The purpose of our study was to assess the ability of MR imaging to detect partial tears of the anterior cruciate ligament (ACL) as these injuries, if extensive enough, may result in ligamentous insufficiency or predispose to subsequent acquired knee instability.A review of all arthroscopic reports from two institutions during the periods 1990-1992 and 1992-1993, respectively, revealed 13 patients with partial tears of the ACL. Thirteen cases each of intact and completely ruptured anterior cruciate ligaments on arthroscopy were randomly selected as controls from the same report review. Preoperative MR images for all cases selected were obtained. Criteria for diagnosis included the absence of findings of complete ACL tear in conjunction with abnormal intrasubstance signal, bowing of the ACL, or nonvisualization of the ACL on one MR imaging sequence with visualization of intact fibers on other sequences. Inter- and intraobserver agreement was assessed using the kappa statistic.The sensitivity of MR imaging ...