Development of imageless computer navigation for acetabular component position in total hip replacement

Abstract

The purpose of this study was to develop an imageless (without preoperative computerized tomography (CT) scans or intraoperative fluoroscopy) computer navigation system for total hip replacement. One-hundred and ninety-five hips were operated with imageless computer navigation. Eighty-five hips were operated prior to obtaining precise results, with precision refined in the subsequent 110 hips. Computer accuracy for cup-adjusted anteversion was achieved in 100% of the final 40 hips, and for adjusted inclination in 96.6%. The factors necessary for accurate measurements are mechanical stability of the tools with the light-emitting diodes, adjusted computer anteversion and inclination for the tilt of the pelvis (tilt in the AP plane), and check-and-balance techniques for confirmation of measurements of tilt, anteversion and inclination.

Figures

Figure 1

The AP plane of the pelvis is being registered with the pointer guide on the anterior iliac spine. The pelvic base with the light-emitting diodes on the tracker and the pointer are seen by the optical camera at the head of the table which is attached to the hardware for the navigation system. The computer screen is on a separate piece of equipment.

Figure 2

The AP plane of the pelvis is registered with the patient in the supine position by touching the digitizing probe to the bone of the two ASIS and pubis.

Figure 3

The patient is in the lateral position for the operation and supported by two pelvic and two chest supports. The two posterior supports are those touched by the registration pointer to register the longitudinal axis of the body. The registration of the long axis of the body is done by creating a triangle on the two posts. This figure illustrates the triangle with two points on the pelvic post. A second tilt measurement is done with the triangle reversed with two points on the chest post. The pelvic and femoral antennae with light-emitting diodes are shown.

Figure 5

The acetabular bone is touched by the pointer guide as seen in the lower left-hand quadrant. The computer screen shows the outline of the AP and ML dimensions of the acetabulum with the medial bone marked by yellow dots. The lighter central dot measures the center of rotation of the hip. This is seen in the upper two quadrants. The lower right quadrant shows the inclination and anteversion of the native acetabulum as determined by the fit plane.

Figure 6

The reamer in the acetabulum is shown in the lower left-hand quadrant. The position of the reamer relative to the acetabular peripheral bone and medial wall is shown in the upper two quadrants. The CC is center of rotation (positive number means superior displacement); ML is mediolateral displacement from the center of rotation by the reaming (negative number means medial displacement); AP is the anterior-posterior position of the reamer (negative number means posterior displacement). The numbers on the left give the angular position of the reamer in the acetabulum both by inclination and anteversion, which is also adjusted.

Figure 7

The cup implantation is shown in the lower left quadrant. The upper quadrant shows the position of the cup relative to the acetabular bone including medial wall. The CC, ML and AP numbers provide the center of rotation superior displacement (CC), medialization (ML) and AP displacement (AP). The numbers on the left give the numerical inclination and anteversion, and AdjAV and AdjI. The lower right quadrant gives the native acetabulum values, and the gray lines show what portion of the cup would be uncovered. The amount of coverage is only illustrative.

Figure 8

The measurement of the fit plane of the acetabular cup is done by touching the metal edge of the cup at six points with the registration pointer.