Development and Experimental Validation of an Impactor for Osseointegrated Transfemoral Implant Stability Assessment
Creators: Beaudry, Eric C
Publisher: name: University of Alberta Library
Year: 2024

<p>Osseointegrated transfemoral implants are a promising alternative for individuals who are unable to use a socket prosthesis; it is generally accepted that bone-anchored prostheses can improve patient quality of life. Osseointegration is the long-term process of implant anchorage in bone, caused by the interdigitation of bone at the implant surface; remodelling at the bone-implant interface is responsible for the stability of the implant over time. Osseointegrated dental implants have been studied extensively, and several research and commercial devices have employed vibration analysis to quantify their stability. Such approaches assume the bone-implant interface has an effective stiffness that governs the dynamic response of the bone-implant system. In general, the interface stiffens with progressed osseointegration, and the natural frequencies of the system increase over time. The Osstell and Advanced System for Implant Stability Testing (ASIST) are two devices that leverage this behaviour to monitor osseointegration. The Osstell employs resonance frequency analysis, while the ASIST uses a percussion method in conjunction with an analytical model of the bone-implant system. The ASIST has demonstrated better sensitivity and reliability than the Osstell in a benchtop study, as it accounts for the inertial and geometric properties of the implant itself. The success of the ASIST approach in a variety of applications has made it an attractive option for transfemoral implant stability assessment. To date, a handful of studies have demonstrated the potential of vibrational analysis in transfemoral implant stability assessment, and a parallel investigation established the ability of the ASIST approach to isolate mechanical properties of the bone-implant interface. However, there is currently a need for a novel impactor to increase the sensitivity of the approach. In line with the state of the ASIST approach, four objectives were outlined for this thesis:</p>

<ol>
<li>Develop an impactor for osseointegrated transfemoral implant stability assessment.</li>
<li>Integrate the impactor with a mathematical model and the ASIST approach.</li>
<li>Enhance the sensitivity of the approach in the full interface stiffness range.</li>
<li>Validate the safety, reliability, and sensitivity of the integrated approach.
Four project phases were executed in the development and validation of an impactor for transfemoral implant stability assessment. In the first phase, a benchtop prototype was developed, and a variety of factors were explored for inclusion in a prospective development and evaluation study. Factor exploration was conducted with backing from experimental modal analysis theory and led to a comprehensive framework for the development study. The second phase involved the execution of the study and produced design specifications for impact rod mass, tip geometry, and impact interface stiffness. Tests were conducted on benchtop transfemoral amputation models under three bone-implant interface stiffness conditions. Silicone rubber adhesive, paraffin wax, and superglue simulated low, intermediate, and high stiffness interfaces, respectively. The results indicated that multiple impact rod masses (10;30 𝑔) and impact interface stiffnesses (316 stainless steel; Delrin®) should be included in subsequent phases, as a single optimal configuration was not apparent. Full domain sensitivity was preliminarily demonstrated for a combination of prototype impactor configurations. In the third phase, two handpieces were designed and manufactured with the recommended impact rods and interchangeable impact tips. Sufficient safety and functionality of the 30 𝑔 impactor was demonstrated, and it was deployed in a parallel clinical study. A design of experiments methodology was synthesized for the last stage of the project, an experimental validation study. Three operators took measurements with both handpieces on various implant configurations under the same interface stiffness conditions as the development study (low; intermediate; high). An objective framework for 1D finite element model matching and measurement trustworthiness judgements was developed for analysis. The 10 𝑔 impactor demonstrated superior interface stiffness sensitivity and classification accuracy relative to the 30 𝑔 impactor.
A novel impactor for osseointegrated transfemoral implant stability assessment was developed and validated in a benchtop study. The selected impactor demonstrated high sensitivity to a wide range of bone-implant interface stiffness conditions and was able to correctly classify all measurements for a simple implant configuration. The enclosed thesis represents a significant achievement in the field of transfemoral implant stability assessment, detailing the first device to implement an electromagnetic impactor, vibration acquisition system, and 1D finite element model in a strong approach to osseointegrated transfemoral implant stability assessment.</li>
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