Objective: Anterior cruciate ligament reconstruction (ACLR) with autologous hamstring tendon is the standard treatment for ACL rupture. However, tibial tunnel enlargement and delayed graft maturation may affect long-term outcomes. Evidence on their mid- to long-term associations with clinical recovery remains limited. The main objectives of this study include: (i) analyze longitudinal changes in tibial tunnel morphology after single-bundle ACLR; (ii) quantitatively evaluate graft maturation at different tunnel regions using the signal intensity ratio (SIR) from MRI; and (iii) examine the correlations between tibial tunnel enlargement, graft healing, and clinical outcomes.
Methods: A retrospective study was conducted on 35 patients who underwent single-bundle ACLR using autologous hamstring grafts and completed a 5-year follow-up. Knee function was evaluated preoperatively and at 2 and 5 years postoperatively using the KT-2000 arthrometer, pivot-shift test (PST) grade, Lysholm Knee Scoring Scale, International Knee Documentation Committee (IKDC) questionnaire, Knee injury and Osteoarthritis Outcome Score (KOOS), Tegner Activity Scale, and the Anterior Cruciate Ligament-Return to Sport after Injury (ACL-RSI) scale. Tibial tunnel diameter was measured via MRI at 1 week, 2 years, and 5 years postoperatively. Graft maturation was evaluated using the signal intensity ratio (SIR). Changes in tunnel diameter and SIR over time were analyzed. Pearson correlation coefficients (r) were used to assess the relationship between bone tunnel enlargement (BTE), graft healing, and knee function. Spearman's rank correlation coefficient was used to assess the association between BTE and PST grade.
Results: Tibial tunnel diameter increased from 1 week to 2 years and partially regressed at 5 years, remaining larger than baseline. SIR increased significantly from 1 week to 2 years and decreased slightly by 5 years. At 2 years, tunnel diameter in the tibial tunnel exit (ttE) region was positively correlated with intra-articular graft SIR (r = 0.455, p < 0.01), but not with clinical outcomes. By 5 years, no significant correlation was observed between tibial tunnel diameter and graft SIR. However, tibial tunnel diameter in the ttE region was positively correlated with KT-2000 side-to-side difference (SSD) (r = 0.411, p < 0.05).
Conclusion: Tibial tunnel enlargement progressed until 2 years post-ACLR, then partially regressed by 5 years. BTE was associated with graft healing at 2 years and with anterior knee stability at 5 years but had no significant adverse impact on long-term clinical outcomes.
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