There are two options to treat the pain and stiffness of tibiotalar OA: arthrodesis and total ankle replacement (TAR). Arthrodesis involves fusing the tibia and talus and is performed in most patients. With motion completely lost at the tibiotalar joint, 50% of arthrodesis patients are unable to return to their desired activities. Eliminating tibiotalar motion may also force the adjacent joints, including the subtalar, talonavicular, and calcaneocuboid joints to undergo compensatory hypermobility. Although not confirmed, excessive motion may cause OA at these adjacent joints. Total ankle replacement is an attractive alternative to arthrodesis as it may reduce compensatory motion by opening degrees of freedom at the tibiotalar joint. However, 33% of TAR implants fail within 10 years. Also, about 15% of TAR patients develop arthritis at the adjacent joints. With poor 10-year outcomes, TAR remains reserved for older patients. Yet, over a lifetime, younger patients may stand to benefit the most from the functionality offered by TAR. Our ultimate goal is to make TAR a viable option for restoring mobility to patients ? young and old Quantification of in-vivo kinematics (i.e. angles and translations) of the tibiotalar and adjacent joints is essential to design TAR implants that increase longevity and improve functionality. Prior studies have not measured in-vivo kinematics of the tibiotalar joint independent from the adjacent joints in TAR or arthrodesis patients. Our group has developed and validated a dual-fluoroscopy (DF) system that accurately measures in-vivo motion of each joint. DF visualizes motion relative to bony anatomy and implanted hardware, yielding ?joint arthrokinematics?. Arthrokinematic data could identify features of a TAR implant that impede articulation, motivating design changes. These data could also drive computer models that predict stresses at the bone-implant interface to identify modes of TAR failure. We propose an R21 study to measure in-vivo joint arthrokinematics during walking, stair-ascent, and balanced heelrise in: 1) post-TAR, 2) post-arthrodesis, and 3) non-pathologic controls. Compared to controls, we hypothesize: 1) motion of the adjacent joints in arthrodesis patients is increased, 2) motion of the adjacent joints in TAR patients is increased, and 3) motion of the prosthetic tibiotalar joint in TAR patients is reduced. Confirming Hypothesis 1 will provide mechanistic evidence of compensatory motion that is clinically believed to instigate OA in the joints adjacent to the fusion site. In addition, confirmation of Hypothesis 1 will provide rationale to focus future research directives on projects that advance TAR. Demonstrating that hypermobility is not eliminated (Hypothesis 2), and that TT motion is restricted (Hypothesis 3), following TAR will indicate that improvements to TAR are still required. Although an exploratory study, completion of this R21 will yield the only in-vivo measurements of articulation for the tibiotalar and adjacent joints in these cohorts. Importantly, data collected herein will support a body of future research designed to meet our ultimate goal.
The results of this research will yield an improved understanding of how ankle fusion and total ankle replacement change the motions of the primary ankle and adjacent joints. Results will also provide fundamental insight into the biomechanics of normal ankles.
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