To evaluate the effect of hybrid grafts (augmenting autografts with allograft tissue) with different diameters on the knee kinematic characteristics after anterior cruciate ligament reconstruction (ACLR).

The data of 57 patients were retrospectively analyzed who had undergone ACL reconstruction using hybrid graft in the Third Affiliated Hospital of Southern Medical University from August 2017 to June 2018. Inclusion criteria: patients with unilateral knee ACL injury and ACL reconstruction with eight-or nine-minimeter-diameter hybrid graft; the age were 18 to 55 years and radiographic evidence showed epiphyseal closure. Exclusion criteria: X-ray suggested osteoarthritis of the knee; the preoperative knee movement was limited; other knee surgery history; injury of other ligaments of knee joint; the patients requiring meniscus transplantation and cartilage repair simultaneously. According to the diameter of grafts, they were divided into the eight-millimeter group (32 cases) and nine-millimeter group (25 cases). The patients were followed up preoperatively and in postoperative six months, one and two years. The rang of motion (ROM) in six degrees of freedom (6DOF) and tibiofemoral kinematics of the involved knee (the contralateral knee joint was used as control), the graft signal/noise quotient (SNQ) value, and Lysholm score were analyzed. Preoperative and postoperative data of each group were compared by repeated measure ANOVA.

There was no statistically significant difference in the failure rate between the eight-millimeter group (6.3%) and the nine-millimeter group (0%) (P=0.499). In the eight-millimeter group, flexion in the postoperative six months and external rotation in the postoperative one years were higher than those in the nine-millimeter group, and the differences were statistically significant (F=3.507, P=0.034; F=4.563, P=0.013). In the eight-millimeter group, lateral displacement in the postoperative six months and external rotation in the postoperative two years were higher than those in the control group, and the differences were statistically significant (F=3.596, P=0.031; F=9.997, P<0.001). Compared with the data of postoperative six months and one year, graft SNQ values in both groups showed a decreasing trend in the postoperative two years (F=9.634, 8.593, 7.636, all P < 0.001). Lysholm score in the nine-millimeter group was higher than that in the eight-millimeter group, and the difference was statistically significant (F=6.116, P=0.017).

Hybrid grafts with diameters of eight millimeters and nine millimeters have a comparable rerupture rate and similar graft maturity after ACLR, but the knee kinematics of the latter are more similar to that of the normal knee than the former.