A Comprehensive Testing Program for Shoulder Implant Assessment

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Failure of shoulder implants is a growing concern for both the anatomic and reverse designs - this is where the "ball and socket" is reversed to increase muscle moment arms and reduce joint loads. While there are a number of potential failure modes, loss of the structural integrity of the polyethylene liner component due to creep and wear is a most pressing problem. This is likely due to the excessive loads that occur on the articular surfaces.***With the aging baby-boomer population, the demand for these implants is increasing significantly. Moreover, the elevated activity demands including sport and exercise of this group are also a potential challenge to these implants, as the loads and range of motion are increasing. However, the current biomechanical evaluation of these constructs is, in all probability, not an accurate representation of activity, due to a number of simplifications that have been made related to loading and other factors surrounding the implant and bone modeling in the laboratory and computationally. ***The long-term objective of this program is to elucidate the biomechanics of the implant reconstructed shoulder and produce a comprehensive approach to its evaluation, with special interest in arming the biomechanist with new knowledge related to the mechanical behavior of these constructs. These advances will set the stage for testing methodologies and standards for the assessment of these implants. ***The overarching theme of this Discovery program grant is to "drill-down" and determine the loading and the resultant response of the implant system. Over the 5-year tenure of this work, the specific short-term objectives are to (1) determine the envelope of loads that act at the shoulder joint, and (2) to quantify the response of the implant systems (with special interest in the polyethylene component) when subjected to such loading.***The methodology includes experimental studies to simulate activity in the cadaver arm via developing protocols for a specialized simulator with a focus on high velocity (i.e. dynamic) motions. In addition, a loading device will be developed to apply external loads to the arm as would occur with exercise. These measured loads will then be employed in a "test-bed" to be developed that evaluates the mechanical response of the implant.***It is anticipated that the work proposed herein will revolutionize the understanding load transfer through these shoulder implants and advance our engineering-based treatment of this construct beyond the simplified experimental and computational modeling approaches to date. These developments will also result in the evolution of a state of the art testing program that will permit a wide range of advanced studies on shoulder implants.**