C-Arm fluoroscopy is limited by its 2D imaging modality and is incapable of providing accurate 3D quantitative assessment of operative anatomy. In High Tibial Osteotomy (HTO), assessing the distance between the mechanical axis of the leg and the centre of the knee joint is difficult to accomplish due to limited fluoroscopic view size. A previously developed sensor-based tracking system (TC-Arm)adds on to C-arm equipment to provide additional quantitative capabilities. A new image-based tracking module was developed for TC-Arm using a reference panel with an array of fiducial markers. The image analysis software segments the marker positions in each image and identifies image coordinates with respect to the panel. Each image's parameters are identified by 2D-3D matching of the panel's 3D model to the marker's epipolar geometries. Finally, the defined linear transformation matrices are applied for positioning all the fluoroscopic images with respect to the same global reference. A Sawbone model of the leg was used as a phantom and marked with radio-dense fiducial markers at the centres of each joint.

An Optotrak optoelectronic tracking system data was used to validate the new module's functions. First, tracking accuracy was determined by comparing orthogonal-stereo views and the reconstructed positions of the panel's design. Secondly, TC-Arm's results were compared to the corresponding digitised references points on the Sawbone model to calculate errors in the varus/valgus angle and mechanical axis deviation. The new addition to the TC-Arm has a reasonable tracking accuracy (<3.6mm, <4°) considering HTO: The system measured the mechanical axis deviation for HTO application with an accuracy of 1.3 mm and 1.4°. Comparing these results with the acceptable tolerance of less than 10 mm for MAD reported in the literature, our demonstrated results are considered to be within an acceptable range. With the new module, the capability for three-dimensional quantitative assessments of operative anatomies of any size can be added to any C-arm equipment in the OR. This can have great potential for many complex orthopaedic trauma, reconstruction, or preservation surgeries including HTO.