Orthopedic Biomechanics: Multibody Analysis

Joints of the musculoskeletal apparatus are characterized by high complexity, being described by three-dimensional kinematics, which results from the concurrence of translational and rotational motions among the articulating bones forming the joint. The complexity of the kinematics derives from the interaction of different anatomical structures, and, in particular, ligaments play a critical role in defining joints’ range of motion, since they represent the major articular restraining elements. An alteration of the balancing among the constraining actions exerted by the ligaments, together with the other soft tissue surrounding the joint, leads to modifications in the joint kinematics and, consequently, to the establishment of detrimental intraarticular loading conditions. In order to alleviate pain caused by pathological conditions and to restore the functionality of the joint, different orthopedic surgical approaches can be pursued, such as corrective osteotomies and prosthesis implantation. Over the past few years, the introduction of even more sophisticated mechanical tools and computer-assisted surgical systems has made it possible to improve the accuracy of the procedures and, thus, to enhance surgical outcomes. Nevertheless, obtaining essential information such as intraarticular contact pressure and soft tissue tensioning still remains a challenge or at times even impossible to measure during a surgical intervention in an operative room. In this context, the integration of computational simulations into the surgical decision-making process appears to be an appealing solution to address this problem and to quantify surgical parameters that, usually, are just qualitatively evaluated. In particular, the multibody modeling of joints has proven to be an effective approach to estimating significant quantities, such as forces related to ligaments, tendons, muscles, and intraarticular contacts, in addition to relative motions between bones. Moreover, the development of even more accurate patient-specific biomechanical models, coupled with surgical navigation systems and specifically designed sensing devices, could lead to a better understanding of the joint biomechanics as well as to the implementation of valuable tools aimed at supporting surgeons throughout the pre-, intra-, and postoperative phases, providing additional data enabling foreseeing consequences of surgical interventions and also improving actual surgical techniques. In this chapter, various multibody modeling strategies are proposed, which might prove useful in investigating specific orthopedic issues related to the biomechanical behavior of anatomical and artificial joints. In addition, case studies related to anatomical, injured, and prosthetic joints are presented, in order to provide application examples of the modeling strategies proposed.