MICROSTRUCTURAL MODELING OF FIBER KINEMATICS AND BIOMECHANICS OF THE HUMAN FACET CAPSULAR LIGAMENT DURING SUBFAILURE LOADING

摘要

Whiplash and other traumatic neck injuries are a primary cause of chronic neck pain in the United States, with the cervical facet joint and its ligament being a common anatomical source of the pain. During these injuries, the facet capsular ligament undergoes excessive stretching that alters the subsequent mechanical function of the facet joint and can also initiate pain [1,2]. Accordingly, defining the mechanical response of the facet capsule requires understanding its microstructural response during loading. Although the macro-mechanical responses of ligaments for many types of loading and injury scenarios have been studied, the microstructural and fibrillar responses in the facet capsular ligament remain largely undefined.Mathematical models have been developed to predict the responses of individual ligament fibers [3-5]. Although such models capture stress-strain responses or failure behavior, many approaches use overly-simplified representations of the ligament microstructure and are unsuitable for the anisotropic, inhomogeneous structure of the facet ligament. One set of models developed by Lanir uses strain energies to quantify fibrillar and tissue stresses [3]; the strain energies are influenced by the crimp of each unstretched collagen fiber. Also, that model assumes affine behavior with fibers reorienting with the local deformation, often towards the axis of loading [3]. While such assumptions simplify the modeling algorithms, there is no evidence to support their being appropriate for application to the facet capsule, which is planar and has variable fiber orientation. The goal of this study was to develop a computational model that includes both mechanical and fiber kinematic components in order to predict tissue stress and fiber rotation in the human facet capsule, and to begin to assess whether the assumption of affine behavior is valid for modeling human facet capsule ligament microstructural responses.