Cartilage damage
A joint is the meeting point of two bones to allow movement. Cartilage is the firm cushion found between the two bones to stop them from grating against each other.
A joint is wrapped inside a tough capsule that is filled with synovial fluid. This fluid lubricates the joint and keeps it moving smoothly. In osteoarthritis, the cartilage becomes brittle and splits. Some pieces of cartilage may even break away and float around inside the synovial fluid. This can lead to inflammation. Eventually, the cartilage can break down so much that it no longer cushions the two bones.
In the knee the joint is bolstered on both sides by additional strips of cartilage, called 'menisci' or semilunar cartilages. One of the most common knee injuries is a torn or split meniscus. Severe impact or twisting, especially during weight bearing exercise, can tear this cartilage. Tears of the meniscus can also occur in older people due to wear and tear. Symptoms include swelling, pain and the inability to straighten the leg. The damaged cartilage can be surgically trimmed or even removed without causing any joint instability.