Bone fragments formed within the joint and its periarticular rim are often the result of an abnormal proliferation of bone in response to excessive repair by mechanical action. Most of the bone growths do not need to be removed surgically, but only if the growths cause joint impingement symptoms, or if they lead to restricted joint movement, or if they irritate the joint ligaments and cause pain, the bone growths should be removed. For example, if an enlarged bone in the intercondylar fossa of the knee joint interferes with knee extension, it should be removed; if a highly unstable bone on the patella irritates the quadriceps tendon and causes pain, it should be considered for removal; if a bone in the lateral collateral ligament or anterior cruciate ligament causes impingement, it should be removed.