What is the proper rotation of the lower limbs for an AP projection of the pelvis?

The correct amount of rotation of the lower limbs for an AP projection of the pelvis is 15° medial. This specific rotation is essential for aligning the femoral necks parallel to the imaging receptor. Properly positioning the lower limbs helps to minimize any foreshortening of the femoral necks and ensures optimal visualization of the pelvic anatomy.

When the limbs are rotated medially, the greater trochanters of the femurs are positioned in a more posterior aspect, which can help prevent overlap with the pelvic structures. This technique improves the diagnostic quality of the radiograph, allowing for better assessment of the hip joints, pelvis, and the surrounding anatomical structures.

In contrast, other degrees of medial rotation would not achieve the ideal orientation of structures, potentially leading to suboptimal imaging. A rotation that is too slight may result in overlapping anatomical features, while excessive rotation could distort the appearance of the hip joints and surrounding ligaments and structures, making it harder to accurately diagnose any potential issues.