Three dimensional kinematic and surface interaction analysis of a novel total ankle replacement surface design using a numerical model of the hind foot
Ankle joint end stage osteoarthritis can be a deliberating condition that is often not treated due to lack of viable treatment options. The current standard of treatment is total ankle fusion which does not only limit mobility but can lead to further complications with neighboring joints. Alternative treatment uses the currently improving Total Ankle Replacements (TAR). Until recently, TAR have been widely unsuccessful due to the accepted design based off a dated assumption which states that the ankle is a one degree of freedom joint with a fixed axis of rotation. Similar to improvements made to knee implants after the proper kinematics of the knee were noted, the TAR have improved when work done by many researchers concluded that the ankle joint is not a one degree of freedom joint and that it doesn't have a fixed axis of rotation for any of its degrees of freedom. This study proposes a novel design for a TAR based off of a novel morphological study done by Siegler et. al. and analyzes the kinematics and interactions of the novel articulating surfaces compared to traditional TAR designs.
The proposed method of analysis uses a currently available 3-D dynamic model of the hind foot to assess ankle joint kinematics and articulating surface interactions by looking at the results of range of motion, kinematic coupling, ligaments strains and spatial distance mapping of the articulating surfaces. Five different models were analyzed. A Natural model of the hind foot, an Inman design based on the dated morphological study done by Inman, a Conic and Cylindrical designs based on current fashions of TAR and a novel Anatomical design based on the morphological study done by Siegler.
The results of the study supported the notion that the ankle is not a one degree of freedom joint and that it did not have a fixed axis of rotation. Range of motion was found to be slightly increased compared to the natural ankle with the novel Anatomical design while the traditional designs have not delivered the same range of motion. Kinematic coupling was found to be similar across the five models, which hinted to the larger role ligaments play in kinematic coupling. Ligament strain analysis found that the Anatomical design allowed for major ankle joint ligaments to be strained similar to that of the Natural model. Articulating surface interactions were similar to that of the Natural model in the Anatomical design due to the anatomically similar saddle geometry of the implant surface design compared to the natural anatomy.M.S., Biomedical Engineering -- Drexel University, 201
