A middle aged man gets up with a hand on his knee and starts walking - each step full of pain. An old lady walks on the road with sideways swinging of upper body to compensate for stiff knees. These are some of the familiar sights we encounter daily and are due to Osteoarthritis of knees, the joints most commonly affected by this disease.
Osteoarthritis (OA) is a common type of arthritis seen in human beings. OA can be identified in knees of 35% of people as early as age 30. It is the second leading cause of disability in those over 50 years and it becomes almost universal in persons over 50. At least 85% of persons aged 70 to 79 years have diagnosable OA. OA can be either idiopathic (of unknown cause) or secondary - following injury, in other bone and joint disorders e.g. Rheumatoid arthritis or associated with obesity.
Normally a joint is formed by articular capsule, hyaline cartilage, synovial membrane and synovial fluid. The cartilage acts like a sponge and a shock absorber and synovial fluid squeezes out of it when under pressure. The cartilage reabsorbs synovial fluid when pressure is removed. That is why the height of human beings is three quarters of an inch shorter at night than in the morning. Synovial fluid is the best lubricant that science knows. Thus it makes the surface of the cartilage almost frictionless! The coefficient of friction is about that of an ice skate on ice or an ice to ice surface. When studied by engineers it is found to be 4 times more slippery than Teflon, the most slippery material man has ever made!
Such a marvel of nature stops functioning properly due to malfunction of chondrocytes, the cells responsible for repair of cartilage. This may follow a change in the microenvironment of articular cartilage or due to inflammation caused by repeated stress.
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