Legg-Calve-Perthes (LCP) Disease is idiopathic avascular necrosis of the proximal femoral epiphysis in children. The lateral pillar classification of LCP disease is determined from anteroposterior radiographs of the pelvis made in the early fragmentation stage of the disease. The lateral pillar is defined as the lateral portion of the femoral head, on the anteroposterior radiograph, that is demarcated from the central portion of the head by a lucent line of fragmentation. Treatment is typically observation in children less than 8 years of age and femoral and/or pelvic osteotomy in children greater than 8 years of age.