Tensions generated in selected bands of the four major ligaments of the flexed knee (40-90 degrees) have been measured in vitro when the tibia is subjected to passive anterior translation and axial rotation with and without a compressive preload. The measurements were made in 30 fresh-frozen specimens using the buckle transducer attached to the anteromedial band of the anterior cruciate ligament [ACL (am)], the posterior fibres of the posterior cruciate ligament [PCL (pf)], the superficial fibres of the medial collateral ligament [MCL (sf)], and in the total lateral collateral ligament (LCL). Particular attention was placed on the evaluation of the performance of the transducer specific to such measurements in order to minimize the errors associated with the use of this transducer. The results indicate that, among the measured ligaments, substantial tension (greater than 20 N) is generated only in the ACL (am) in tibial anterior translation up to 5 mm. The tension pattern generated in response to tibial axial rotation, however, is complex and exhibits considerable variation between specimens. In general, both the MCL (sf) and LCL are tensed at all tested flexion angles, with the tension in external rotation being significantly greater than in internal rotation. At 40 degrees of flexion, the ACL (am) bears tension mainly in internal rotation, while at 90 degrees of flexion the PCL (pf) is tensed in both senses of rotation. The response of the LCL shows marked variation among specimens; very small tension (less than 15 N) is generated in internal rotation in 48% of the specimens, and in either sense of rotation in 20% of the specimens. The tension in the ACL (am) in internal rotation is invariably greater in those specimens in which LCL tension is negligible. This correlation between increased ACL (am) function and inadequate LCL restraint appears significant in terms of ACL injury and repair.

The aim of this study is an experimental evaluation of a force analysis of the patellar mechanism based on the assumption that patellofemoral contact is frictionless. At first, the geometric characteristics of contact surfaces, a prior knowledge of which is necessary for quantitative analysis, were measured from radiographs of 42 fresh-frozen knee specimens in the flexion range 0-120 degrees. The results were then used in the analysis to predict the relations between the forces acting on the patella. For the evaluation of the analysis, the ratio of the tension in the ligamentum patellae and the rectus femoris was measured in ten specimens during simulation of two knee functions: (1) "leg raising" against a resistance; and (2) "static lifting". The effect of flexion angle on the ratio is found to be rather complex. With increasing flexion, the ratio increases initially up to 30 degrees, then decreases up to 90 degrees, and finally increases again beyond 90 degrees. The ratio is above unity up to around 45 degrees and below that in the remaining flexion range. The analysis has been found to predict not only the characteristic variation of the ratio but also its magnitude with reasonable accuracy. It has been concluded that for an accurate prediction of the patellofemoral joint reaction, the force analysis needs to be based on the geometry of the contact surfaces. This implies that the mechanical consequences of surgical procedures involving tibial tubercle relocation cannot be inferred simply on the basis of their effect on the patellar mechanism angle, but that they also require consideration of their effect on the contact geometry.

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