As the saying goes, “old age comes before old legs.” We often hear complaints from older people about sore knees, inability to walk long distances, difficulty walking up and down stairs, difficulty walking, or even inability to walk on their own, which often indicate possible osteoarthritis. Osteoarthritis is a chronic joint disease characterized by degeneration of joint cartilage and secondary osteophytes. Pain, swelling and increasing mobility impairment of the joints are the three major manifestations of osteoarthritis. Understanding the early manifestations of the disease, paying attention to them, and taking measures can effectively prevent mobility problems and possible disability in the later stages. Osteoarthritis can be classified as mild, moderate or severe depending on the severity of the disease. Mild: Usually mild or moderate intermittent vague pain in the joints that improves with rest and worsens with activity. The stiffness and tightness of the joints when waking up in the morning, also known as “morning stiffness”, can be relieved after activity, and joint movement is basically unaffected at this stage, but there is a bit of “leg weakness”. Moderate: As the disease progresses, the pain can gradually increase, and the pain cannot be relieved when resting. Normal walking, walking up and down stairs, squatting and standing are significantly affected. Severe: redness and swelling of the joint, fever, increased pain, persistent pain, and no relief at night. The joint is swollen and deformed due to the formation of bony bulge or joint effusion and joint destruction, and walking on flat ground is also difficult or even completely impossible. Why does osteoarthritis occur? It starts with the structure and function of the joint. The joint consists of the joint head, articular cartilage, and joint capsule. The joint head is the basic structure of the joint. The articular cartilage is smooth, flexible and tough, and covers the surface of the joint head, which is the direct contact part for sliding and friction, while the joint capsule is a dense fibrous tissue that plays a wrapping role. The articular cartilage and synovial membrane continuously secrete synovial fluid, which nourishes the articular cartilage and serves as a lubricant. Outside the joint, there are ligaments and muscles that strengthen and stabilize the joint. Joints are subjected to constant movement and pressure, and sliding friction occurs, so the proper functioning of joints must be supported by strong bones, smooth and flat cartilage as the contact surface, and normal synovial fluid as lubrication. In fact, the coefficient of friction between normal joint cartilage is less than that of an ice skate sliding on an ice surface. The importance of synovial fluid Tips In the normal joint cavity, there exists a small amount of synovial fluid, which is secreted by synovial cells of the synovial membrane, chondrocytes, and is composed mainly of water, sodium vitreous acid, nutrients, immune proteins and a small amount of cells. Synovial fluid can penetrate into cartilage, tendons and other tissues. Normal synovial fluid is clear, viscous, silky and flexible, and plays the role of lubricating joints and buffering mechanical pressure and friction in joints. Since there are no blood vessels in cartilage, synovial fluid also plays the role of nourishing cartilage, diluting and discharging cartilage metabolites. In old age, synovial fluid secretion also begins to decrease and become thin, and the lubricating and nutritive effects on the joints begin to deteriorate. In severe cases of osteoarthritis, the joints are stimulated for a long time, and the secretion of synovial fluid will increase a lot, but the composition will change, and the inflammatory component will increase, becoming thin and cloudy, and the joint fluid at this time will not only fail to play the role of lubrication and nutrition, but also cause damage to the joints, which is called joint effusion. As the body ages and the joints are overused, the result is that the joint head is no longer strong and deformed, or the joint cartilage is worn and broken, and the composition of the joint fluid changes so that it can no longer play a good role in lubrication and nutrition, and the joints become painful, impaired in movement and swollen. osteophytes” and “bone spurs”), exuding inflammatory fluid and further aggravating the damage and destruction of joint cartilage and bursae. Osteoarthritis can occur in the following two ways: Primary Most often occurs in middle-aged and elderly people, with no clear systemic or local cause, mostly due to aging of the body. Secondary Most often occurs in young adults and can be secondary to trauma, inflammation, uneven joint stress due to joint deformity, and chronic and repetitive cumulative strain injury.