Intraarticular Rupture Pattern of the ACL Thore Zantop, MD * ; Peter U. Brucker, MD; Armando Vidal, MD; Boris A. Zelle, MD; and Freddie H. Fu, MD † To date, the intraarticular rupture pattern of the anterior cruciate ligament (ACL) has not been reported. The ACL is a complex structure consisting of two functionally synergistic structures: the anteromedial (AM) and posterolateral (PL) bundle. The purpose of our study was to evaluate the intra- articular rupture pattern of the ACL with regard to its two functional bundles. We examined ACL rupture patterns with regard to the integrity of AM and PL bundle in 121 consecu- tive patients undergoing anterior cruciate ligament recon- struction surgery within 120 days after injury. The intraar- ticular pattern was observed by one experienced surgeon. In 25% of the patients a partial rupture of the ACL was found, whereas in the remaining 75% a complete rupture of AM and PL bundles was seen. A partial rupture could only be detected by careful dissection of the ligament. In 44% of all patients the AM and PL bundles did not rupture at the same location. In 12% of the patients the PL bundle showed no signs of rupture. When performing ACL reconstruction, care should be taken when dissecting down the ACL rem- nants to evaluate intact fiber bundles of the ACL. Level of Evidence: Level IV, diagnostic study. See Guidelines for Authors for a complete description of levels of evidence. Isolated anterior cruciate ligament (ACL) injuries are one of the most frequent of all ligamentous injuries to the knee, and have been reported to occur in an estimated one in 3000 people in the general population in the US. 6,12,19,20 An estimated 75,000 to 100,000 ACL reconstructions are performed annually in the United States. 2,4,10,11 Conse- quently, the ACL has become one of the most frequently studied musculoskeletal structures. Although a vast amount of information has been published about different graft types, surgical techniques, and postoperative reha- bilitation protocols, the etiology of ACL injuries is still poorly understood. Investigators believe the complex anatomic structure of the ACL is divided into two functionally and biomechani- cally synergistic anatomic bundles (Fig 1). 9,16–18,21,23,25 A complete rupture of AM and PL bundles will lead to sub- stantially increased anterior tibial translation and internal tibial rotation, resulting in instability and giving way phe- nomenon for the patient. 3,8,18,21,22,25 The increased ante- rior tibial translation can be diagnosed using the Lachman test, whereas the rotational instability may be tested with the pivot shift test. 9,16–18,21,23,25 In the 1970s Furman et al 7 showed in their in vitro study a positive anterior drawer sign can only be obtained if the AM bundle is severed. While the importance of the two functional bundles is recognized, we are unaware of any study establishing the patterns of rupture. We therefore sought to establish the frequency of rup- ture of the individual bundles and the location of rupture in each. MATERIALS AND METHODS We prospectively observed the intraoperative rupture patterns of the ACL in 121 patients (75 male, 46 female). We included patients older than 14 years who were arthroscopically evaluated within 120 days after injury. Patients had to experience only one instability episode. We excluded patients with any recurrent sub- luxation episodes after the initial trauma, previous ACL surgery, and those with injuries older than 120 days. The mean age was 31.5 (± 9.7, SD) years. The patients had a mean weight and height of 69.0 (± 3.7) kg and 177.0 (± 35.4) cm, respectively. The mean body mass index (BMI) was 22.0 kg/m 2 . The mean interval between injury and evaluation of the rupture pattern was 50.7 days (± 28.5). The right knee was involved in 55 patients From the * Department of Trauma, Hand and Reconstructive Surgery, Wilhelms University Muenster, Germany; and the † Department of Ortho- paedic Surgery, University of Pittsburgh, Pittsburgh, PA. Each author certifies that he or she has no commercial associations (eg, consultancies, stock ownership, equity interest, patent/licensing arrange- ments, etc) that might pose a conflict of interest in connection with the submitted article. Each author certifies that his or her institution has approved the human protocol for this investigation and that all investigations were conducted in conformity with ethical principles of research, and that informed consent was obtained (IRB #0505139). Correspondence to: Thore Zantop, MD, Department of Trauma, Hand and Reconstructive Surgery, University of Muenster, Waldeyer Strasse 1, 48149 Muenster, Germany. Phone: 00149-251-8356301; Fax: 00149-251-8356318; E-mail: thore.zantop@ukmuenster.de. DOI: 10.1097/BLO.0b013e31802ca45b CLINICAL ORTHOPAEDICS AND RELATED RESEARCH Number 454, pp. 48–53 © 2007 Lippincott Williams & Wilkins 48 Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.