Effect of graft tensioning on mechanical restoration in a rat model of anterior cruciate ligament reconstruction using free tendon graft

Abstract

Initial graft tensioning is important in anterior cruciate ligament reconstruction (ACLR), but its effect on graft healing is still not clear. Since all previous animal studies on graft tensioning used bone-patellar tendon-bone, this study aimed to investigate the effect of initial graft tensioning on ACLR using tendon graft. Fifty-five Sprague-Dawley rats underwent ACLR using flexor digitorum longus tendon graft. A constant force of 2 or 4N was applied during graft fixation. At 0, 2, and 6weeks, knee samples were harvested (n=6) for static knee laxity test and graft pull-out test. Histological examination was performed at 2 and 6weeks post-injury (n=4). At time zero, knee laxity was restored by ACLR with 2 or 4N tensioning as compared to ACL-deficient group (p<0.001), and the 4N group exhibited a better restoration as compared to 2N group (p=0.031). At week 2 post-operation, the 4N group still exhibited a better restoration in knee laxity (p=0.001) and knee stiffness (p=0.002) than the 2N group; the graft pull-out force (p=0.032) and stiffness (p=0.010) were also higher. At week 6 post-operation, there was no significant difference between the 2 and 4N group in knee laxity and graft pull-out strength. Histological examination showed that the beneficial effect of higher initial graft tension may be contributed by maintenance of graft integrity at mid-substance and reduction in adverse peri-graft bone changes in the femoral tunnel region. A higher initial graft tension favours the restoration of knee laxity and promotes graft healing in ACLR using free tendon graft in the rat model.