The effect of the point of application of anterior tibial loads on human knee kinematics

Coupled axial tibial rotation in response to an anterior tibial load has be en used as a common diagnostic measurement and as a means to load the ligam entous structures during laboratory tests. However, the exact location of t he point of application of these loads as well as the corresponding sensiti vity of the coupled tibial rotation to this point can have an effect on the function of the soft tissues at the joint. Therefore, the purpose of this study was to determine the effects of four different points of application of the anterior tibial load on the anterior tibial translation and coupled axial tibial rotation. The four points include: (1) geometric point - midwa y between the collateral ligament insertion sites on the tibia, (2) clinica l point - a position that attempts to simulate clinical diagnostic tests, ( 3) medial point - a position medial to the geometric point and (4) lateral point - a position lateral to the clinical point. A robotic/universal force -moment sensor testing system was used to apply the anterior tibial load at the four points of application and to record the resulting joint motion. A nterior tibial translation in response to an anterior tibial load of 100 N was found not to vary between the four points of application of the anterio r tibial load at all flexion angles examined. However, internal tibial rota tion was found for the lateral point (13 +/- 10 degrees at 30 degrees of kn ee flexion) in all specimens and clinical point (8 +/- 10 degrees at 30 deg rees of knee flexion) while external rotation resulted when the load was ap plied at the medial point (-8 +/- 7 degrees at 30 degrees of knee flexion). Both internal and external tibial rotations occurred throughout the range of flexion when the tibial load was applied at the geometric point. The res ults suggest that the clinical point should be used as the point of applica tion of the anterior tibial load whenever clinical examinations are simulat ed and multi-degree-of-freedom joint and soft tissue function are examined. (C) 2000 Elsevier Science Ltd. All rights reserved.