Allograft and autograft anterior cruciate ligament reconstructions exhibit a similar biological response to cyclic loading

Objective: Anterior cruciate ligament (ACL) reconstruction is one of the most commonly performed orthopaedic procedures. While outcomes are similar in the general patient population, the rerupture rate of non-irradiated allografts are 3–4 times higher than autografts in young active individuals. Previous studies suggest that the difference in clinical performance between graft types is due to impaired remodeling in allografts in response to loading. The objective of this study was to compare the remodeling response of autografts and allografts to cyclic loading. Furthermore, given that allografts are a foreign object and that immune cell signaling affects fibroblast mechanobiology, we compared markers of the immune cell composition between graft types. Methods: ACL reconstructions were performed on New Zealand white rabbits, harvested 8 weeks post-surgery, and cyclically loaded to 2 MPa in a tensile bioreactor. Expression of markers for anabolic and catabolic tissue remodeling, as well as inflammatory cytokines and immune cells, were quantified using quantitative reverse transcription polymerase chain reaction. Results: We found that the expression of markers for tissue remodeling were not different between allografts and autografts. Similarly, we found that the expression of markers for immune cells were not different between allografts and autografts. Conclusions: These data suggest that the poor clinical outcomes and impaired remodeling of allograft reconstructions compared to autografts is not due to a difference in graft mechanobiology.