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Dysbaric 0steonecrosis [nRecreational Diving

3Y PETAR DENOBLE, MD, DSC. ysbaric osteonecrosis (DON) is the destruction of tissue in the long , hips and shoulders associated with diving and D compressed-air work. Generally considered to )e the result of circulation disruption, osteonecrosis can ccur without exposure to changes; indeed, cases )f osteonecrosis that are unrelated to diving far outnumber :ases of DON. Recognized risk factors for osteonecrosis nclude chronic steroid use, coagulopathies, alcoholism, ;moking, antiretroviral drugs and many other conditions. rhe annual prevalence of symptomatic osteonecrosis in he general population is estimated at 0.2 to 0.5 percent. In it-risk populations, such as people with HIV, a prevalence of 5.6percent was reported. The association between and , )steonecrosis was initially suspected because of an dives, but so far there is no indication DON affects them inexpectedly high incidence of osteonecrosis among divers more than recreational divers. This may be due to safe md compressed-air workers. In the 1970s, the estimated decompression protocols or the use of more , or it )revalence was 2 to 5 percent in Navy divers, 25 to 35 may be underdiagnosed. )ercent in tunnel workers, 16 to 55 percent in commercial Occurrence of DON is not necessarily associated with livers in the U.K. and 50 to 65 percent in fishermen divers. a history of (DCS).Most cases of [n comparison to the risk of osteonecrosis in the general DON are asymptomatic at the time of onset and remain so opulation, the risk of DON was 10 times greater in Navy for life. However, if damage occurs near a joint, over the livers and 100 times greater in fishermen. The risk increased years that joint may collapse and cause significant pain and with greater deviations from safe decompression procedures. disability. Such patients usually require joint replacement, DON does not seem to be a problem for recreational which involves major and expensive surgery. Thus, DON livers. There are very few reported cases, and some of represents a major in diving with a minimal risk in these may have resulted from causes other than diving. and an unknown risk in . Diversrisk DON with significant inert gas ioading followed y inadequate decompression. Recognized recreational What are the risk factors for DON? lepth and time limits minimize the risk of DON. However, some recreational divers exceed these limits by engaging in Emmanuel Gempp, M.D.: There is extensive medical harvesting or other commercial activities or by practicing literature dealing with this topic that goes back to the extreme exposures as in technical diving. Turkish scuba 1970s,but it deals primarily with professional divers and divers have been found to be at increased risk of DON, compressed-air workers. Although gas-bubble formation but they seem to disregard safe decompression practices. during decompression is the primary cause of DON, Technical divers, on the other hand, make deep and long it alone may not be sufficient to cause ischemic bone

44 FALL2012 Fromtop: Patient undergoing MRI;MRIof osteonecrosis in the hips Are recreational divers at risk for DON? ‘ nit - . Toldu: Limited studies have shown that DON is not a signific risk for recreational divers.The risk might increasewith violationsof decompression rules and depth or time limits.TI decompression algorithms currently being used in recreatiom divingare safeenough that DON is unlikelyif there are no oti predisposingfactors for osteonecrosis. I.h Gempp: The prevailing view is that recreational divers are at lower risk than commercial divers and compressed-air workers since they are supposed to perform dives with conservative exposures. Some anecdotal cases were observ in the past decade, but the few studies that attempted to determine the prevalence of DON among recreational dive failed to demonstrate the presence of asymptomatic bone lesions using magnetic resonance imaging (MRI). However, repeated musculoskeletal DCS in the same location seems to put divers at increased risk of DON. We recently showed with MRI that scuba divers who experienc repeated DCS (which in 85 percent of cases was shoulder pain) developed definite DON lesions in 19 percent of cases. Those affected were mainly experienced divers who performed repetitive, long, deep air dives using dive computers and did not violate decompression procedures. We also observed that paradoxical, increasing pain during first hyperbaric treatment might be a prognostic sign of D(

necrosis [bone death from lack of circulation] . Dive- development. Since 2004 we have actively followed divers related factors associated with DON include the number of who experienced musculoskeletal DCS. So far there are 33 lifetime dives, dive depths greater than 115 to 130 feet and divers in this cohort. It appears that being older than 40 an empirical decompression procedures. Diver-related factors experiencing delays to recompression of more than six hou include previous musculoskeletal DCS (limb bends), older increase risk of DON. Our findings strongly suggest that age, excessive alcohol consumption, high cholesterol and routine MRI examination is justified in recreational divers coagulation abnormalities. Some researchers suspect rapid treated for limb bends before they return to diving. rates of compression and increased of oxygen. Kawashima: Yes. Compared to technical divers, the numb Mahito I(awashima, M.D., Ph.D.: The main risk factor of cases among recreational divers is much smaller, but sot is a history of musculoskeletal DCS. This was established cases are reported. by many studies that screened divers for DON, and it was confirmed by experimental studies with sheep. Inadequate Does technical diving expose divers to a higher risk of DO decompression is another big factor. Divers such as fishermen who decompress empirically instead of following standard Kawashima: Yes. Deep divers, especially,are at high risk. decompression procedures are at high risk. Obese divers This was shown by a group screening of Japan Agency for should be careful, too. Marine-Earth Science and Technology (JAMSTEC)divers which three divers among 30 were found to have DON. Akin Savas Toklu, M.D.: The risk factors for DON are inadequate decompression, a history of bends, deep and Toldu: I am not aware of any published study on DON long dives, a high number of dives, older age, obesity and screening among technical divers,but prevalence is very low coagulation abnormalities. among military divers,who generally dive deep and conduct

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longer decompressions using mixed gas. Thus, it is possible to state that technical diving itself does not carry a higher risk of DON as long as decompression rules are strictly obeyed.

Gempp: Technical diving is theoretically regarded as a risky practice since divers are exposed to prolonged ongassing using or , which implies specific but often empirical decompression procedures. However, in the past five years only two nonmilitary, noncommercial divers using trimix were treated for musculoskeletal DCS in our hyperbaric center. In both cases screening for DON lesions was negative. There are many reasons for this discrepancy; principal among them is the small number of subjects.

Is there any justification for screening technical divers for DON?

Gempp: At present it is premature to impose systematic radiological investigations before determining (with future studies) the real prevalence of asymptomatic DON in this population. Detection of clotting-factor disorders that may contribute to the occurrence of DON is promising, but additional research is needed.

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