The obtruator foramen is the opening created by the ischium and pubis bones of the pelvis. This obtruator is triangle in shape in females and oval shape in males.
When the right obturator foramen has been narrowed, the coccyx and sacrum has been rotated toward the left hip and the right ischial spine has been demonstrated without the pelvic brim of the superimposition. This represents the RPO (right posterior oblique position.
