Osteonecrosis is:
Avascular necrosis is a disease resulting from the temporary or permanent loss of the
blood supply to the bones.
[1] Without blood, the bone tissue dies and causes the bone to collapse.
[1] If the process involves the bones near a joint, it often leads to collapse of the joint surface. This disease also is known as
osteonecrosis,
aseptic (bone) necrosis, and
ischemic bone necrosis.
[1]
Contents
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Causes
There are many theories about what causes avascular necrosis. Proposed risk factors include
alcoholism[2], excessive
steroid use,
[3] post trauma,
[4][5] caisson disease (decompression sickness),
[6][7] vascular compression,
[8] hypertension,
vasculitis,
thrombosis, damage from
radiation,
bisphosphonates (particularly the
mandible),
[9] sickle cell anaemia,
[10] and
Gaucher's Disease.
[11] In some cases it is
idiopathic (no cause is found).
[12] Rheumatoid arthritis and lupus are also common causes of AVN.
Presentation
While it can, by definition, affect any bone, and half of cases show
multiple sites of damage, this disease primarily affects the joints at
the
shoulder,
knee, and
hip.
Although it can happen in any bone, avascular necrosis most commonly affects the ends (
epiphysis) of long bones such as the
femur, the bone extending from the knee joint to the hip joint. Other common sites include the
humerus (the bone of the upper arm),
[13][14] knees,
[15][16] shoulders,
[13][17] ankles and the
jaw.
[18] The disease may affect just one bone, more than one bone at the same time, or more than one bone at different times.
[19]
Avascular necrosis usually affects people between 30 and 50 years of
age; about 10,000 to 20,000 people develop avascular necrosis of the
head of the femur in the US each year. When it occurs in children at
the femoral head, it is known as
Legg-Calvé-Perthes syndrome.
[20]
Diagnosis
Orthopaedic doctors most often diagnose the disease except when it affects the
jaws, when it is usually diagnosed and treated by dental and maxillofacial surgeons.
Because early x-rays are usually normal in the early stage of the disease, bone scintigraphy
[21] and MRI
[22]
are the diagnostic modalities of choice since both can detect minimal
changes at early stages of the disease. Late radiographic signs include
a radiolucency area following the collapse of subchondral bone
(crescent sign) and ringed regions of radiodensity resulting from
saponification and calcification of marrow fat following medullary
infarcts.
Treatment
Avascular necrosis is especially common in the hip joint. A variety of methods are now used to treat avascular necrosis,
[19] the most common being the
total hip replacement,
or THR. However, THRs have a number of downsides including long
recovery times and short life spans. THRs are an effective means of
treatment in the geriatric population, however doctors shy away from
using them in younger patients due to the reasons above. A new, more
promising treatment is metal on metal (MOM) resurfacing. It is a form
of a THR, however in this procedure, only the head of the femur is
removed as opposed to a THR in which the entire neck is removed. MOM
resurfacing is still experimental in America but has been endorsed in
Great Britain as an excellent alternative to a THR. A MOM Resurfacing
may not be suitable in all cases of Avascular Necrosis, its suitability
depends on how much damage has occurred to the femoral head of the
patient, bone is always undergoing change or remodelling.
[23] The bone is broken down by osteoclasts and rebuilt by osteoblasts.
[23] Some doctors also prescribe
bisphosphonates (e.g.
alendronate) which reduces the rate of bone breakdown by osteoclasts, thus preventing collapse (specifically of the hip) due to AVN.
[24]
Other treatments include Core Decompression, where internal bone
pressure is relieved by drilling a hole into the bone, and living bone
chip and electrical device to stimulate new vascular growth are
implanted; and the Free Vascular Fibular Graft (FVFG), in which a
portion of the fibula, along with its blood supply, is removed and
transplanted into the femoral head.
[25]
Progression of the disease could be halted by transplanting
nucleated cells from bone marrow into avascular necrosis lesions after
core decompression, although more research is needed to establish this
technique.
[26][27]
Prognosis
The amount of disability that results from avascular necrosis
depends on what part of the bone is affected, how large an area is
involved, and how effectively the bone rebuilds itself. The process of
bone rebuilding takes place after an injury as well as during normal
growth.
[23]
Normally, bone continuously breaks down and rebuilds—old bone is
reabsorbed and replaced with new bone. The process keeps the skeleton
strong and helps it to maintain a balance of minerals.
[23]
In the course of avascular necrosis, however, the healing process is
usually ineffective and the bone tissues break down faster than the
body can repair them. If left untreated, the disease progresses, the
bone collapses,
[1] and the joint surface breaks down,
[12] leading to pain and arthritis.
[12]
Dude.... that sucks +k +vibes more on the bright side though, Brett Farve has it and dude is mothafuckin tank
