Osteoarthritis Pathology

Osteoarthritis pathology starts in the cartilage and gradually involves the whole of the joint. Initially cracks develop on the surface of the cartilage and it becomes irregular. Gradually these cracks get deeper and wider and erode a portion of the joint cartilage. This occurs in some places whereas others areas of cartilage remain uninvolved.

Microscopically chondrocytes multiply and gather in clusters near the areas of cartilage damage. These cells under the influence of certain certain molecules that regulate the inflammatory process called cytokines and growth factors release enzymes that further breakdown the matrix of the cartilage. Due to this the tight binding of the negatively charged molecules becomes loose and now cartilage is no longer able to withstand compressive forces and wears down quicker.

Under the effect of cytokines the cells of the bone called osteocytes just underneath the cartilage become active and cause the bone to become thickened and stiff.

Near the areas of cartilage loss chondrocytes also attempt to form new cartilage. This new cartilage is not organised and under the influence of cytokines gets vascularized. Blood vessels bring calcium that gets deposited in this cartilage and now it is converted to bone. This bone is seen in the form of outgrowths called osteophytes. These can be seen of x rays and are helpful in diagnosis. Osteophytes develop at the site of maximum cartilage loss.

Under the influence of cytokines and growth factors the synovial tissue becomes inflamed. Number of cell in the synovium increase and the amount of synovial fluid also increases. Enzymes are released in the synovial fluid which attempt to digest chips of loose cartilage. At times the synovium may remain normal and not undergo these changes.

Swelling and deformity can produce stretching of ligaments making the joint unstable and more vulnerable to injury. Pain causes the patient to avoid activity this leads to weakening of the muscles. These weak muscles are unable to support the joint efficiently leading to more damage.

Thus can see that cartilage breakdown and inflammation leads to weakening of joint protectors which leads to further cartilage breakdown and producing a vicious cycle that causes rapid progression of the disease.

This page was last updated on 10 th June 2009

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