Musculoskeletal Modeling to Provide Muscles and Ligaments Length Changes during Movement for Orthopaedic Surgery Planning

The estimation of muscles and ligaments behavior can be useful in orthopaedic surgery or when a functional restoration may be reached by means of soft tissues surgery, i.e. in each case a different function is necessary to be planned for a muscle. Models of the skeletal muscle system were almost used to predict the rate of muscle-tendon lengthening during the most common tasks. In this work, a more general approach is proposed, in which individual anthropometry was considered through imaging processing, and joint kinematics captured in a movement analysis laboratory was used to animate a skeletal model, with the aim of simulating the effects of different surgical solutions on the muscle system functioning. To attain this result, the integration of different technologies, models and algorithms was required. After developing a model of the musculoskeletal and ligament system, the procedures for the pre-operative planning of both hip and knee joint replacement were simulated. A surgery planning tool based on the previously created model allowed the surgeon to plan an operation through a three-dimensional visualization of bones, by defining components’ sizes and improving their positioning by taking into account not only bone geometry but also the soft tissues spanning the articulations. Since the model is defined on a specific patient, it gives the possibility to increase model’s specificity with the aim of improving planning accuracy. The use of this planning tool can be useful both in pre-operative planning and during the surgical operation because the surgeon can develop skills in performing different operation’s steps. In this work, we considered two examples based on the model of muscles, bones and ligaments that was developed. The main steps of this procedure and the preliminary results are here presented pointing out the feasibility of the planning tool and of the model itself.