Osteoarthritis Develops in the Operated Joint of an Ovine Model following ACL Reconstruction with Immediate Anatomic Reattachment of the Native ACL Etienne J.O. O’Brien, 1 Jillian E. Beveridge, 1 Kyla D. Huebner, 1 Bryan J. Heard, 1 Janet E. Tapper, 1 Nigel G. Shrive, 1,2 Cyril B. Frank 1 1 Faculty of Medicine, The McCaig Institute for Bone & Joint Health, University of Calgary, Calgary, 3330 Hospital Drive NW, Alberta, Canada T2N 4N1, 2 Department of Civil Engineering, Schulich School of Engineering, University of Calgary, Calgary, Alberta, Canada Received 5 January 2012; accepted 18 June 2012 Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/jor.22187 ABSTRACT: We tested the hypothesis that immediate reattachment of the native anterior cruciate ligament (ACL) can prevent kine- matic changes and the development of osteoarthritis (OA). Five sheep underwent anatomic unilateral ACL reconstruction (ACL-R). Animals from a previous study served as sham (n ¼ 7) or non-operated (n ¼ 17) controls. At 4 points of walking gait, 6 degrees of freedom stifle joint kinematics of ACL-R animals were compared with sham controls at 4 and 20 weeks post-surgery. Gross cartilage, bone, and meniscal changes were graded at euthanasia; paired and differential scores were compared. Inter-animal differences were noted in all groups. Of 48 points of gait comparison between ACL-R and sham operated groups, 42 points showed no difference (p > 0.05). Of the six significant differences (p < 0.05), internal rotation in ACL-R animals accounted for three. At 20 weeks, differen- tial scores showed that sham operated joints were morphologically indistinguishable from non-operated controls (p  0.129) while ACL- R joints had significantly higher combined cartilage and osteophyte scores than those controls (p  0.003). This method of ACL recon- struction in sheep did not restore normal walking gait kinematics completely and allowed some OA to develop in operated joints. OA may result from relatively subtle mechanical abnormalities, apparently more so in some individuals than others. ß 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res Keywords: osteoarthritis; ACL reconstruction; kinematics; ovine stifle The premature development of osteoarthritis (OA) fol- lowing anterior cruciate ligament (ACL) reconstruction remains a common clinical problem. 1 Much clinical ev- idence exists that normal joint stability may not be ful- ly restored after all ACL reconstructions, 2 which could explain some of the incidence of OA. 2 Technical refine- ments, in particular the use of double bundle techni- ques, have been designed to improve post-operative joint kinematics and therefore reduce the occurrence of OA. However, it has yet to be demonstrated that these newer approaches to more anatomic replacement of the ACL actually achieve that goal. 1 Animal models provide a method of isolating and defining the causes of OA and any potential role(s) of mechanical abnormalities in OA development. Ovine stifle joints develop OA following isolated ACL injury 3 and are large enough to enable quantification of joint kinematics. 4 For example, in a combined ACL/medial collateral ligament injury (ACL/MCL Tx) model, we showed a potential correlation between changes in the medial/lateral degree of freedom and gross bone and cartilage changes. 5 To investigate the potential mechanisms of OA fol- lowing ACL injury and reconstruction more specifically, here we have created a model of ACL reconstruction in which the native ACL is cored out at one end and imme- diately replaced as anatomically as possible. 6 This model simulates a number of features of human ACL recon- structive surgery, including bone drilling and graft re- attachment. The model eliminates some confounding factors such as variation in graft attachment site and the use of non-ligamentous graft material that may have different mechanical properties to the native ACL. Our speculation was that an anatomically normal ACL, replaced immediately in its original location, has the greatest likelihood of any graft in restoring normal joint function without inducing OA. Our aims, therefore, were to evaluate the functional stability of joints during walking on a level treadmill, up to 20 weeks following this ideal ACL reconstruction compared with sham surgery, and to perform gross ex- amination of these joints for evidence of early OA. We hypothesized that following idealized reconstruction, like after sham surgery, joint kinematics during walk- ing would be unchanged. Further, we hypothesized that no gross evidence of OA would be found in recon- structed or sham operated joints compared with non- operated age matched controls at this early interval after surgery. METHODS All animal procedures followed protocols approved by the University of Calgary Health Sciences Animal Care Commit- tee and complied with guidelines from the Canadian Council on Animal Care. Twenty-nine adult (3–4 years old) female Suffolk-cross sheep were included. Surgical Procedures Each animal allocated to a surgical group had a modified fracture plate fitted to both the femur and tibia to allow attachment of a rigid marker system on the occasions of Additional supporting information may be found in the online version of this article. Grant sponsor: Canadian Institutes of Health Research and Alberta Innovates Health Solutions. Correspondence to: Cyril B. Frank (T: 403-220-6881; F: 403-283- 7742; E-mail: cfrank@ucalgary.ca) ß 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. JOURNAL OF ORTHOPAEDIC RESEARCH MONTH 2012 1