Injury thresholds of knee ligaments under lateral-medial shear loading: an experimental study.

OBJECTIVE Knee ligament injuries frequently cause devastating impairment to the injured. In car-pedestrian impact accidents, lateral-medial shear displacement is one of principal mechanisms of knee ligament injuries. The current study aims to investigate injury thresholds of knee ligaments under lateral-medial shear loading to improve pedestrian safety. METHODS Ten isolated human knee joints without surrounding muscles were tested under dynamic lateral-medial shear loading in 2 groups: 3 left knee joints were tested in the shearing of medial tibial translation, and other knee joints were tested in lateral tibial translation. Based on combined analysis of experimental videos and force curves, the primary failure time of knee ligaments and the corresponding shear displacement were determined. RESULTS Under lateral tibial translation and medial tibial translation, both primary injury types of knee ligaments and force curves showed essential differences. It appears that the majority of primary failure modes were anterior cruciate ligament (ACL) injury when the tibia was displaced medially and posterior cruciate ligament (PCL) injury when the tibia was displaced laterally. Overall experimental results indicated that the injury threshold of the knee joint under lateral-medial shear loading varied from 11.4 to 17.6 mm, with an average level approximately 14.3 mm. CONCLUSION Based on the bone-ligament-bone complex experiment of the knee, we present injury occurrences of the knee joints in lateral and medial shear loading. The testing data provide a basis for improving knee injury criteria that regulate passenger cars to reduce their aggressiveness to pedestrians.