as multi-bundle structures in which the variability in fiber bundle characteristics is accounted for, rather than as one-dimensional structures. To verify this hypothesis, bone-ligament-bone preparations of the ligaments were subjected to series of unidirectional subfailure tensile tests in which the relative insertion orientations were varied. For each individual test specimen, this series of tensile tests was simulated with a mathematical ligament model. Geometrically, this model consists of multiple line elements, of which the insertions and orientations are anatomically based. In a mathematical optimization process, the unknown stiffness and recruitment parameters of the line elements are identified by fitting the variable stiffness characteristics of the model to those of the test series. Thus, lumped parameters are obtained which describe the mechanical behavior of the ligament as a function of the relative insertion orientation. This method of identification was applied to all foUr knee ligaments. In all cases, a satisfactory fit between experimental results and computer simulation was obtained, although the residual errors were lower for the cruciate ligaments (1.0-2.4%) than for the collateral ligaments (3.7-8.1%). It was found that models with three or less line elements were very sensitive to geometrical parameters, whereas models with more than 7 line elements suffered from mathematical redundancy. Between 4 and 7 line elements little difference was found. It is concluded that the present ligament models can realistically simulate the variable tensile behavior of human knee ligaments* Hereby the hypothesis is verified that it is essential to consider the ligaments of the knee as multi-bundle structures in order to characterize fully their mechanical behavior,

Effects of the posterior cruciate ligament reconstruction on the biomechanics of the knee joint: a finite element analysis

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A dynamic model of quadriceps and hamstrings function

“…The knee was modelled as a multiple axes mechanism aiming at reproducing the cruciate ligament constraint. Two rigid bars were hinged to distal femur and proximal tibia and had the same length and orientation of the two cruciate ligaments [5,6,7]. The resulting relative movement was a rotation around a movable axis (1 dof) defined by the intersection of the two cruciate ligaments.…”

Evidence against proteoglycan mediated collagen fibril load transmission and dynamic viscoelasticity in tendon

“…While there is an active debate regarding the relative continuity/interconnectivity of collagen fibrils and how collagen fibrils are effectively cross-linked and/or interwoven to provide structural integrity (Provenzano and Vanderby, 2006), a large number of studies suggest that collagen fibrils are relatively short and assume a discontinuous fibril network (Birk et al, 1997;Dahners et al, 2000;Mosler et al, 1985;Thurmond and Trotter, 1994;Trotter and Koob, 1989). Thus tendon is widely modeled as a fiber reinforced composite material in which force is laterally transferred between neighboring fibrils (Ciarletta et al, 2008;Haut, 1986;Humphrey and Yin, 1987;Korhonen et al, 2003;Lanir, 1978;Mommersteeg et al, 1996;Preston and Meyer, 1971;Wren et al, 2003). However, the mechanism that governs lateral load transfer among collagen fibrils is largely unknown.…”