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UBC Theses and Dissertations

Leveraging the use of existing C-arms for Roentgen stereophotogrammetric analysis Chung, Vivian W.J.


“You can’t improve it unless you can measure it” is a common sentiment in engineering. For total knee replacement patients, failed implants requiring revision surgery is a significant risk. Our long-term goal, therefore, is to develop and evaluate a protocol that will allow us to accurately measure the full 3D position of an implant in the early post-surgical period in order to detect signs of relative motion occurring between implant and bone. By doing this, we will be able to gain insights into the failure mechanisms behind total knee replacement implants. The 'gold standard' method for measuring relative motion is known as Roentgen Stereophotogrammetric Analysis (RSA) – a technique which extracts 3D information about the implant and bone positions from two roughly orthogonal radiographs. This information can be used to quantify the migration of an implant over time to submillimeter accuracy, a metric that has been shown to reliably predict implant longevity in patients (Pijls 2012). Unfortunately, commercial RSA systems are expensive, which has limited their use in clinical settings. Our goal in this project was to develop an RSA protocol based on C-arm fluoroscopy machines, many of which already exist in most hospitals. We successfully developed such a protocol and evaluated its accuracies and precisions through a series of phantom-based verifications. Results were highly promising: accuracies ranged between -39 to 11 μm for translations and -0.025 to 0.029° for rotations, while system precisions ranged between 16 to 27 μm and 0.041 to 0.059°. This performance was comparable to RSA systems in the literature, where traditional and more expensive radiographic equipment was typically employed. In addition, inter-rater reliability tests also showed a high degree of correlation (ICC > 0.999) between two raters who were trained to use the protocol. We conclude that we have developed an RSA protocol appropriate for measuring relative motion of knee replacement implants in phantoms and cadaveric specimens by leveraging the use of existing C-arm technology. This research places us in position to further develop the protocol for use in extensive prospective clinical assessments – research that can potentially drive future improvements in surgical technique and implant design.

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