Arthrodesis, also known as artificial ankylosis or syndesis, is the artificial induction of joint ossification between two bones via surgery. This is done to relieve intractable pain in a joint which cannot be managed by pain medication, splints, or other normally-indicated treatments. The typical causes of such pain are fractures which disrupt the joint, and arthritis. It is most commonly performed on joints in the spine, hand, ankle, and foot. Historically, knee and hip arthrodeses were also performed as pain relieving procedures, however with the great successes achieved in hip and knee arthroplasty, arthrodesis of these large joints has fallen out of favour as a primary procedure, and now are only used as procedures of last-resort in some failed arthroplasties.

It can be done in several ways:

• A bone graft can be created between the two bones using a bone from elsewhere in the person's body (autograft) or using donor bone (allograft) from a bone bank.
  • Bone autograft is generally preferred by surgeons because, as well as eliminating the risks associated with allografts, bone autograft contains native bone-forming cells (osteoblasts), so the graft actually forms new bone itself (osteoinductive), as well as acting as a matrix or scaffold to new bone growing from the bones being bridged (osteoconductive). The main drawback of bone autograft is the limited supply available for harvest.
  • Bone allograft has the advantage of being available in far larger quantities than autograft; however, the treatment process the bone goes through following harvest, which usually involves irradiation and deep-freezing, kills the bone forming cells. This significantly reduces the immunogenicity (risk of graft rejection) such that no anti rejection drugs are needed. The process also makes the allograft function only as an osteoconductive matrix.
• A variety of synthetic bone substitutes are commercially available. These are usually hydroxyapatite based granules formed into a coralline or trabecular structure to mimic the structure of cancellous bone. They act solely as an osteoconductive matrix. Some manufacturers have recently begun supplying these products with soluble bone-forming factors such as bone morphogenetic protein to attempt to create a synthetic product with osteoinductive properties.
• Metal implants can be attached to the two bones to hold them together in a position which favors bone growth.
• A combination of the above methods is also commonly employed to facilitate bony fusion.

At the completion of surgery and healing, which takes place over a period of several months to over a year, the two adjoining bones are fused and no motion takes place between them. This can have the effect of actually strengthening the bones, as in anterior cervical fusion.

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