Abstract： Background There are different materials used for anterior cruciate ligament(ACL)reconstruction.It has been reported that both autologous grafts and allografts used in ACL reconstruction can cause bone tunnel enlargement.This study aimed to observe the characteristics of bone tunnel changes and possible causative factors following ACL reconstruction using Ligament Advanced Reinforcement System(LARS)artificial ligament.Methods Forty-three patients underwent ACL reconstruction using LARS artificial ligament and were followed up for 3 years.X-ray and CT examinations were performed at 1,3,6,12,24,and 36 months after surgery,to measure the width of tibial and femoral tunnels.Knee function was evaluated according to the Lysholm scoring system.The anterior and posterior stability of the knee was measured using the KT-1000 arthrometer.Results According to the Peyrache grading method,grade 1 femoral bone tunnel enlargement was observed in three cases six months after surgery.No grade 2 or grade 3 bone tunnel enlargement was found.The bone tunnel enlargement in the three cases was close to the articular surface with an average tunnel enlargement of(2.5±0.3)mm.Forty cases were evaluated as grade 0.The average tibial and femoral tunnel enlargements at the last follow-up were(0.8±0.3)and(1.1±0.3)mm,respectively.There was no statistically significant difference in bone tunnel width changes at different time points(P＞0.05).X-ray and CT measurements were consistent.Conclusions There was no marked bone tunnel enlargement immediately following ACL reconstruction using LARS artificial ligament.Such enlargement may,however,result from varying grafting factors involving the LARS artificial ligament or from different fixation methods.