Is hyperbaric oxygen a beneficial treatment for avascular necrosis ?

No: No it has no effect for this diagnosi.

Femoral Head : What an interesting question. A number of small studies suggest that it may be helpful for treatment of stage-i avascular necrosis of the femoral head. This is a little ironic since saturation diving can lead to dysbaric osteonecrosis (type of avascular necrosis) of the femoral head. See below.