Intra-op measurement of the mechanical axis deviation: an evaluation study on 19 human cadaver legs

The alignment of the lower limb in high tibial osteotomy (HTO) or total knee arthroplasty (TKA) must be determined intraoperatively. One way to do so is to deform the mechanical axis deviation (MAD), for which a tolerance measurement of 10 mm is widely accepted. Many techniques are proposed in clinical practice such as visual inspection, cable method, grid with lead impregnated reference lines, or more recently, navigation systems. Each has their disadvantages including reliability of the MAD measurement, excess radiation, prolonged operation time, complicated setup and high cost. To alleviate such shortcomings, we propose a novel clinical protocol that allows quick and accurate intraoperative calculation of MAD. This is achieved by an X-ray stitching method requiring only three X-ray images placed into a panoramic image frame during the entire procedure. The method has been systematically analyzed in a simulation framework in order to investigate its accuracy and robustness. Furthermore, we validated our protocol via a preclinical study comprising 19 human cadaver legs. Four surgeons determined MAD measurements using our X-ray panorama and compared these values to a gold-standard CT-based technique. The maximum average MAD error was 3.5mm which shows great potential for the technique.