ACETABULAR CUP PLACEMENT WITH IMAGELESS NAVIGATION – A RADIOGRAPHIC EVALUATION

Abstract

Introduction: Malpositioning of the acetabular cup component in total hip arthroplasty can result in increased wear, early nonseptic loosening and is the most common cause of dislocation. Previous research has defined a safe zone with an inclination of 40±10 degrees and anteversion of 15±10 degrees. The purpose of this study was to compare cup placement using imageless navigation to a historical control group using CT based measurements.

Methods: 34 patients receiving a primary hip replacement between June 2005 and December 2006 were enrolled in the study. Alignment of the implant is based on the acquisition of landmarks (ASIS and pubic tubercle) and placement of tracking pins into the ASIS. The target position for all patients was 45 degrees of inclination and 15 degrees of anteversion. The position was determined by postoperative Ct scans of the pelvis. This group was compared to a matched control group.

Results: Descriptive statistics revealed that the demographics of both groups were comparable. Mean cup placement in the navigation group was 46.6±5.9 deg of inclination and 18.8±5.6 deg of anteversion. Mean cup placement in the control group was 48.4±8.85 deg of inclination and 22.33±10.9 deg of anteversion. With navigation 73.7% resp 89.5% of cups were placed within the safe zone for inclination resp. anteversion whereas only 56.2% resp. 50% of cups were placed with freehand technique. Taking both inclination and anteversion into consideration 68.4% of cups were placed in the safe zone with navigation. Only 12.5% were placed for both inclination and anteversion were placed into the safe zone.

Discussion: Computer navigation for total joint arthroplasty, if helpful to the surgeon, has to increase reliability of component placement and show a significant reduction in variation compared to freehand techniques. Our results demonstrate that imageless navigation is a reliable tool which significantly increases precision of acetabular cup placement. Further studies are needed to evaluate and further increase the accuracy of the system.