Fig. 4

Representative magnetic resonance images. a Preoperative coronal T1-weighted magnetic resonance imaging (MRI) showing osteonecrosis of the femoral head (ONFH) that occupied the weight-bearing portion and extended laterally to the acetabular edge. b–d MRI scan of the ONFH area and the femoral neck region 6 months and 1 year postoperatively, showing continued low signal intensity, indicating the influence of the traumatic procedure. e MRI scan 18 months postoperatively, showing the first change of signal intensity at the drilling route. The drilling site at the femoral neck is changing to the normal signal intensity of the bone. f Most recent MRI scan 2 years postoperatively, showing almost normal signal intensity at the ONFH area. The area and size of ONFH decreased at the weight-bearing surface (yellow arrow)