Fig. 8.

Diagrams showing the proposed mechanism of the effect of femoral version. In the retroverted femur (left), the femoral head is already relatively rotated into the acetabulum, which decreases the clearance of any head-neck abnormality in flexion and exacerbates cam impingement. In an opposite manner, femoral anteversion (right) may mitigate the effect of an anterior cam deformity but could result in more impact on the posterior rim in external rotation. (Reprinted with permission: Sutter et al. Femoral antetorsion: comparing asymptomatic volunteers and patients with femoroacetabular impingement. Radiology 2012;263:475–483).