Complex sentence: Complications arise mainly because the sheet of the iliopsoas muscle pushes circumflex artery against the neck of the femur and decreases blood flow to the femoral head, so the Frejka pillow is not indicated in all the forms of the developmental dysplasia of the hip.
Split into simpler sentences: Complications arise mainly because the sheet of the iliopsoas muscle pushes circumflex artery against the neck of the femur and decreases blood flow to the femoral head. That is the reason why the Frejka pillow is not indicated in all the forms of the developmental dysplasia of the hip.