Is Bone Mineral Density at the Tendon-Bone Interface After ACL Reconstruction Associated With Graft Maturation? A Quantitative Computed Tomography Analysis

Background: The revision rate due to postoperative instability after anterior cruciate ligament reconstruction (ACLR) remains at 4% to 25%. The physiological mechanisms of tendon-bone healing involve intricate processes, particularly neovascularization and osseointegration at the bone tunnel interface. Currently, no standardized noninvasive method exists to comprehensively evaluate tendon-bone healing progression. Purpose: To investigate longitudinal changes in bone mineral density (BMD) at tendon-bone interface (TBI) sites after ACLR and evaluate their associations with graft maturation and clinical outcomes. Study Design: Cohort study; Level of evidence, 2. Methods: This prospective study enrolled 36 consecutive patients undergoing arthroscopic all-inside single-bundle ACLR using a hamstring autograft between October 2020 and October 2021. Quantitative CT assessments using phantom-less software measured BMD at femoral (anterior, posterior, proximal, and distal) and tibial (anterior, posterior, medial, and lateral) tunnel regions (entry/mid/exit segments) at postoperative day 1 (baseline), 6 months, 1 year, and 2 years. Graft maturity was evaluated via the signal-to-noise quotient (SNQ) on magnetic resonance imaging at 1- and 2-year follow-ups. Results: Significant increases in volumetric BMD (vBMD) were observed at different segments and orientations in the femoral and tibial tunnel regions. From baseline to 6 months, femoral tunnel segments showed increases ranging from +36.1% to +52.7%, and tibial segments from +44.9% to +57.5% ( P < .05). From 6 months to 1 year, additional gains were observed in most regions (femoral: +22.4% to +26.1%; tibial: +15.8% to +19.2%; P < .05). However, changes between 1 and 2 years were generally smaller (femoral: +8.6% to +12.5%; tibial: +6.9% to +19.2%) and not statistically significant in all segments and orientations ( P > .05). Graft SNQ values demonstrated regional variations, with femoral tunnel areas showing higher values than tibial regions at both the 1-year and 2-year assessments. No significant changes occurred between 1- and 2-year. Negative correlations emerged between BMD changes and SNQ values in corresponding regions (femoral: r = −0.477 to −0.542; tibial: r = −0.427 to −0.493; P < .05). Conclusion: Within 2 years after ACLR, the BMD at the TBI of both femoral and tibial bone tunnels demonstrates a progressive increase. The BMD at these TBIs shows positive correlations with graft maturity at corresponding anatomic locations, providing a valuable reference for clinical assessment of tendon-bone healing.