Avascular Necrosis of the Femoral Head
Avascular necrosis or osteonecrosis is death of a segment of bone due to disruption of the blood supply. Extraosseous or intraosseous interruption of the venous or arterial blood flow.
AVN of the femoral head usually occurs due to fractures of the femoral neck or a hip dislocation. Trauma to the deep branch of the Medial Femoral Circumflex Artery may occur with antegrade rod placement during piriformis entry in children.
A posterior dislocation of the femoral head should be reduced in an expedited way to decrease the risk of thrombosis of the vessels which supply the femoral head. Osteonecrosis develops in about 2-20% of hips that are reduced within 6 hours. The risk of osteonecrosis will increase with delay in reduction of the hip. Osteonecrosis appears within two years after the injury. It is evident within one year in most patients.
If a patient has a Pipken fracture, the patient should be informed about the complications of AVN preoperatively. Fixation failure is associated with osteonecrosis or nonunion. The effect of the anterior approach on osteonecrosis is not known. Stress fractures should be pinned before displacement occurs — displacement will have a bad result. Osteonecrosis can be clinically significant when followed by lateral segmental collapse. The more vertical the fracture, the greater chance that AVN will occur.
In acetabular fracture fixation, during intraoperative dissection for an acetabular fracture reduction and fixation, avoid injury to the ascending branch of the medial femoral circumflex artery (MFCA). Fractures of the hip in children are associated with a high rate of osteonecrosis. Four types can be identified.