Accurate placement of total knee arthroplasty (TKA) components is critical for obtaining good long-term clinical outcome. Several contemporary CT- or MRI-based technologies allow surgeons to pre-plan TKA and translate that planning into the operating room. To evaluate TKA component placement, post-operative CT or MRI scans allow comprehensive 3D measurements. However, these are expensive and difficult to obtain in large numbers, and yield an additional radiation dose to the patient (in case of CT). A potential solution to overcome these hurdles exists in using 2D/3D registration techniques. In this technique, a new tool (the X-ray Module, Mimics®, Materialise NV) is used to align one or more post-operative X-rays with the preoperative CT- or MRI-based 3D planning (Figure 1). The aim of this study was to determine the accuracy of this 2D/3D registration technique for determining 3D position of TKA implant components postoperatively. A TKA was performed in six human cadaver legs. A CT scan was acquired preoperatively and the bones were segmented using Mimics® to obtain 3D bone models. Post-operatively, a high-resolution CT scan with minimization of metal scatters was acquired and bones and implant components were segmented in Mimics® to obtain the ground truth for their relative position. To apply the novel X-ray based post-op analysis, conventional anteroposterior and lateral radiographs were obtained. The accuracy of the X-ray tool was determined by calculating the angles (varus/valgus, flexion/extension, external/internal rotations) and the distances (anterior/posterior, proximal/distal, medial/lateral) between the centers of gravity of the implants from the X-ray based method and the CT-based ground truth in the anatomical coordinate system of the bone. X-ray based alignment was assessed by an orthopedic surgeon (3 repetitions) and Bland-Altman plots were created to visualize the differences between the ground truth and the X-ray based assessment of the implant position.Introduction
Materials and Methods
