Three bones meet at the knee joint – the thigh bone (femur), the shin bone (tibia) and the knee cap (patella). The surfaces of these bones are all covered by a highly specialised layer of cartilage called articular cartilage – this surface is very smooth and slippery and allows the knee joint to move with minimal friction. Articular cartilage covers the surfaces of bones in all the moving joints throughout the body. The knee joint also has specialised meniscus cartilage structures (unique to the knee joint) that are quite different in shape and function to the articular cartilage. Please see the section titled Meniscus Injury for information about meniscus injury.
Articular cartilage can become injured or damaged. Cartilage injury could (and does) occur in any joint of the body but the knee joint is particularly prone to such injury. Articular cartilage injury can result from genuine trauma to the knee. It can also occur in young people (teenage years and below) due to a condition called “Osteochondritis Dissecans” (OCD for short) in which a segment of cartilage and the bone that it is attached to becomes soft and unstable. If left untreated, it can eventually break away from its normal location to become a loose fragment floating around the knee joint.
Articular cartilage injury, either due to an acute knee injury or due to osteochondritis dissecans can cause repeated episodes pain and swelling of the knee. Loose cartilage (and bone) fragments lying within the knee joint can cause locking of the knee.
Not all articular cartilage injuries of the knee require surgical treatment, however, in younger patients with otherwise healthy knees (no underlying arthritis) and injury to more important regions of cartilage (segments that are subjected to higher loads when weightbearing), then cartilage repair, transplantation or restoration surgery may be advisable. Please see the section titled Cartilage Transplantation and Restoration Surgery for details.