Joints are covered by a cartilage tissue which facilitates joint movement. The joint cartilage may be injured as a result of inappropriate movements or impact on the joints. Damaged areas called chondral lesions appear as a result of such injuries. Pieces broken down from the cartilage may obstruct the joint and prevent movement. Pieces are removed by arthroscopic methods or the condition is treated by cartilage transplantation (mosaicplasty).