Cam Morphology and Sex-Based Differences in the Proximal Femur Anatomy of Collegiate Athletes Without Hip Pain: A 3-Dimensional Statistical Shape Modeling Analysis.

Background: Radiographic studies have reported a high prevalence of cam morphology in athletes, especially in male athletes, suggesting these individuals are at an elevated risk of developing femoroacetabular impingement syndrome (FAIS). However, recent research has shown that 2-dimensional measurements do not accurately characterize cam deformities, motivating the need for 3-dimensional (3D) analyses.

Purpose: To develop a 3D statistical shape model of the proximal femur to evaluate cam morphology in collegiate athletes through (1) quantifying shape variation, (2) establishing sex-based shape differences, and (3) comparing shapes between male athletes and male cam FAIS patients.

Study design: Cross-sectional study; Level of evidence, 3.

Methods: Double-echo steady-state magnetic resonance images were prospectively acquired of the hips of Division I collegiate athletes (28 male, 23 female). An existing data set of computed tomography scans of cam FAIS patients (26 male) and morphologically screened controls (30 male, 17 female) was also evaluated. The proximal femur was segmented, reconstructed into a 3D surface, and analyzed to generate a correspondence model using ShapeWorks. Principal component analysis, parallel analysis, and linear discriminant analysis quantified variation in proximal femoral shape.

Results: Variation in the full cohort primarily occurred in the head-neck junction, femoral offset, and location of the greater trochanter relative to the head/neck (mode VIII, adjusted P = .01; modes I and IV, adjusted P = .002 and adjusted P = .003, respectively; modes IV and VIII, adjusted P = .0003 and adjusted P = .0007, resepctively. P < .001). Modes represented anatomic variation significantly different between pairs within a group. Variation between male and female athletes occurred in the concavity of the head at the head-neck junction, length of the femur, and length of the femoral offset (modes I and II, adjusted P = .006 and adjusted P = .009, respectively). Variation between male athletes and male patients and between male patients and male controls occurred in the concavity of the head at the head-neck junction and femoral torsion (mode IV, adjusted P = .02 and adjusted P = .003, respectively). Shape scores, which represented a generalized value of the entire shape, were significantly different between athletes and patients (adjusted P = .003) and patients and controls (adjusted P < .0001).

Conclusion: Athletes in our study had a proximal femur shape more similar to morphologically screened controls than FAIS patients. Sex-based differences occurred in athletes in regions where cam morphology typically occurs.