bone, joint, and muscle disorders
Osteoarthritis (OA)
Causes of Osteoarthritis
Normally, cartilage reduces the friction level in joints and protects them from wearing out, even after years of typical use, overuse, or injury. Osteoarthritis is caused most often by tissue damage. In an attempt to repair a damaged joint, chemicals accumulate in the joint and increase the production of the components of cartilage, such as collagen (a tough, fibrous protein in connective tissue) and proteoglycans (substances that provide resilience). Next, the cartilage may swell because of water retention, become soft, start to breakdown, and then develop cracks on the surface. Tiny cavities form in the bone beneath the cartilage, weakening the bone. The attempt of the tissues to repair the damage may lead to new growth of bone and other tissue. Bone can overgrow at the edges of the joint, causing bumps (osteophytes) that can be seen and felt. Ultimately, the smooth, slippery surface of the cartilage becomes rough and pitted, so that the joint can no longer move smoothly and absorb impact. All the components of the joint—bone, joint capsule (tissues that enclose most joints), synovial tissue (tissue lining the joint cavity), tendons, ligaments, and cartilage—fail in various ways, thus altering the function of the joint. 