CT-based navigation system in total hip arthroplasty (THA) is widely used to achieve accurate implant placement. Now, we developed our own CT-based navigation system originally, and since then we have been conducting various analysis in order to use the system more effectively. We compared the accuracy of registration with this navigation system and land mark matching type navigation system. In this study, we evaluated the influence of the surgical approach to the accuracy of registration. Between June 2015 and February 2016, 28 consecutive uncemented THAs were performed in 26 patients. The preoperative diagnosis was osteoarthritis in 20 hips, osteonecrosis of the femoral hips in 5, and rheumatoid arthritis in 3. The newly developed navigation system was a CT based, surface matching type navigation system. We used newly developed navigation system and commercially available land-mark type CT-based navigation system in the setting of acetabular sockets under the same condition. After we fixed the cementless cup, we measured the cup setting angle of inclination and anteversion on each navigation system. Postoperative assessment was performed using CT one week after the operation, and measured the actual angle of the cup. Approach of operations were performed via posterolateral approach in 14 hips, and Hardinge approach in 14 hips. We calculated the absolute value of the cup angle difference between intra-operative value and post-operative value with each navigation system and compared the accuracy between each navigation system and surgical approach.Introduction
Methods
CT-based navigation system in total hip arthroplasty(THA) is widely used to achieve accurate implant placement. However, its internal structure was a trade secret. Therefore, it was hard to analyze optimal reference points. Now, we developed our own CT-based navigation system originally, and since then we have been conducting various analyses in order to use the system more effectively. The purpose of this study was to analyze the optimal area and the number of registration points, which enables to move initial errors into the acceptable range. We set the anterior pelvic plane(APP) as the reference plane, and defined the coordinates as follows: X-axis for external direction, Y-axis for anterior direction, and Z-axis for proximal direction. We made pelvic bone models after THA, a normal shape and acetabular dysplasia model, and performed registration using an originally developed CT based navigation system. At first, we registered point paired matching at 4 points, and surface matching was performed at 53 points, which were placed around the acetabulum. 20 points were on anterosuperior, 10 points were on posterosuperior, 20 points were on posterior around the acetabulum, and 3 points were on the pubis. We selected surface matching points based on the actual operation approach, calculated the accuracy of the error correction, and searched the optimal area and the number of surface matching points.Object
Methods
CT-based navigation system in total hip arthroplasty(THA) is widely used to achieve accurate implant placement. The purpose of this study was to evaluate the influence of initial error correction according to the differences in the shape of the acetabulum, and correction accuracy associated with operation approach after localization of registration points at anterior or posterior area of the acetabulum. We set the anterior pelvic plane(APP) as the reference plane, and defined the coordinates as follows: X-axis for external direction, Y-axis for anterior direction, and Z-axis for proximal direction. APP is defined by the anterior superior iliac spines and anterior border of the pubic symphysis. We made a bone model of bilateral acetabular dysplasia of the hip, after rotational acetabulum osteotomy(RAO) on one side, and performed registration using infrared-reflective markers. At first, we registered the initial error on navigation system, and calculated the accuracy of the error correction based on each shape of the acetabulum as we increased the surface matching points. Based on the actual operation approach, we also examined the accuracy of the error correction when concentrating the matching points in anterior or posterior areas of the acetabulum.Background
Methods
ROBODOC is a well known tool for a computer assisted arthroplasty. However, the incision tends to enlarge with the system because of the restriction of range of motion. We have developed the robot system for minimally invasive arthroplasty. This report shows the accuracy of our system composed of original planning software, navigation and bone cutting robot. We took the DICOM data of cadaver knees from computed tomography. The data were transferred to the workstation for planning. Matching points for registration and cutting planes were determined on the planning software. Cutting tool was the 6th robot which was able to recognize the locations of its apex and the cadaver knee with navigation system. We made five planes for TKA and two planes for UKA on femur. Then we made one plane on tibia. We evaluated the accuracy by measurement the location of cutting plane under navigation system and by CT data. The registration errors of femur and tibia were less than 1.0mm about cadaver knees. The errors of cutting planes were 1.3 mm about the distal end of femur and 0.5 mm about the proximal end of tibia. The accuracies of the angles of cutting planes were 1.9 degrees and 0.8 degrees compared to the mechanical axis. The errors of anterior and posterior plane of femur were increased compared to the distal plane. It was because the accuracy of registration were correct in axial direction but was not satisfied in rotational direction. The error was considered by the location of points which decided the rotation alignment. We will make effort to minimize the errors of registration and put it into practical use as soon as possible.
