2017 ISAKOS Biennial Congress ePoster #1126
Graft Shift in Femoral Tunnel with Single-Bundle Anterior Cruciate Ligament Reconstruction
Junjun Zhu, BS, MS, Pittsburgh, PA UNITED STATES
Brandon D. Marshall, MS, Pittsburgh, PA UNITED STATES
Libin Zheng, MD, Xiamen, Fujian CHINA
Shuzhen Li, MD, Pittsburgh, PA UNITED STATES
Monica A. Linde, MS, RN, Pittsburgh, PA UNITED STATES
Patrick J. Smolinski, PhD, Pittsburgh, PA UNITED STATES
Freddie H. Fu, MD, Pittsburgh, PA UNITED STATES
Department of Orthopaedic Surgery, University of Pittsburgh, Pittsburgh, Pennsylvania, UNITED STATES
FDA Status Not Applicable
According to the results of this study, the biggest shift of the graft in the femoral tunnel occurred during knee flexion extension, the shifts during anterior/posterior loading were greater than the shifts during internal/external rotation and valgus loading.
Femoral tunnel widening is a common complication of anterior cruciate ligament (ACL) reconstruction. Mechanical explanations for the widening include the windshield wiper effect and bungee effect as the graft moves inside the tunnel during knee motion . Nonetheless, a correlation between widening and knee motion has not been demonstrated and graft motion has not been well quantified.
Five (n=5) fresh frozen unpaired adult porcine knees were used for testing. Single bundle anatomical ACL reconstruction was performed with an 8mm femoral tunnel and a 7 mm graft which was fixed with 60 N at 30° of flexion. Specimens were tested with the robotic testing system under (1) an 89-N anterior tibial (AT) and posterior tibial (PT) load at 30° (porcine full extension), 60°, and 90° of knee flexion, (2) 4-Nm internal and external tibial torques at 30° and 60°, and (3) a 7-Nm valgus torque at 30° and 60° of knee flexion [2,3]. The geometry and the position of the tunnel and graft were measured using a digitizer (FARO Technologies Inc). The amount of the graft shift was defined as the distance the centroid of the graft cross section moved during loading. The tunnel appears as an oval because of its projection to the sagittal plane. The shifts in anterior/posterior, superior/inferior were all defined with respect to a femoral coordinate system.
During flexion/extension, the shifted distance from 30° to 60° is greater (10.08% of tunnel diameter) than the one from 60° to 90° (2.41% of tunnel diameter). The ACL graft would shift in the direction of loading under AT and PT loadings, averagely 6.69% and 6.89 % of the tunnel diameter. Under IR and ER, the average shift is 2.34% and 1.72% respectively. Under valgus loading, the average shift is 4.47%.
The graft shifted within the tunnel during knee flexion/extension. The ACL graft would shift in the direction of loading under AT and PT loadings. Under IR and ER, the shift is greater at higher flexion angles. Under valgus loading, the shift is greater at low flexion angles. Clinically, the graft shift in the femoral tunnel may result in tunnel enlargement and can be affected by tunnel position as well in ACL reconstruction.
References: 1. Cheung et al. Journal of Orthopaedic surgery (Hong Kong), 2010. 2.Yuki Kato et al., Knee Surgery, Sports Traumatology, Arthroscopy, 2012. 3.Brian T. Feeley, et al. The American Journal of Sports Medicine, 2009