Femoral Tunnel “Blowout” During ACL Reconstruction: A Biomechanical Analysis (SS-65)

Abstract

Introduction Suspensory femoral fixation is commonly used for soft-tissue graft ACL reconstruction. For this fixation to be utilized, it is considered imperative that the lateral femoral cortex is not violated. Anatomic, single and double-bundle femoral tunnel techniques lead to shorter tunnels and, thus, are susceptible to an increased incidence of cortical breaching, or “blowout.” When this occurs, it is assumed a secondary type of fixation is needed. The purpose of our study was to determine if secondary fixation is needed when femoral “blowout” occurs, and whether the diameter of the femoral tunnel affects the cyclical and ultimate load to failure of three different suspensory fixation devices. Methods Sixty fresh-frozen porcine femora were dissected to isolate the ACL footprint. Femoral ACL tunnels were then drilled at 7-, 8-, 9-, and 10-mm diameters. Biomechanical testing, both cyclical and load to failure, were undertaken utilizing an MTS machine. Five separate trials at each tunnel diameter were conducted for three different cortical suspension devices. Statistical analysis was then performed to compare the methods of failures and forces to failure across the four tunnel diameters, as well as the three devices. Results Mean load-to-failure decreased as the tunnel size enlarged for all three devices. In 7-mm tunnels, mean load-to-failure ranged from 1163.7 to 1455.0 N; in 8-mm tunnels, 1154.7 to 1643.2 N; in 9-mm tunnels, 820.8 to 1125.21 N; and in 10-mm tunnels, 314.7 to 917.8 N, across the three devices. No significant difference was seen with the mean load-to-failure between the three devices (p Conclusion When using suspensory fixation, secondary fixation is not always needed when the lateral cortex has been breached. With 7-mm and 8-mm diameter tunnels, failure loads with each of the suspensory devices tested, exceeded that of documented interference screw load to failure (an accepted means of soft tissue fixation) by at least 25%. In pediatric and double-bundle ACL reconstructions where smaller and shorter tunnels are routinely used, purposely breaching the lateral cortex when using suspensory fixation, is an acceptable technique to optimize tunnel length, while still achieving stable fixation.