 The investigators divide 100 patients with ACL rupture into 2 groups. Group A undergo single bundle anterior cruciate ligament reconstruction ACLR. Group B undergo double bundle ACL reconstruction. At 3-6 weeks post operation, all the patients undergo 3-D MRI examination of both knees. The investigators reconstruct 3-D models of reconstructed ACL and native ACL, and compare the difference between single and double bundle graft. 