"The ilioischial line, also known as the Köhler line, is a radiologic feature seen in the AP pelvis view and serves to assess the posterior acetabular column 1-4."
"If in addition, the femoral head is medial or close to the ilioischial line and medial to the acetabular walls this is a sign of protrusio acetabuli 4, which itself can be seen in osteoarthritis, rheumatoid arthritis, post-traumatic hip joints 4, osteogenesis imperfecta 6, or Paget disease."