Superior Biological Healing of Hamstring Autografts Compared with Tibialis Allografts after Anterior Cruciate Ligament Reconstruction: A Propensity Score Matching Analysis Based on Second-Look Arthroscopy

<i>Background and Objectives:</i> Remodeling and healing of the graft are crucial processes for long-term graft survival after anterior cruciate ligament reconstruction (ACLR). However, few studies have objectively evaluated the differences in graft healing between autografts and allografts. This study aimed to compare the status of the anterior cruciate ligament (ACL) grafts between hamstring tendon (HT) autografts and tibialis anterior tendon (TAT) allografts using second-look arthroscopy. <i>Materials and Methods:</i> The outcomes of 193 consecutive patients (153 males and 40 females, with an average age of 30.38 and BMI of 25.43 kg/m²) who underwent second-look arthroscopy following primary ACLR were retrospectively reviewed. Prior to participating in this study, all patients provided written informed consent. The patients were divided into two groups: those with HT autografts and those with TAT allografts. Confounding factors were matched between the two groups using propensity score matching (PSM). ACL graft status was assessed during second-look arthroscopy using a numeric scale system based on the degree of four parameters: graft tension, continuity, synovium coverage, and vascular marking. Clinical outcomes were assessed using the Lysholm and International Knee Documentation Committee (IKDC) scores. Graft status and clinical outcomes were compared between the two groups. Additionally, a subgroup analysis based on the timing of the second-look arthroscopy (12-24 months vs. >24 months after the initial ACLR) was conducted. <i>Results:</i> After PSM, 62 patients were included in each group. The second-look arthroscopy was conducted at 23.6 ± 6.6 months for the HT group and at 24.0 ± 7.9 months for the TAT group (<i>p</i> = 0.749). The continuity and tension of the ACL graft were not significantly different between the two groups (<i>p</i> = 0.146 and 0.075, respectively). However, the TAT group exhibited significantly inferior synovial coverage and vascular marking of the ACL graft compared with the HT group (<i>p</i> = 0.021 and 0.007, respectively). These findings were consistent regardless of the timing of the second-look arthroscopy. Clinical outcomes, according to the Lysholm and IKDC scores, significantly improved in both groups with no significant differences (<i>p</i> = 0.386 and 0.733, respectively). <i>Conclusions:</i> Although there were no differences in graft tension and continuity between HT autografts and TAT allografts, the biological healing of ACL grafts, in terms of synovialization and vascularization, was superior in HT autografts compared to TAT allografts.