If you had to boil it down, what is avascular necrosis?

Dead bone: Avascular necrosis (avn) is a disruption of the blood supply to a bone. With no blood supply, the bone is substantially weakened there are numerous causes, most commonly trauma/fracture. Common bones involved are the hip, shoulder, scaphoid, femoral condyles.

DEAD BONE: Avascular necrosis means the blood fow to a joint or bone has been comprimised and causes dead bone. One of the most common areas affected is the hip joint as there is very little blood flow to the femur bone in the hip joint. Other areas that can be affected include the wrist and ankle. Any bone or joint affected by trauma can be affected. Of course it is not extremely common.