Femoral Neck-shaft Angle Differs but Femoral Anteversion is Constant in Osteological Specimens with and without a Cam Deformity of the Proximal Femur

Abstract

The factors leading to the development of a cam deformity of the proximal femur currently remain unknown, but it is believed that the deformity is related to growth and development. The geometry of the proximal femur, including the neck-shaft angle and anteversion angle, influences the forces acting across the developing physis with gait. We have performed an anatomic study of the proximal femur in order to define potential differences in proximal femoral morphology associated with the presence or absence of a cam deformity, and we hypothesized that differences in both femoral neck-shaft angle and femoral anteversion angle may be present between groups. We obtained 357 matched tibiae and femora from the Hamann-Todd Osteological Collection (Cleveland, OH) and measured the following: femoral head-neck alpha angle, femoral anteversion, and femoral neck-shaft angle. We then divided these specimens into two groups based upon alpha angle < 45° (Group 1, 73 specimens) or alpha angle > 60° (Group 2,122 specimens), and all other specimens were excluded from analysis. We then performed an independent samples t-test to evaluate for differences in measured parameters between groups using this subset of 195 specimens. The mean alpha angle in Group 1 was 40.9° +/- 3.3°, and the mean alpha angle in Group 2 was 67.0° +/- 5.6°. The mean femoral anteversion was 15.5° +/- 15.8° in Group 1 versus 13.8° +/- 15.9° in Group 2 (p=0.48). The mean femoral neck-shaft angle was 140.4° +/- 6.7° in Group 1 versus 133.2° +/- 28.1° in Group 2 (p=0.008). The presence of an alpha angle > 60° was associated with a lower femoral neck-shaft angle, and there was a high degree of variation in femoral neck-shaft angle for specimens with alpha angle > 60°. No difference in femoral anteversion was identified between these groups. It is possible that a more varus neck-shaft angle may result in altered distribution of forces across the femoral physis and thereby be contributory to the development of a cam- type morphology.