How does prednisone cause avascular necrosis?

Still unknown: Even though there is this very well-established connection between chronic Prednisone use and avascular necrosis, how this occurs remains unclear. Numerous hypotheses abound. Some argue that increased lipids seen with steroids cause vessels to joints to clog, leading to oxygen starvation & bone death. A more popular view is that vessel (venous) walls undergo thickening, leading to poor blood flow.