Rounded-rectangular bone tunnels enhance early tendon-bone healing and limit tunnel enlargement in a rabbit anterior cruciate ligament reconstruction with quadriceps tendon graft model.

Abstract

PURPOSE: To determine whether rounded-rectangular bone tunnels matching the flat morphology of a quadriceps tendon (QT) graft enhance early tendon-bone healing (TBH) and suppress bone-tunnel enlargement (BTE) after anterior cruciate ligament (ACL) reconstruction in a rabbit model. METHODS: Female Japanese White rabbits underwent ACL reconstruction with a QT graft and were randomized into circular or rounded-rectangular tunnels. Knees were evaluated at 4, 8, and 12&#xa0;weeks (n&#xa0;=&#xa0;10/group/time point; total, 60). Micro-computed tomography quantified tunnel cross-sectional area and flattening ratio, with BTE (%) calculated vs. baseline. Histological TBH at the tendon-bone interface was semi-quantitatively scored (n&#xa0;=&#xa0;4/group/time point), and biomechanical testing assessed maximum failure load and mode of failure (n&#xa0;=&#xa0;6/group/time point). Non-parametric tests were used to compare groups, and repeated-measures analysis of variance was used to assess temporal changes. RESULTS: The rounded-rectangular tunnel group (Group R) showed significantly lower BTE than the circular tunnel group (Group C) at 4 and 8&#xa0;weeks (both p&#xa0;<&#xa0;0.05). Flattening ratios did not differ between groups at 4-12&#xa0;weeks. In both groups, tunnel area increased from time 0 to a peak at 4&#xa0;weeks and then slightly decreased and stabilized by 8-12&#xa0;weeks. The histological scores favored Group R at 4&#xa0;weeks (P&#xa0;=&#xa0;0.038). The maximum failure load was higher in Group R at 4&#xa0;weeks (P&#xa0;=&#xa0;0.03). CONCLUSION: Matching QT grafts with rounded-rectangular tunnels suppresses early BTE and enhances early histological integration and fixation strength after ACL reconstruction, potentially enabling safer and earlier rehabilitation.