Fig. 1

Surgical procedure, as shown in pre- and postoperative radiographs and intraoperative photographs. a Representative intraoperative fluoroscopic image at CD. b Photograph of a cylindrical bone taken by CD. The bloody zone is healthy, and the yellowish-white part on the right is the osteonecrotic part. Reverse IBG was performed. Postoperatively, the gap was repaired. Core defects in the healthy zone were supplemented with artificial bone avoiding fracture. c, c’ Changes on AP X-ray. d, d’ Changes on LAT X-ray. Downward yellow arrows indicate the gap made by femoral head collapse, while the upward yellow arrow indicates repair of the femoral head sphericity by IBG. CD, core decompression; IBG, impaction bone graft; AP, anteroposterior; LAT, lateral