our research to help put this together and I'll be presenting. None of us have any disclosures. So femoral head coverage is based on a complex three-dimensional interplay between the femoral head and the acetabulum. Therefore, two-dimensional measurements of a three-dimensional relationship may not accurately reflect coverage. To solve this problem, prior investigations have sought to utilize 3D measurement techniques. However, these investigations have largely focused on nondisplastics hips and typically report global coverage. Dividing the femoral head into quadrants provides a more localized coverage analysis. However, accurate quadrant definition is key to accurate coverage assessment. Existing studies have utilized the femoral head-neck axis for quadrant definition, which may be confounded by femoral torsion and abnormal neck shaft angle. Additionally, this also includes the inferior portion of the femoral head in modeling, which is non-weight-bearing. Prior studies that have tried to isolate the superior weight-bearing portion of the femoral head have reduced it to a best-fit 2D circle, which ignores the complex three-dimensional interplay and curvature of the articulation. Defining quadrants using anatomic planes, isolating the superior half of the femoral head and using 3D surface area-based coverage would be expected to provide a more reliable assessment. Correlating 2D measurements would provide physicians a useful but still practical method of assessment. Therefore, the purpose of this study was to compare the surface area-based 3D acetabular coverage of the superior half of the femoral head by quadrant as defined by anatomic planes in patients with acetabular dysplasia versus controls and to evaluate the relationship between 2D and 3D measures of coverage. The hypotheses were that one, dysplastic patients would exhibit decreased acetabular coverage, and two, LCA would demonstrate a stronger relationship with 3D coverage than with tonus angle. The dysplastic group was comprised of patients that underwent a PAO for acetabular dysplasia with adjunct hip arthroscopy. Patients with tonus grade greater than 1 or a hip disorder other than dysplasia were excluded. A one-to-one match for sex, age and BMI was used to create a control cohort of nondysplastic FAI patients. LCA and tonus angle were measured on standing AP pelvic radiographs. And to perform the modeling, 3D osseous models were first constructed from CT scans. The surface of the acetabulum was then projected onto the surface of the femoral head. Next, anatomic planes were established. First, the anatomic pelvic plane was created with using the bilateral ASIS and pubic protuberance on the affected side. The coronal reference plane was defined as a parallel plane passing through the affected femoral head center. The transverse and sagittal planes were defined as perpendicular relative to that coronal plane. Global coverage was measured as the percent coverage of the superior half of the femoral head. This was further divided by the coronal and sagittal planes into the quadrants we talked about before. So moving to the results, 26 patients were included in each group. There were no significant differences in sex, age or BMI. As expected, LCA was significantly lower and tonus angle was significantly higher in the dysplastic cohort. There were 26 controls without dysplasia, 17 patients with mild dysplasia, 8 with moderate and 1 with severe. As can be appreciated in this figure, as dysplasia increased, femoral head coverage decreased. Global three-dimensional coverage was significantly decreased in the dysplastic cohort compared with controls. When broken down into quadrants, though, in order of magnitude, the anterolateral, posterolateral and anteromedial quadrant coverage was significantly decreased in the dysplastic cohort. However, posteromedial coverage was essentially unchanged in either group. LCA and tonus angle correlated significantly with global coverage and with coverage in each quadrant. However, when compared, correlations between LCA and 3D coverage were significantly stronger than correlations between the tonus angle and 3D coverage. When multiple linear regression was used, LCA was still found to be a significant predictor with the largest effects in the global and anterolateral quadrants. Conversely, tonus angle actually dropped out and was not found to be a significant predictor of coverage. So major findings of the study include, one, dysplastic patients still maintained 100% of coverage in the posteromedial quadrant, suggesting this area is minimally affected by dysplasia. However, it did have significantly less global, anterolateral, posterolateral and anteromedial coverage. Two, LCA was found to be a significant predictor of coverage while tonus angle was not. Three, LCA correlated most strongly with anterolateral coverage. Limitations of the study include, one, that the LCA measurement were made using the source seal which has been shown to assess the anterosuperior coverage versus using the bone edge which would be more direct superlateral or anterolateral. So had we used bone edge, we might get a slightly weaker anterolateral correlation but a stronger posterolateral correlation. In conclusion, dysplastic patients demonstrated maintained PM coverage but had lower global, anterolateral, posterolateral and anteromedial 3D coverage using this novel modeling technique. LCA was a significant predictor of coverage and most strongly correlated with global and anterolateral coverage, whereas tonus angle was not a significant predictor of 3D coverage. Thank you.

femoral head coverage

acetabular dysplasia

3D measurement techniques

quadrant measurement

periacetabular osteotomy (PAO)