Subject specific kinematic analysis of an implanted ankle joint

The ankle joint complex is composed of several joints which give rise to a complex range of movements, governed byinteractions between ligaments and articular surfaces. Degenerative processes and traumatic injuries compromise the healthy functionality of the joint, with osteoarthritis being the primary concern. Total ankle replacement (TAR) has emerged in the past decades for being a viable alternative to arthrodesis, offering promising outcomes in the mid-term. Numerous designs have been proposed over years. The latest stage of innovation involves in silico pre-operative planning to optimize implant design and positioning. In this research, FAR total ankle replacement by Adler Ortho is analysed in detail. The primary objective of this thesis is to develop a method for estimating the subject-specific passive kinematics of an implanted ankle; secondarily, to assess the influence of implant positioning and its geometric parameters on the resulting motion. A mathematical model, tailored to subject specific anatomy, is employed to reproduce passive plantar-dorsiflexion motion of the ankle joint. Concurrently, a geometric analysis of the implant constraints establishes an analogy between the components relative motion and a planetary gear mechanism. A virtual arthroplasty is performed in order to obtain relative positioning of the implant with respect to some anatomical landmarks. By integrating both the physiological passive motion model and the mechanical constraint of the implant, an estimation of the ankle range of motion for passive plantar-dorsiflexion after implantation is obtained. Additionally, the impact of different proximal-distal positioning and insert thicknesses is evaluated. The results demonstrated that a more proximal positioning of the implant and the use of a thinner insert both contribute to a larger range of motion. Finally, based on these findings, guidelines for optimizing implant positioning to enhance post-operative kinematics are proposed.