Cartilage damage is relatively common and often occurs due to trauma or an associated medical condition. The most common cases of cartilage damage occur in the knee. Cartilage covers the surfaces of joints and functions as a shock absorber and prevents friction during movement. Unlike other tissues it has a poor blood supply which can affect its ability to heal. If arthroscopic (key-hole) surgery is recommended, it is often advisable to strengthen the muscles around the joint before the date of surgery, as this will speed up the recovery time after surgery.