Aseptic bone necrosis

Question:
I am a diving instructor and DAN member working in the Red Sea and have always dived to a maximum of 30 metres. I have recently started doing technical diving to depths of 45 to 55 metres and have heard that deep diving can lead to bone necrosis(osteonecrosis).
What is current medical opinion on this?
Does all diving lead to this, or only dives below a certain depth?
If all diving can cause it, does diving between 30 to 55 metres significantly increase the chance of it developing?

Answer:
Aseptic Bone Necrosis (ABN) is a known long term adverse effect and complication of commercial diving, especially linked to either very prolonged shallow air diving or to deep artificial mixture diving when diving techniques involving very prolonged exposures are involved (such as saturation diving for instance).
Recreational diving has not normally been related to this kind of dysbaric risk, as the bottom times and overall exposures are typically relatively short.
The possibility of ABN is theoretically present also in recreational diving, and, notwithstanding the many studies and publications, not enough is known about ABN to make any definite statement pro or against this probability.
Epidemiologically, however, reports on ABN related to recreational diving, irrespective of the depth, breathing mixture or diving technique, are extremely rare. This seems to apply also to the increasingly popular "technical Diving" techniques, even if it must be said that the amount of specific data is still insufficient and the time interval is still short, considering the fact that ABN, as I said, is a late complication.
ABN is, in essence, considered to be a late complication of previous, possibly repeated, minor or even unrecognized episodes of decompression illness and, as such, is to be considered a bubble related disorder. Its prevention is, therefore, linked to the prevention of excessive bubbling during ascent and decompression, such as it is the current goal of the majority of modern decompression calculation algorhythms.