The blood supply of the femoral head depends critically on the medial femoral circumflex artery (MFCA) posterior retinacular vessels, which enter the femoral head at the base of the femoral neck and run in the retinaculum to penetrate the subchondral bone of the weight-bearing zone. The MFCA supplies approximately 70-80% of the femoral head vascularity. Three zones are described: zone 1 (posterosuperior, at highest risk for AVN), zone 2 (anterosuperior), and zone 3 (inferior, most reliably perfused from the ligamentum teres artery).
Disruption of the femoral head blood supply causes avascular necrosis (AVN, osteonecrosis). Femoral neck fractures in the high posterior retinacular vessel territory (displaced intracapsular fractures, Garden III-IV) carry 25-30% AVN risk from vessel disruption at the capsular insertion. The Ficat staging and the ARCO classification grade AVN from stage 0 (normal imaging with perfusion deficit) through stage IV (femoral head collapse with secondary arthritis). Risk factors beyond trauma include corticosteroids, alcohol, sickle cell disease, and coagulopathy.
Displaced intracapsular femoral neck fracture (Garden III-IV) disrupts the posterior retinacular vessels of the medial circumflex femoral artery running along the neck to supply the posterosuperior femoral head, producing AVN in 25-30% of cases; total hip arthroplasty for established AVN with femoral head collapse restores function.
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