Static Stability (Laxity) The KT-2000 knee ligament arthrometer (MED Metric Co., San Diego, USA) is designed to assess the anterior drawer laxity of the knee joint. The discrepancy of anterior displacement between the sound side and the lesion side had been reported and applied in evaluating the static stability of the knee, and it was also used as one of the references for the ACL reconstruction surgery. In this current study, a discrepancy less than 1.5mm was normally accepted when 20-pound anterior traction force was exerted on the tibia with the knee joint in 20° flexion. In contrast, ACL laxity was defined as a discrepancy over 3mm, which was highly related to ACL injury.