Bilateral anterior cruciate ligament reconstruction is more vulnerable to graft failure than unilateral anterior cruciate ligament reconstruction

Abstract Purpose To investigate the graft survival rates of bilateral anterior cruciate ligament reconstruction (ACLR) and to evaluate whether the graft failure rate of bilateral ACLR is different from that of unilateral ACLR. Hypothesis The graft survival rate of bilateral ACLR is lower than that of unilateral ACLR. Methods All ACLRs followed up in our institution from 1997 to 2022 were retrospectively identified. ACLRs were divided into the bilateral and unilateral ACLR groups. Each ACLR was classified as bilateral group if contralateral knee had undergone ACLR; otherwise, it was classified as unilateral ACLR group. Simultaneous ACLRs were excluded. Given the demographic heterogeneity between the groups, propensity score matching was performed with the following covariates: age, sex, body mass index, graft, meniscus lesion and follow‐up period. Before and after propensity score matching, the survival rates of the two groups were compared using Kaplan–Meier survival analysis. Survival analysis was performed separately for each ACLR. In addition, clinical outcomes determined by the Lysholm score and the International Knee Documentation Committee (IKDC) score of the last outpatient visit were compared between groups. Graft failure was defined as cases that underwent revision ACLR or were recommended for revision ACLR due to objective instability on physical examination and confirmed graft rupture on MRI. Results In total, 979 cases of ACLRs met the inclusion and exclusion criteria, of which 94 were bilateral and 885 were unilateral ACLRs. Kaplan–Meier survival analysis showed a significantly lower survival rate in the bilateral ACLR group than that of the unilateral ACLR (log‐rank test, p = 0.035). After matching for baseline characteristics, which left 94 ACLRs per group, the survival rate was significantly lower in the bilateral group (log‐rank test, p = 0.033). Regarding clinical outcomes, the mean Lysholm and IKDC scores were significantly lower in the bilateral ACLR group compared with the unilateral ACLR group both before (85.3 ± 16.1 vs. 93.8 ± 8.1, p < 0.001; Lysholm, 73.0 ± 17.0 vs. 84.1 ± 11.4, p < 0.001; IKDC) and after matching (85.7 ± 15.9 vs. 91.6 ± 9.4, p = 0.014; Lysholm, 73.4 ± 16.7 vs. 73.4 ± 16.7, p = 0.008; IKDC). Conclusion Bilateral ACLR is more vulnerable to graft failure than unilateral ACLR. In addition, bilateral ACLR is associated with worse clinical outcomes. Thus, bilateral ACL injury should not be regarded as merely the result of two independent unilateral ACL injuries. Rather, the two conditions should be considered distinct clinical entities. When treating bilateral ACL injury, greater efforts should be made to manage factors known to affect graft survival and more cautious rehabilitation protocol should be adopted. Level of Evidence Level III, case–control study.