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

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. 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 weeks (n = 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 = 4/group/time point), and biomechanical testing assessed maximum failure load and mode of failure (n = 6/group/time point). Non-parametric tests were used to compare groups, and repeated-measures analysis of variance was used to assess temporal changes. The rounded-rectangular tunnel group (Group R) showed significantly lower BTE than the circular tunnel group (Group C) at 4 and 8 weeks (both p < 0.05). Flattening ratios did not differ between groups at 4-12 weeks. In both groups, tunnel area increased from time 0 to a peak at 4 weeks and then slightly decreased and stabilized by 8-12 weeks. The histological scores favored Group R at 4 weeks (P = 0.038). The maximum failure load was higher in Group R at 4 weeks (P = 0.03). 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.