Article: Aseptic bone necrosis

Aseptic bone necrosis (ABN), also called avascular necrosis or osteonecrosis, is where bone and marrow die in the absence of an infective agent. It can affect any bone, and half of cases show multiple sites of damage, but primarily affects the joints at the shoulder, knee, and hip.

The condition shows necrosis anywhere in the bone. Damage within the length of the bone is usually asymptomatic. Necrosis in the epiphysis or in the bone joints, which extends into adjacent cartilage is more serious. All dead bone cells are eventually reabsorbed and replaced. But new bone is soft, may misshape or fracture under pressure producing malformed joint surfaces and hence pain and mobility problems, afflictions such as arthritis. These joints must be treated surgically, by replacement.

It can be caused by a number of conditions that damage bone cells, including fractures, vascular compression, hypertension, vasculitis, thrombosis, the use of corticosteroids, and damage from radiation.

It can also be found in divers, around 5% of professional divers develop ABN, as a consequence of inadequate decompression. Such decompression may be sufficient to prevent decompression sickness, but produces nitrogen bubbles that block blood circulation in some bone areas. A famous non-diving sports person with this condition is cyclist Floyd Landis, one of the top contenders for the 2006 Tour de France.

Avascular necrosis is especially common in the hip joint. A variety of methods are now used to treat avascular necrosis, 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 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. Metal on metal resurfacing is still experimental in America but has been endorsed in Great Britain as an excellent alternative to a THR. Some doctors also prescribe medicines such as Fosamax which are believed to increase the rate at which new bone replaces the dead bone, thus preventing collapse (specifically of the hip) due to AVN.

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