Physician Assistant Clinical Knowledge Rating and Assessment Tool (PACKRAT) 4 Practice Exam

The blood supply to the femoral head is mainly via vessels that run along the femoral neck inside the joint capsule. A fracture through the femoral neck can disrupt these retinacular arteries, particularly branches of the medial femoral circumflex artery, cutting off the head’s blood supply. Without adequate perfusion, the bone tissue dies, leading to avascular necrosis. Fractures that are extracapsular, like intertrochanteric or subtrochanteric injuries, tend to spare these intracapsular vessels and thus have a lower risk of AVN. Pelvic rim fractures don’t directly jeopardize the femoral head’s blood supply, so they’re not associated with AVN risk to the head. Therefore, a femoral neck fracture carries the greatest risk of avascular necrosis.