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 (range: 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).