抄録
MRI studies for shapes and sizes of anterior cruciate ligament (ACL) and of knee-joint condyles were performed respectively, on twelve female high-school students; all play basketball in the same team as an extracurricular activity. Six sustain noncontact ACL injury, the other six have no problems with their knees. Among various measures, only the index of convexity of the lateral tibial plateau revealed statistically significant difference between the ACL injury and the normal. It was suggested that the shape of convexity of the lateral tibial plateau is associated with ACL elongation during knee motion, thereby causing noncontact injuries.
A 3 D knee model was developed in order to complement the experimental results by determining a direct relationship between convexity of the lateral tibial plateau and ACL elongation as a function of knee angle. The articular surfaces were approximated by the spline equations. The ligaments and fascia were represented by a number of non-linear springs. A sensitivity study was undertaken to evaluate ACL elongation due to the variations in convexity of the lateral tibial plateau and in magnitude of floor reaction force/moment. A hyperboloid was mathematically heaped up to the original lateral tibial plateau so as to increase the convexity as well as to heighten the intercondylar tubercle.
Simulation results demonstrated that when the intercondylar tubercle became higher by 1mm, ACL strain increased by about 20 to 30%; same amount when a value of internal rotation moment to the tibia increased by 10Nm. An increase in convexity of the lateral tibial plateau increased ACL strain especially for small angle of knee flexion, which is the condition at the moment of jumping or landing.
We conclude that athletes with larger convexity of the lateral tibial plateau are at significantly greater risk for sustaining noncontact ACL injury.
