Knee arthritis is particularly common. It occurs when the knee presents pain, stiffness and inflammation. This disease may difficult to do many of the daily activities such as walking or climbing stairs. It is a major cause of lost work time and a serious disability for many older people although it can also affect young people and children.
The knee is the largest and strongest joint in your body. It has three parts: the lower end of the femur also called „thighbone“, the upper end of the tibia, also known as „shinbone“, and the patella or „kneecap“. The ends of the three bones (where they touch eachother) are covered with articular cartilage, which is a smooth, slippery substance that protects and cushions the bones so that the knee can be bent and straightened. The meniscus, which are two wedge-shaped pieces of cartilage, act as shock absorbers between the thighbone and shinbone. Meniscus are tough and rubbery in order to help cushion the joint and keep it stable. The synovial membrane is a thin lining that surrounds the knee joint and is in charge of releasing a fluid that lubricates the cartilage and reduces friction.
The knee can be affected by three types of arthritis: osteoarthritis, rheumatoid arthritis, and posttraumatic arthritis. Osteoarthritis is the most common form of arthritis that affects the knee. The cartilage in the knee joint gradually wears away, becomes frayed and rough, and the protective space between the bones decreases. As a consequence, the bones start rubbing together and the protective space between the bones decreases. This condition develops slowly and it causes painful bone spurs, which gets worse over time. Therefore osteoarthritis, is categorized as a degenerative type of arthritis (also called „wear and tear“) and it generally happens to most people over 50 years old but it can be also present in younger people. The second type of arthritis affecting the knee (and other joints too) is called rheumatoid arthritis. This illness is a chronic disease, which usually damages the joint on both sides of the body. This condition is caused when the synovial membrane that covers the knee joint starts to swell resulting in knee pain and stiffness. Since rheumatoid arthritis is an autoimmune disease, the healthy tissue such as cartilage and ligaments is damaged by the immune system and bones softening is the consequence. The third type of knee arthritis is known as Posttraumatic Arthritis. This is developed after a knee injury. It may happen when the broken bone damages the joint surface and leads to arthritis even years after the injury. Moreover, the meniscus may be teared and ligaments can be injured causing instability and additional wear on the knee joint, so that arthritis may result over time too.