Arthroscopy constitutes an important supplementary method for investigating and diagnosing affections of the knee joint. Despite the low risk and little trouble it causes to the patient it should only be used if radiological and repeated clinical examinations do not permit any evaluation of the disease. Arthroscopy is the method of choice in case of cartilage damage because from the appearance of the altered cartilage conclusions may be drawn about the occurrence and kind of the trauma. This examination method is valuable not only in diagnosis, it is also used to follow up the result of surgical interventions. Small pieces of cartilage that cannot be fixed may be removed by means of the arthroscope, so that examination and therapy can be done in one single operation. In most cases, cartilage damage is caused by laxity of ligaments.