From December 1981 to August 1986, arthroscopic meniscectomy of 147 joints in 139 cases was performed (medial normal type: 59, lateral normal type: 33, lateral complete discoid: 49, lateral imcomplete discoid: 52). Thirty-four cases of 58 normal type medial meniscus injury (58.6%) had no obvious history of trauma prior to the onset of symptoms. The most frequent configuration of the tear was longitudinal tear on lateral menscus and posterior flap tear on medial meniscus. Normal type meciscus injury with no history of trauma may be based on a degenerative aging process, but this injury was observed in younger people who were not involved in osteoarthritic changes of articular cartilage. This posterior type of tear had resemblance to the degenerative tear of posterior segment in osteoarthritis and was thought to be one of eary stage of medial type osteoarthritis.
