Greater accuracy in positioning of the acetabular cup by using an image-free navigation system

In a prospective and randomised clinical study, acetabular cups were implanted free-hand (control group n=22) or with computer assistance using an image-free navigation system (study group n=23). The cup position was determined postoperatively on pelvic CT. An average inclination of 42.3 degrees (range: 30 degrees-53 degrees; SD +/- 7.0 degrees) and an average anteversion of 24.0 degrees (range: -3 degrees to 51 degrees; SD +/- 15.0 degrees) were found in the control group, and an average inclination of 45.0 degrees (ranage: 40 degrees-50 degrees; SD +/- 2.8 degrees) and an average anteversion of 14.4 degrees (range: 5 degrees-25 degrees; SS +/- 5.0 degrees) in the computer-assisted study group. The deviations from the desired cup position (45 degrees inclination, 15 degrees anteversion) were significantly lower in the computer-assisted study group (p < 0.001 each). While only 11/22 of the cups in the control group were within the Lewinnek safe zone, 21/23 of the cups in the study group were placed in this target region (p=0.003).