<prompt> A 45 year old was given steroids after renal transplant. After 2 years he had difficulty in walking and pain in both hips. Which one of the following is most likely cause -Primary osteoahritisAvascular necrosisTuberculosisAluminum toxicity  <response>: High dose coicosteroid alcohol abuse are the commonest causes of avascular necrosis,the commonest site being femoral head.the mechanism is intravascular thrombosis-hyperlipidemia fatty degeneration of liver;fat embolism give rise tocapillary endothelial damage,platelet aggregation thrombosis. reference:Apleys,9th edition,page no104 