Dysbaric osteonecrosis
Encyclopedia
Dysbaric osteonecrosis or DON is a form of avascular necrosis
where there is death of a portion of the bone
that is thought to be caused by nitrogen
embolism
(blockage of the blood vessels by a bubble of nitrogen coming out of solution) in divers. Although the definitive pathologic process is poorly understood, there are several hypotheses:
is made by x-ray
/MRI appearance and has five juxta-articular classifications and forehead, neck, and shaft classifications indicating early radiological signs.
Early on there is flattening of articular surfaces, thinning of cartilage
with osteophyte (spur) formation. In juxta-articular lesions without symptoms, there is dead bone and marrow separated from living bone by a line of dense collagen. Microscopic cyst
s form, fill with necrotic material and there is massive necrosis with replacement by cancellous bone with collapse of the lesions.
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).
The following staging system is sometimes useful when managing lesions.
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).
Worsening of the condition from continued decompression in an asymptomatic x-ray finding may occur.
Its relationship to compressed air is strong in that it may follow a single exposure to compressed air, may occur with no history of DCS but is usually associated with significant compressed air exposure. The distribution of lesions differs with the type of exposure - the juxta-articular lesions being more common in caisson workers than in divers.
There is a definite relationship between length of time exposed to extreme depths and the percentage of divers with bone lesions.
. Cancellous bone grafts are of little help.
(DCS) with recompression and hyperbaric oxygen also reduce the risk of subsequent DON.
There is the potential for worsening of DON for any diving where there might be a need for decompression, experimental or helium
diving. 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. These risks are affected by the degree of disability, and the type of lesion; juxtaarticular or shaft.
Avascular necrosis
Avascular necrosis is a disease where there is cellular death of bone components due to interruption of the blood supply. Without blood, the bone tissue dies and the bone collapses...
where there is death of a portion of the bone
Bone
Bones are rigid organs that constitute part of the endoskeleton of vertebrates. They support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue...
that is thought to be caused by nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
embolism
Embolism
In medicine, an embolism is the event of lodging of an embolus into a narrow capillary vessel of an arterial bed which causes a blockage in a distant part of the body.Embolization is...
(blockage of the blood vessels by a bubble of nitrogen coming out of solution) in divers. Although the definitive pathologic process is poorly understood, there are several hypotheses:
- Intra- or extravascular nitrogen in bones, "nitrogen embolism".
- Osmotic gas effects due to intramedullary pressure effects.
- fat embolism
- hemoconcentration and increased coagulability.
Process
The diagnosisMedical diagnosis
Medical diagnosis refers both to the process of attempting to determine or identify a possible disease or disorder , and to the opinion reached by this process...
is made by x-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
/MRI appearance and has five juxta-articular classifications and forehead, neck, and shaft classifications indicating early radiological signs.
Early on there is flattening of articular surfaces, thinning of cartilage
Cartilage
Cartilage is a flexible connective tissue found in many areas in the bodies of humans and other animals, including the joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs...
with osteophyte (spur) formation. In juxta-articular lesions without symptoms, there is dead bone and marrow separated from living bone by a line of dense collagen. Microscopic cyst
Cyst
A cyst is a closed sac, having a distinct membrane and division on the nearby tissue. It may contain air, fluids, or semi-solid material. A collection of pus is called an abscess, not a cyst. Once formed, a cyst could go away on its own or may have to be removed through surgery.- Locations :* Acne...
s form, fill with necrotic material and there is massive necrosis with replacement by cancellous bone with collapse of the lesions.
The lesion
Lesion
A lesion is any abnormality in the tissue of an organism , usually caused by disease or trauma. Lesion is derived from the Latin word laesio which means injury.- Types :...
begins as a random finding on x-ray without symptoms. Symptomatic lesions usually involve joint surfaces and fracture
Fracture
A fracture is the separation of an object or material into two, or more, pieces under the action of stress.The word fracture is often applied to bones of living creatures , or to crystals or crystalline materials, such as gemstones or metal...
with attempted healing occurs. This process takes place over months to years and eventually causes disabling arthritis
Arthritis
Arthritis is a form of joint disorder that involves inflammation of one or more joints....
, particularly of the femoral head (hip).
The following staging system is sometimes useful when managing lesions.
- Stage 0 - Intravascular coagulationCoagulationCoagulation is a complex process by which blood forms clots. It is an important part of hemostasis, the cessation of blood loss from a damaged vessel, wherein a damaged blood vessel wall is covered by a platelet and fibrin-containing clot to stop bleeding and begin repair of the damaged vessel...
- Stage 1 - Dead Bone without repair
- Stage 2 - Dead Bone with repair but without collapse
- Stage 3 - Dead Bone with repair and with collapse
- Stage 4 - Secondary degenerative arthritisArthritisArthritis is a form of joint disorder that involves inflammation of one or more joints....
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).
Worsening of the condition from continued decompression in an asymptomatic x-ray finding may occur.
Prevalence
Dysbaric osteonecrosis is a significant occupational hazard, occurring in 50% of commercial Japanese divers, 65% of Hawaiian fishermen and 16% of commercial and caisson divers in the UK.Its relationship to compressed air is strong in that it may follow a single exposure to compressed air, may occur with no history of DCS but is usually associated with significant compressed air exposure. The distribution of lesions differs with the type of exposure - the juxta-articular lesions being more common in caisson workers than in divers.
There is a definite relationship between length of time exposed to extreme depths and the percentage of divers with bone lesions.
Treatment
Treatment is difficult, 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 femurFemur
The femur , or thigh bone, is the most proximal bone of the leg in tetrapod vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in...
. Cancellous bone grafts are of little help.
Prevention
Prevention is a more successful strategy than treatment. By using the safest decompression table possible, the risk of DON is reduced. Prompt treatment of any symptoms of decompression sicknessDecompression sickness
Decompression sickness describes a condition arising from dissolved gases coming out of solution into bubbles inside the body on depressurization...
(DCS) with recompression and hyperbaric oxygen also reduce the risk of subsequent DON.
Prognosis
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. Divers who have suffered from DON are at increased risk of future fracture of a juxta-articular lesion during a dive, and may face complications with future joint replacements. Because of the young age of the population normally affected, little data is available regarding joint replacement complications.There is the potential for worsening of DON for any diving where there might be a need for decompression, experimental or helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...
diving. 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. These risks are affected by the degree of disability, and the type of lesion; juxtaarticular or shaft.