Shunsaku Nishihara

Measurements of pelvic flexion angle using three-dimensional computed tomography.

The purpose of the current study was to evaluate whether safe acetabular component position depends on differences in pelvic location between the supine, standing, and sitting positions. The subjects of the current study were 101 patients who had total hip arthroplasty. Anteroposterior radiographs of the pelvis with the patients in the supine, standing, and sitting positions were obtained preoperatively and 1 year after total hip arthroplasty. Computed tomography images of the pelvis were obtained preoperatively. Using image matching between the three-dimensional computed tomography model and anteroposterior radiograph, pelvic flexion angles with the patient in the supine, standing, and sitting positions were calculated. The mean preoperative pelvic flexion angle was 5° ± 9° (range, −37°–30°) in the supine position, 3° ± 12° (range, −46°–33°) in the standing position, and −29° ± 12° (range, −62°–10°) in the sitting position. Because there was much intersubject variability in pelvic flexion angle, it is not appropriate to determine orientation of the acetabular component from anatomic landmarks. In 90% of the cases, the difference in pelvic flexion angle between the supine and standing positions preoperatively was 10° or less. In 90% of the cases, there was 20° or greater extension of the pelvis from the supine position to the sitting position preoperatively, and the safe range of flexion of the hip from anterior prosthetic impingement in the sitting position was 20° or greater than that in the supine position. Preoperative pelvic position in each case was almost completely maintained 1 year after total hip arthroplasty. It is reasonable to regard the pelvic position in the supine position as the functional pelvic position and proper pelvic reference frame in determining optimal orientation of the acetabular component in 90% of cases before and 1 year after total hip arthroplasty, although an adjustment of orientation of the acetabular component was needed for the remaining cases.

Scintigraphic image patterns in dysplastic coxarthrosis: Evaluation with reference to radiographic findings in 210 hips

Little is known about scintigraphic image patterns in the various stages of coxarthrosis. We assessed bone scintigraphy in 159 patients (210 hips) with dysplastic arthrosis of the hip. Scintigraphic images were divided into 5 types related to the radiographic stages of the disease. The scintigraphic images showed little, if any, uptake in the stage of prearthrosis. In the early stage, we found an increase in uptake in the weight bearing area in 30% of cases. In the advanced stage, more than half of the cases had an increase in uptake in the medial side of the joint and in the weight bearing area. In the terminal stage, a marked increase in uptake in the weight bearing area was commonest. Since the osteoblastic reaction intensified, a marked increase in uptake was seen not only in the weight bearing area, but also throughout the entire joint. These types of scintigraphic patterns, which change with the stage of coxarthrosis, seem to reflect the natural course of the disease. All hips with rapid progression of the disease showed a marked increase in uptake of radionuclide the entire joint at earlier stages.

Clinical applications of a laser guidance system with dual laser beam rays as augmented reality of surgical navigation

We have developed a novel laser guidance system that uses 2 or more laser beam emitters. Two or more fan-shaped beam tracts intersect in a line that can be controlled in any direction by changing the angle and direction of beam oscillation. The laser guidance system draws cross hairs on a target, and the intersection of the cross hairs is the entry point for a drill or wire. After stabilization of this entry point, the system draws 2 or more lines along the guide sleeve. We have used this laser guidance system in 10 total hip arthroplasty (THA) procedures and 1 open-wedge-type high tibial osteotomy (HTO) procedure. In our clinical experience, this laser guidance system has worked well in the operating room. It effectively draws laser cross hairs on the patient to indicate the entry point of straight surgical tools. The direction of the tools was indicated by parallel laser beams projected onto the guide sleeves. The system assisted surgeons with acetabular cup placement and femoral reaming and rasping in THA. It was also useful for screw insertion and drilling of the osteotomy plane in HTO.

Effects of CT threshold value to make a surface bone model on accuracy of shape-based registration in a CT-based navigation system for hip surgery

Abstract To clarify the effects of different CT threshold values used to make computer models on the accuracy of surface registration in a CT-based navigation system, a simulation study was performed using CT data of 30 patients who underwent total hip arthroplasty with navigation guidance. Surface models of the pelvis for use in clinical applications were made by contouring the periosteal boundary at threshold ranging from 140 to 260 Hounsfield units (HU) (mean, 200 HU). In each case, the threshold was determined to be approximately 200 HU, based on the balance between soft tissue noise and surface defects. Ten pelvic surface models were made from each set of CT data, using 10 different CT threshold values ranging from 50 to 320 HU with an increment of 30 HU. The center of the acetabulum was defined as the target point in each set of CT data, so that each set of 10 surface models should have the same reference point for measuring the positional and rotational differences among the models after registration. The average residue of registration reached its nadir was minimum with the 200 HU models, and there were no significant differences in residue of registration among the models made at thresholds ranging from 110 to 320 HU. The target registration errors for position and rotation both showed strong correlation with the residue of registration (R=0.879 and 0.880, respectively). We thus conclude that accurate surface registration can be obtained with computer models made at thresholds ranging from 110 to 320 HU by assessing the balance between soft tissue noise and bone surface defects.

Measurement of Pelvic Tilting Angle During Total Hip Arthroplasty Using A Computer Navigation System

The purpose of this study was to measure pelvic orientation during total hip arthroplasty (THA) in a lateral decubitus position using a computer navigation system with an optical localizer (OPTOTRAK). THA was performed in 17 hips. Much attention was paid to set the patients in neutral axial rotation with the anatomical plane of the pelvis perpendicular to the operating table. After shape-based registration, pelvic orientation was tracked with light emitting diode markers fixed to the pelvis. Measurements were based on the anatomical plane. Mean movement of the pelvis from the supine position to the dislocated lateral decubitus position was 8 degrees posterior (26 posterior to 6 anterior), 3 degrees abducted (6 adduction to 20 abduction), and 4 degrees internally rotated (24 internal to 5 external). This study showed that the pelvis was not always placed in neutral axial rotation, despite the surgical plan. It was further tilted posteriorly and rotated internally when the socket was inserted. This tilt can lead to decreased socket anteversion with conventional alignment guide systems, while unknown pelvic orientation in general can cause socket malposition with such systems. Therefore, intraoperative three-dimensional measurements of pelvic orientation seems to be useful to avoid socket malposition.