Do you recommend medical therapy for extensive atraumatic osteonecrosis of the femoral head to mitigate pain or prevent femoral head collapse?

This is a good question. Extensive atraumatic ON of the femoral head will probably not respond to any medical therapy; eventually, the patient will need a replacement. However, ON that is from a systemic insult (drugs, alcohol) is often bilateral so if the other hip is less affected or not affected, then a trial of hPTH (1-34) might work, as it can stimulate angiogenesis and new bone formation around the ON lesion. However, this is an opinion and it has not been studied in an RCT.