Acetabular positioning is more consistent with the use of a novel miniature computer-assisted device

Introduction Computer-assisted surgery (CAS) relying on registration of the anterior pelvic plane (APP) allows precise acetabular component placement. We determined the variability of cup placement in patients who underwent THA with and without the use of CAS that does not rely on the registration of APP. Methods Fifty-one patients who underwent staged-bilateral THAs, one without CAS (control), and a subsequent one with CAS (study group), were included. Acetabular inclination and anteversion were measured on standardized post-operative radiographs. Variance in cup position and Lewinnek's zone proportionality were compared between the groups. Multiple regressions were performed to identify factors affecting variability in acetabular component placement. Results The mean inclination for the control and study group was 42.7 degrees (SD 4.5) and 42.5 degrees (SD 2.9), respectively. The inclination variance was 20.5 degrees and 8.2 degrees respectively (p = < 0.001). Cup inclination was more consistent in the study than in the control group (deviation from the mean: 2.3 degrees vs. 3.8 degrees, p < 0.001). The mean anteversion for the control and the study group was 25.5 degrees (SD 7.4) and 26.8 degrees (SD 4.3), respectively. The anteversion variance was 54.2 degrees and 18.2 degrees respectively (p = <0.001). Consistency in cup anteversion was significantly improved with CAS (deviation from the mean: 3.4 degrees vs. 5.8 degrees; p = 0.002). Lewinnek's zone proportionality was not affected by the use of CAS. In the linear regression analysis, CAS significantly increased consistency in cup inclination (p = 0.01). Patient's factors including BMI and laterality affected consistency of cup placement. Conclusion CAS without referencing the APP allows a more consistent orientation of the acetabular component when compared to freehand placement.