Computer-assisted surgical navigation has been introduced into orthopedic surgery to increase precision and to improve the postoperative success of hip osteotomies and replacement. This technology allows for greater precision, which allows for a more patient-specific approach but requires that differences in acetabular geometry be assessed. Incorrect orientation of implant components results in decreased range of motion and instability of the hip. Mean acetabular anteversion and abduction angles have been established with an average range of 16-20(and 30-45°, respectively. These geometries can vary significantly from individual to individual, and similar studies have found a difference between anteversion of the left and right femur and tibia. We hypothesize that acetabular geometry will vary significantly between the right and left hip, and this study hopes to document that asymmetry. Twenty-five well-preserved pelvic samples were selected from a collection of Nubian skeletons at the University of Colorado. The age and gender of each specimen were determined by anthropologic technique. The frontal plane of each pelvis was defined by laying a grid on the anterior superior illiac spines (ASIS) and pubic tubercles so that all points were in contact with the surface. The rim of each acetabulum was traced using a Coordinate Measuring Machine (CMM) with ± 0.02 mm accuracy and analyzed using Rhinoceros software. Three different researchers took three measurements of each acetabulum, and a best-fit plane was defined. Acetabular angles were determined by comparison between the acetabular plane and derived sagittal and transverse planes. An interclass correlation was performed to determine inter- and intraobserver reliability. A paired t-test was used to determine significance. The mean left anteversion of the measured samples was 18.3 ± 7.7 and the mean right anteversion was 20.8 ± 7.1. The mean difference between left and right acetabular anteversion was -2.4, with a p value of .05. There was a 97% and 94% confidence interval established for inter- and intraobserver reliability, respectively. Our data support the hypothesis that there is a significant difference between left and right acetabular anteversion. Large standard deviations about the mean indicate a large degree of intersubject variability. These data further support the hypothesis that acetabular angles are specific to each hip. Minimal inter-/intraobserver variability validates the repeatability of our technique.
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