Degenerative joint disease (DJD) describes an osteo-arthritic condition of a joint, but refers more to the degeneration of the articular cartilage than to the bone. It can occur at any age because of ‘wear and tear’, previous trauma to any joint or just due to the natural ageing process.
As the cartilage ages, it starts to wear out and becomes damaged and the joint capsule may become swollen as more joint fluid is produced in an attempt to provide cells for repairing the damage. Unfortunately this fluid is of a much lower viscosity and of lesser quality than normal, due to the lower molecular weight of hyaluronic acid (responsible for reducing friction), this means less lubricating support for the joint and greater pressure on the articular cartilage causing pain. In the longer term, poor quality joint fluid reduces the nutrition for the cells of the articular cartilage.
Although all affected joints will have cartilage changes not all will have bony changes to begin with, but the presence of degenerating cartilage within a joint means the joint fluid remains of a poor quality and so the cartilage does not heal.
Eventually bony changes develop in the form of new bone being formed, changes in the shape of the bone, or changes in the density and internal structure of the bone.
Treatment by corticosteroids is used as a ‘quick fix’ but is controversial as this inhibits cartilage healing, weakens all adjacent tissue and lowers resistance to infection. Also, corticosteroids melt cartilage and can lead to joint inflexibility and breakdown. Injections of hyaluronic acid, or its sodium salt, sodium hyaluronate, either directly into the joint or intravenously can result in long term improvement by restoring the viscosity of synovial fluid. Taking joint fluid from a healthy joint and injecting it into the DJD joint will have a similar effect.