There is significant load sharing and physical interaction between the anteromedial and posterolateral bundles of the ovine ACL under anterior tibial loads

IntroductionThe ovine stifle joint is an ideal preclinical model to test the ability of double-bundle reconstruction techniques in providing superior joint stability and less osteoarthritis (OA) compared with single-bundle techniques. However, knowledge of the normal ovine ACL and more specifically the load sharing and physical interaction between the two main bundles of the ovine ACL is currently limited.MethodsSix ovine stifle joints were tested using a robotic testing system. Each joint was cyclically loaded to 200 N in the anterior tibial direction between 30° and 90° flexion and the force-displacement data were recorded for both the intact ACL, and when the anteromedial (AM, n = 3) or the posterolateral bundle (PL, n = 3) was transected.ResultsThe load shared by the AM bundle increased from 30° to 75° of flexion at all loading levels (25–200 N); whereas, the load shared by the PL bundle decreased between full extension and mid flexion (60°) and then increased again. The load borne by the AM bundle did not change in response to increasing Anterior Tibial Loads (ATL) at each flexion angle, in contrast to the PL bundle (P = 0.004). Physical interaction between bundles was greatest at 60° and under 50 N ATL.ConclusionThese data will help create double-bundle ACL reconstructions in sheep which are functionally similar to intact native ACL. In turn, this model can be used to examine the success of anatomically accurate double-bundle reconstructions to prevent the development of OA. Level of evidence: III.