Three-dimensional CT measurement of adult acetabular dysplasia: technique, preliminary results in normal subjects, and potential applications

Objective. To assess a three-dimensional computed tomography (3DCT) technique for measurement of acetabular coverage in adults. Design, We used 3DCT to define the geometric centre of the femoral head and to measure centre-edge angles (CEAs) at 10 degrees rotational increments around the acetabular rim. The means, ranges, standard deviations and 95% confidence intervals for the CEAs at the various rotational increments were determined. Inter- and intra-observer variability was measured. The normal values are compared with two example cases of acetabular dysplasia. Patients. The normal hips of 15 subjects aged 19-49 years (mean 34.2 years) were measured. Results. The 3DCT measurements are reproducible (mean difference interobserver, 1.7 degrees-7.9 degrees; mean difference intra-observer, 0.6 degrees-6.9 degrees). Mean normal CEA at the lateral rim was 33 degrees with a 95% confidence interval of 23 degrees-43 degrees, Mean normal CEAs at 10 degrees rotational increments from anterior to posterior rim were determined, and graphed as a 'normal curve'. Conclusion. This new 3DCT method of assessing acetabular dysplasia is simple, reproducible, and applicable to diagnosis, quantification and surgical planning for adult acetabular dysplasia patients.