A MULTI-CENTRE EVALUATION OF ACETABULAR CUP POSITINING IN ROBOTIC-ASSISTED TOTAL HIP ARTHROPLASTY

Introduction In total hip arthroplasty, the positioning of the acetabular cup, in particular, has been shown to play an important role in the survivorship of the prosthetic joint. The commonly accepted “safe zone” extends from 5–30° of anteversion to 30–50° of inclination. However, several studies have utilized a more restrictive safe zone of 5–25° of anteversion and 30–45° of inclination, a modification of the Lewinnek zone. Many attempts have been made to develop a more reliable method of positioning the acetabular component. Robotic-assisted surgery is one such method. The purpose of this study was to compare the resulting position of the acetabular component after robotic-assisted surgery with the intraoperative robotic data to determine if improved accuracy can be achieved with the robotic-assisted method. Methods One hundred and nineteen patients received THA, at four different medical centers in the United States, using a haptic robotic arm. Pre-operative CT scans were obtained for all patients and used during the planning of the procedure, at which point the proposed component size and positioning was determined. Preparation of the acetabular bone bed, as well as impaction of the acetabular component itself, was performed using the robotic device. Using an AP Pelvis and Cross-Table Lateral radiograph, each patient9s resulting acetabular inclination and version was measured using the Hip Analysis Suite software. The component position retrieved from the robot was compared to the measured values from the radiographs. The positioning data was compared to two safe zones described above. Results Of the 119 surgeries performed, 110 could be read with the hip analysis suite software. Radiographically, the average inclination was 40.4° ± 4.1° with a range of 27.4°–53.7° and the average anteversion was 21.5° ± 6.1° with a range of 5.2°–42.6°. As measured inter-operatively, 100% of the components fell within the Lewinnek safe zone and 96% fell within the more restrictive safe zone. Radiographically, 88% of the cases fell within the Lewinnek safe zone and 73% fell within the restrictive safe zone. The mean difference between the inclination and version of the component determined by the robot and by radiographic analysis was 0.31° and 2.1° respectively. Conclusions The inclination and version of the acetabular components implanted with robotic assistance as determined inter-operatively were within the commonly accepted limits in all cases. Variations between the cup positions determined inter-operatively and from the post-operative radiographs are related to differences in the radiographic project of the hip and the robotic registration of the pelvis from CT images. In no procedure was the radiographic inclination greater than 54° or version less than 5°. In this study, the use of robotic-assisted positioning of the acetabular component has significantly reduced the variability of component orientation. This improved reliability of positioning should result in an increase of favourable functioning, and a decrease in early complications such as dislocation, impingement, and component wear.