Necrosis of the hip, cells and tissues how does it happen?

[Sam S]

In simple terms can you explain to me how this disease occurs? how does changes in the tissues/cells in the bone occur due to disease process?
My partner was diagnosed with this after been on a high doseage of steriods for a brain tumour.
Thanks Dr strong, but can you explain how the cells change? or the tissues change? I am writing this up in a research document as I am going to use the disease in my assigment.

[dr.strongmidicine]

impairs the blood supply to bone... occurs when there is an interruption of the blood supply to the head of the femur (the ball, of the ball-and-socket hip joint) The lack of normal blood supply causes a decrease in delivery of oxygen and nutrients to the bone, and the bone subsequently dies. When the bone dies, the strength of the bone is greatly diminished, and the bone is susceptible to collapse

.No one know exactly what causes hip osteonecrosis. When hip osteonecrosis occurs, the bone collapses and the joint surface, the cartilage, looses its smooth shape. Because the cartilage looses the support of the bone underneath itself, the joint surface is quickly worn away, and arthritis quickly progresses.

Most cases of hip osteonecrosis are associated with either alcoholism or steroid use.