Development and validation of a biplane fluoroscopy system to quantify in-vivo knee kinematics

• Main Author: Williams, David Elwyn
• Published: Cardiff University 2018
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.768063

Accurate measurement of in-vivo joint kinematics is important for understanding normal and pathological knee function and evaluating outcome of surgical procedures. Fluoroscopy and model based image registration (MBIR) provides an accurate and minimally-invasive technique for calculating in-vivo kinematics. This study builds upon existing MBIR protocols and looks at quantifying the errors present in the protocols, with the aim of developing a biplane fluoroscopy system to investigate in-vivo kinematics of the knee. A retrospective single plane fluoroscopy study was performed on a unique TKR patient group with mal-aligned knee replacements to understand the influence of surgical frontal plane alignment and function. Significant interactions between frontal plane alignment and knee joint kinetics and kinematics were detected using marker-based motion capture. While these interactions were not replicated within in-vivo knee kinematics measured during a step-up activity using fluoroscopy and MBIR, results highlighted interactions with other surgical measures of alignment such as posterior tibial slope angle and Hip-Knee-Ankle angle. A study was undertaken to examine in-vivo kinematics using three dimensional (3D) models generated from magnetic resonance imaging (MRI) combined with fluoroscopy and synchronised motion analysis. These studies, in which the fluoroscopy was performed at Llandough Hospital X-ray Department, highlighted key technical limitations associated with the currently adopted protocol, and two primary sources of error in determining in-vivo kinematics; generation of three dimensional (3D) bone models and MBIR processing to calculate in-vivo kinematics. A validation protocol was developed to determine the accuracy of magnetic resonance imaging (MRI) derived 3D bone models. This was performed by imaging five ovine hind limbs using MRI and computed tomography (CT) followed by complete dissection and structured light scanning of the femora and tibiae to calculate the true geometry. The results showed that MRI derived 3D bone models had a RMS error of 0.8 mm when compared with the other modalities. This error was deemed acceptable as it was not larger than the 3D voxel dimension. A validation study was performed to investigate the accuracy of a biplane C-arm system in calculating skeletal kinematics using MBIR. It examined the static and dynamic accuracy associated with using both Sawbones and an ovine hind limb during a simulated step up activity. Three different dynamic velocities were investigated. Errors were shown to increase with higher velocities highlighting the importance of calculating errors during representative dynamic tasks. The results also highlighted important hardware limitations with the C-arm system. An in-house combined motion analysis and biplane fluoroscopy system was established at Cardiff University. An updated and validated MBIR protocol was performed on 5 healthy volunteers during a step up and down task. 3D models of bone and cartilage were used in combination with biplane fluoroscopy images to calculate in-vivo kinematics and estimate contact point positions. The validation and MBIR protocols in this thesis have contributed to the development and understanding of the limitations associated with a new unique bespoke biplane X-ray system being designed and manufactured currently at Cardiff University.