Reduced variability of acetabular cup positioning with use of an imageless navigation system

Positioning the acetabular component is one of the most important steps in total hip arthroplasty; malpositioned components can result in dislocations, impingement, limited range of motion, and increased polyethylene wear. Conventional surgery makes use of specialized alignment guides provided by the manufacturers of the implants. The use of mechanical guides has been shown to result in large variations of cup inclination and version. We investigated acetabular cup alignment with the nonimage-based hip navigation system compared with a conventional mechanically guided procedure in 12 human cadavers. Postoperative cup position relative to the pelvic reference plane was assessed in both groups with the use of a three-dimensional digitizing arm. In the navigated group, a median inclination of 45.5degrees and a median anteversion of 21.9degrees (goals, 45degrees and 20degrees) were reached. In the control group, the median inclination was 41.8degrees and the median anteversion was 24.6degrees. The ninetieth percentile showed a much wider range for the control group (36.1degrees-51.8degrees inclination, 15degrees-33.5degrees anteversion) than for the navigated group (43.9degrees-48.2degrees inclination, 18.3degrees-25.4degrees anteversion). This cadaver study shows that computer-assisted cup positioning using a nonimage-based hip navigation system allowed for more consistent placement of the acetabular component.