Abstract
A kinetostatic model able to replicate both the natural unloaded motion of the tibiotalar (or ankle) joint and the joint behavior under external loads is presented. The model is developed as the second step of a sequential procedure, which allows the definition of a kinetostatic model as a generalization of a kinematic model of the joint defined at the first step. Specifically, this kinematic model taken as the starting point of the definition procedure is a parallel spatial mechanism which replicates the ankle unloaded motion. It features two rigid bodies (representing the tibia-fibula and the talus-calcaneus complexes) interconnected by five rigid binary links, that mimic three articular contacts and two nearly isometric fibers (IFs) of the tibiocalcaneal ligament (TiCaL) and calcaneofibular ligament (CaFiL). In the kinetostatic model, the five links are considered as compliant; moreover, further elastic structures are added to represent all the main ankle passive structures of the joint. Thanks to this definition procedure, the kinetostatic model still replicates the ankle unloaded motion with the same accuracy as the kinematic model. In addition, the model can replicate the behavior of the joint when external loads are applied. Finally, the structures that guide these motions are consistent with the anatomical evidence. The parameters of the model are identified for two specimens from both subject-specific and published data. Loads are then applied to the model in order to simulate two common clinical tests. The model-predicted ankle motion shows good agreement with results from the literature.
Highlights
Understanding the role of the passive structures of human joints, such as ligaments, cartilage and articular surfaces, is fundamental to figuring out how these structures restrain the joint motion and how they sustain the external loads applied to the joint
2 Methods According to the sequential approach [10, 11], the new kinetostatic ankle model is defined at the second step of the procedure, by a proper generalization of a kinematic model obtained at the first step
5 Conclusions A new kinetostatic model of the tibiotalar joint has been proposed in this study
Summary
Understanding the role of the passive structures of human joints, such as ligaments, cartilage and articular surfaces, is fundamental to figuring out how these structures restrain the joint motion and how they sustain the external loads applied to the joint. A better comprehension of the passive structure role would help to identify articular damage in a patient, to assess the efficacy of orthopedic treatments and to design new and more effective prosthetic devices. Articular mathematical models can be useful in this context, since they make it possible to obtain data that cannot be measured on a patient, like forces exerted by ligaments and between articular contact surfaces, extending the present knowledge of human joints [1]. Models have a predictive potential and could show the effects that surgical operations, prostheses, orthopedic treatments or rehabilitation have on a patient [2]. Though a general description of the joint behaviour can be obtained through the use of models based on mean data, models based on anatomical data measured on a single subject provide a more accurate description of the joint behaviour for the subject itself
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