Comparison of Long-Term Tunnel Widening in Anterior Cruciate Ligament Reconstruction Using Allograft and Hamstring...

Bone tunnel widening following anterior cruciate ligament reconstruction (ACLR) is a well-recognized radiological phenomenon with multifactorial etiology. While concerns have been raised regarding potentially greater tunnel enlargement with allografts due to immune-mediated responses, evidence remains inconsistent. This study compared long-term femoral and tibial tunnel widening between hamstring autograft and allograft reconstruction at a mean follow-up exceeding 10 years. A retrospective analysis was conducted on 60 patients who underwent primary ACLR between 2011 and 2016 by a single surgeon. Group I consisted of 29 patients receiving soft tissue allografts (Achilles, tibialis anterior, or peroneus longus tendons), while Group II included 31 patients with four-strand hamstring autografts. All procedures utilized identical fixation: adjustable-loop suspension device (femur) and bioabsorbable interference screw with tibial staple. Patients with previous knee surgery, re-rupture, clinical graft failure, concomitant ligament procedures, or significant chondral lesions were excluded. Computed tomography scans at final follow-up (mean: 10.7 years) were analyzed using standardized oblique reformatted sections perpendicular to tunnel axes. Six measurements per tunnel (three levels × two planes) were averaged. Tunnel widening was expressed as absolute change (Δmm) and percentage relative to intraoperative drill bit diameter. Two blinded orthopedic surgeons performed independent measurements. Statistical analysis included Mann-Whitney U test, analysis of covariance adjusted for body mass index (BMI) and follow-up duration, categorical threshold analysis, and correlation analysis with Bonferroni correction. No significant differences were observed between groups for tibial widening (allograft 2.07 ± 1.75 mm vs. autograft 2.31 ± 1.72 mm, p = 0.500) or femoral widening (1.73 ± 1.48 mm vs. 2.30 ± 1.63 mm, p = 0.157). After adjustment for BMI and follow-up duration, between-group differences remained nonsignificant (all adjusted p > 0.0125 after Bonferroni correction). Categorical distribution across predefined thresholds showed similar patterns. Initial tunnel diameter inversely correlated with tibial percentage widening (r =-0.373, p = 0.003). Interobserver reliability was excellent (intraclass correlation coefficient: 0.89-0.92). At long-term follow-up, allograft and hamstring autograft demonstrated comparable tunnel widening patterns, suggesting graft selection should prioritize clinical factors beyond tunnel enlargement concerns.