Problem -- Osteonecrosis
Dysbaric osteonecrosis is the death of a portion of
the bone that is thought to be caused by nitrogen
embolization "blockage" of the blood vessels in divers. Although the
definitive
pathologic process is poorly understood, there are several hypotheses:
- Intra- or extravascular nitrogen in bones, "nitrogen
embolization".
- Osmotic gas effects due to intramedullary pressure effects.
- fat embolization
- hemoconcentration and increased coagulability.
The lesion begins as a random finding on x-ray without symptoms.
Symptomatic
lesions usually involve joint surfaces and fracture with attempted
healing
occurs. This process takes place over months to years and eventually
causes
disabling arthritis, particularly of the femoral head (hip).
In a study of bone lesions in 281 compressed air workers done by
Walder in 1969, 29% of the lesions were in the humeral head (shoulder),
16% in the femoral head (hip), 40% in the lower end of the femur(lower
thigh at the knee) and 15% in the upper tibia (knee below the knee cap).
Diving Concerns
---Condition Related
Worsening of the condition from continued decompression in an
asymptomatic x-ray finding may occur.
---Treatment Related
The treatment is less than successful, often
requiring a joint replacement.
Spontaneous improvement occasionally happens and some juxta-articular
lesions
don't progress to collapse. Other treatments include immobilization and
osteotomy of the femur. Diving would be precluded during active
treatment and rehabilitation.
The best treatment is prevention by using the safest
decompression
table possible. Because of the high relationship with DCS, all DCS
symptoms
should be treated with Recompression and HBO.
---Diver Related
If the diver has not been exposed to excessive depth and decompression
and presents as DON, there may be a predisposition for the condition.
Diving should be restricted to shallow depths.
Diving Risk Assessment
---Risk from the Condition
---Fracture of a juxta-articular lesion during a dive.
---Risks from the Treatment
---Failure of various modalities
---Unknown long term outlook for joint replacements in the younger
population usually affected by DON
---Risks to the Diver
---Worsening of the condition by continued diving
Advising the Diver
---Potential for injury from future diving
There is the potential for worsening of dysbaric osteonecrosis for any
diving where there might be a need for decompression, experimental or
helium diving.
---Modifiers
--Degree of disability [Staging}
--Type of lesion; juxtaarticular or shaft
--Findings on studies and degree of benefit from treatment as determined
by studies.
--Need to dive; recreational, work related.
Dive or not dive
Physically stressful diving should probably be restricted, both in
sport diving and work diving due to the possibility of unnecessary
stress to the joint. Any diving should be less than 40 feet/12 meters.
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