Joint Surface Injures
The articular cartilage may be damaged after a jarring or twisting injury of the knee. It may also occur in conjunction with meniscus and ligament injury. The result can be a loose fragment of articular cartilage which leaves an exposed area of bone in the knee (a crater in the otherwise smooth joint surface). Alternatively the damage may be a breaking up or splitting, but not complete loss of, the articular cartilage.
In younger patients, this will usually result from a clear injury when there is a shearing or impaction force between the two surfaces. As we get older the articular cartilage becomes more degenerate and fragile, so injuries occur more easily (similarly for tears of the meniscus cartilage). In these cases there seems to be an overlap with the early beginnings of osteoarthritis.
Joint surface injury can be a potentially troublesome condition, particularly in young adults, because it may give rise to long term problems. It has been known for many years that articular cartilage does not heal well. If the meniscus is also torn, the prognosis is worse. It can be difficult to treat, and can increase the risk of developing significant osteoarthritis