Revision Risk Of Soft Tissue Allograft Versus Hybrid Graft Following Anterior Cruciate Ligament Reconstruction
Authors: Mirzayan Raffy , Prentice Heather A. , Essilfie Anthony , Burfeind William , Ding David Y. , Maletis Gregory B. 
Published: March 2020

Objectives: Prior studies have found smaller hamstring autograft diameter to be associated with a higher revision risk following anterior cruciate ligament reconstruction (ACLR). Therefore, when a harvested hamstring autograft is deemed by the surgeon to be of inadequate diameter, the options include: using the small graft, using another autograft from a different site, augmenting with an allograft (hybrid graft), or abandoning the autograft and using allograft alone. Using another autograft site includes added harvest-site morbidity, therefore utilization of an allograft to augment the autograft (hybrid) or allograft alone may be an appealing alternative option. Revision risk for hybrid graft compared to soft tissue allograft in is not known. The purpose of our study was to determine the risk for aseptic revision following soft tissue allograft ACLR compared to hybrid graft ACLR in patients 25 years and younger. Methods: Data from a healthcare system’s ACLR registry was used to conduct a cohort study. Primary isolated unilateral ACLR from 2009-2016 using either a hybrid graft (hamstring autograft + soft tissue allograft) or soft tissue allograft alone were identified. Time-to-aseptic revision surgery following primary ACLR was the primary endpoint. Multivariable Cox proportional hazard regression was used to evaluate risk for aseptic revision according to graft utilization after adjustment for age, allograft processing, tunnel drilling technique, and region where the primary ACLR was performed. Analysis censored patients at the time lost to follow-up (healthcare plan termination or death) or the end of study follow-up. A sandwich covariance matrix estimator was used to account for clustering of ACLR at the surgeon level. Results: The cohort included 2080 ACLR performed by 161 surgeons at 42 healthcare centers. Soft tissue allograft was used for 1601 (77.0%) ACLR and hybrid graft for 478 (23.0%). For the soft tissue allograft ACLR group, mean age was 19.2 (standard deviation [SD]=3.5) years, 79.1% of allografts were irradiated or chemically processed, and 50.4% of femoral tunnels were through the trans-tibial technique. For the hybrid graft ACLR group, mean age was 18.4 (SD=3.3) years, 81.5% were irradiated or chemically processed, and 72.3% of femoral tunnels were through the trans-tibial technique. Median follow-up time was 3.4 years (interquartile range=1.8-5.1 years). The crude 2-year aseptic revision probability was 5.4% (95% confidence interval [CI]=4.3-6.7) for soft tissue allograft ACLR and 3.8% (95% CI=2.3-6.4) for hybrid ACLR. After adjustment for covariates, soft tissue allograft ACLR had a higher risk of aseptic revision during follow-up compared to hybrid graft ACLR (hazard ratio=2.00, 95% CI=1.21-3.31, p=0.007). Conclusion: Soft tissue allograft had twice the risk of aseptic revision compared to hybrid graft following ACLR. Based on our findings, when faced with a hamstring autograft that is deemed to have an inadequate diameter, augmenting it with allograft tendon may be preferred over abandoning it for an allograft alone. Future study evaluating the indications and the optimal hybrid graft diameter is needed.