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° (range: 30°–53°; SD±7.0°) and an average anteversion of 24.0° (range: −3° to 51°; SD±15.0°) were found in the control group, and an average inclination of 45.0° (ranage: 40°–50°; SD±2.8°) and an average anteversion of 14.4° (range: 5°–25°; SS±5.0°) in the computer-assisted study group. The deviations from the desired cup position (45° inclination, 15° 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).