Effect of Tunnel-Graft Length on the Biomechanics of Anterior Cruciate Ligament-Reconstructed Knees Intra-articular Study in a Goat Model

Background: In anterior cruciate ligament (ACL) reconstruction using hamstring grafts, the graft can be looped, resulting in an increased graft diameter but reducing graft length within the tunnels. Hypothesis: After 6 and 12 weeks, structural properties and knee kinematics after soft tissue ACL reconstruction with 15 mm within the femoral tunnel will be significantly inferior when compared with the properties of ACL reconstruction with 25 mm in the tunnel. Study Design: Controlled laboratory study. Methods: In an intra-articular goat model, 36 ACL reconstructions using an Achilles tendon split graft were performed with 15-mm (18 knees) and 25-mm (18 knees) graft length in the femoral tunnel. Animals were sacrificed 6 weeks and 12 weeks after surgery and knee kinematics was tested. In situ forces as well as the structural properties were determined and compared with those in an intact control group. Histologic analyses were performed in 2 animals in each group 6 and 12 weeks postoperatively. Statistical analysis was performed using a 2-factor analysis of variance test. Results: Anterior cruciate ligament reconstructions with 15 mm resulted in significantly less anterior tibial translation after 6 weeks (P < .05) but not after 12 weeks. Kinematics after 12 weeks and in situ forces of the replacement grafts at both time points showed no statistically significant differences. Stiffness, ultimate failure load, and ultimate stress revealed no statistically significant differences between the 15-mm group and the 25-mm group. Conclusion: The results suggest that there is no negative correlation between short graft length (15 mm) in the femoral tunnel and the resulting knee kinematics and structural properties. Clinical Relevance: Various clinical scenarios exist in which the length of available graft that could be pulled into the bone tunnel (femoral or tibial) could be in question. To address this concern, this study showed that reducing the tendon graft length in the femoral bone tunnel from 25 mm to 15 mm did not have adverse affects in a goat model.