In a prospective and randomised clinical study, acetabular cups were implanted free-hand (control group n=25) or with computer assistance using an image-free navigation system (study group n=25). Total hip replacement was performed in lateral position and through minimally invasive anterior approach (MicroHip). The cup position was measured postoperatively on pelvic CT using the CT-planning software.

An average inclination of 42.3° (range: 35°–56°; SD±8.0°) and an average anteversion of 24.0° (range: −5° to 54°; SD±16.0°) were found in the control group, and an average inclination of 45.0° (range: 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 10/25 of the cups in the control group were within the Lewinnek safe zone, 18/25 of the cups in the study group were placed in this target region (p=0.003). We saw no disadvantage compared to previous studies in supine position with standard approach.