Femurs in patients with hip dysplasia have fundamental shape differences compared with cam femoroacetabular impingement

Figures

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  Fig. 1.. 3D descriptors of femoral head asphericity and proximal femur shape variation. Asphericity—subject-specific 3D reconstructions from CT were cut at the head–neck junction using principal curvature, and spheres were fit to each head; the distance between the head and sphere was calculated across the entire head surface and fitting errors were determined. Shape Variation—3D reconstructions were tightly aligned and cropped at the lesser trochanter; correspondence points were then placed on each femur and SSM was applied to determine the proximal femur variation that existed in DDH and FAI groups; shape variation was presented using PCA modes.

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  Fig. 2.. Radiographic descriptors of the femoral head and acetabulum. The α angle was measured as the angle between the femoral neck axis and the point of beginning asphericity. HNO was the distance between a line parallel to the femoral neck axis and tangent to the anterolateral neck, and a second parallel line tangent to the anterolateral head. NSA on the anteroposterior view was the angle between the femoral neck axis and the long axis of the femur. AI was the angle between a line parallel to the inter-ischial-tuberosity line (line 1) at the inferior aspect of the acetabular sourcil and a second line from the inferior to lateral aspects of the sourcil. LCEA was the angle between a line perpendicular to line 1 originating from the center of a femoral head best-fit circle and a second line from the center of the circle to the lateral aspect of acetabular sourcil.

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  Fig. 3.. PCA Mode 1 contained 53.76% and 41.63% of the total DDH and FAI variation, respectively. Color plots show the distance from the mean at ± 2 SD. Common shape variation (red arrows) was in the NSA and associated vertical distance from the lesser trochanter to the superior femoral head. DDH femurs had unique variation (black arrows) in the shape of the femoral head.

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  Fig. 4.. PCA Mode 2 contained 13.10% and 20.96% of the total DDH and FAI variation, respectively. Color plots show the distance from the mean at ± 2 SD. Common shape variation (red arrows) was in the height of the greater trochanter relative to the femoral head, with greater variation seen in the FAI group. DDH femurs had unique variation (black arrows) in the shape of the femoral head. FAI femurs had unique variation in head–neck junction shape.

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  Fig. 5.. PCA Mode 3 contained 9.11% and 12.86% of the total DDH and FAI variation, respectively. Color plots show the distance from the mean at ± 2 SD. Common shape variation (red arrows) was in the horizontal femoral offset. DDH femurs had unique variation (black arrows) in the shape of the femoral head. FAI femurs had unique variation in the contour of the great trochanter and proximal femoral torsion.