necrosis [bone death from lack of circulation]. Dive-
related factors associated with DON include the number of
lifetime dives, dive depths greater than 115 to 130 feet and
empirical decompression procedures. Diver-related factors
include previous musculoskeletal DCS (limb bends), older
age, excessive alcohol consumption, high cholesterol and
coagulation abnormalities. Some researchers suspect rapid
rates of compression and increased partial pressure of oxygen.
Mahito Kawashima, M.D., Ph.D.:
The main risk factor
is a history of musculoskeletal DCS. This was established
by many studies that screened divers for DON, and it was
confirmed by experimental studies with sheep. Inadequate
decompression is another big factor. Divers such as fishermen
who decompress empirically instead of following standard
decompression procedures are at high risk. Obese divers
should be careful, too.
Akin Savas Toklu, M.D.:
The risk factors for DON are
inadequate decompression, a history of bends, deep and
long dives, a high number of dives, older age, obesity and
coagulation abnormalities.
Are recreational divers at risk for DON?
Toklu:
Limited studies have shown that DON is not a significant
risk for recreational divers. The risk might increase with
violations of decompression rules and depth or time limits. The
decompression algorithms currently being used in recreational
diving are safe enough that DON is unlikely if there are no other
predisposing factors for osteonecrosis.
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 observed
in the past decade, but the few studies that attempted to
determine the prevalence of DON among recreational divers
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 experienced
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 the
first hyperbaric treatment might be a prognostic sign of DON
development. Since 2004 we have actively followed divers
who experienced musculoskeletal DCS. So far there are 33
divers in this cohort. It appears that being older than 40 and
experiencing delays to recompression of more than six hours
increase risk of DON. Our findings strongly suggest that
routine MRI examination is justified in recreational divers
treated for limb bends before they return to diving.
Kawashima:
Yes. Compared to technical divers, the number
of cases among recreational divers is much smaller, but some
cases are reported.
Does technical diving expose divers to a higher risk of DON?
Kawashima:
Yes. Deep divers, especially, are at high risk.
This was shown by a group screening of Japan Agency for
Marine-Earth Science and Technology (JAMSTEC) divers in
which three divers among 30 were found to have DON.
Toklu:
I am not aware of any published study on DON
screening among technical divers, but prevalence is very low
among military divers, who generally dive deep and conduct
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COURTESY TOM BALKANY, M.D.
BSIP/GETTY IMAGES
From top: Patient undergoing MRI; MRI of osteonecrosis in the hips