The work of this dissertation was motivated by the need to further our understanding of the contribution of individual fiber bundles of ligaments in restraining the motion of the knee joint and to further our understanding of the effects of anterior cruciate ligament (ACL) deficiency and of ACL reconstructions on the mechanics of the knee for physiological levels of quadriceps loads. Thus, the objectives of this work were to determine (1) the effects of the physiological levels of quadriceps loads on the length changes of the four major ligaments of the knee, (2) the effects of ACL deficiency and of ACL reconstructions on the kinematics of the tibiofemoral and patellofemoral joints, and (3) the effects of ACL deficiency and of ACL reconstructions on patellofemoral contact characteristics. Three studies were performed with a six-degree-of-freedom digitizing system.

In the first study, the motion of the tibiofemoral joint and the lengths of selected fiber bundles of the major ligaments of the knee were measured during passive flexion and during quadriceps loading in fifteen cadaveric knees. Six bundles were identified for the ACL, six for the posterior cruciate ligament (PCL), three for the medial collateral ligament (MCL), and one for the lateral collateral ligament (LCL). Quadriceps loads were applied to equilibrate each of four magnitudes of flexion moments equivalent to 1/12, 1/6, 1/4, and 1/3 of values reported in the literature for maximum isometric extension moments. Linear regression analysis was performed to model the length of each fiber bundle as a function of the magnitude of the externally applied flexion moment for flexion angles ranging from 0° to 120° in 15° increments. Both internal tibial rotations and anterior tibial translations during quadriceps loading were significantly greater than those during passive knee flexion. During quadriceps loading, the length changes of all of the fiber bundles of the ACL were increased between 0° and 120° of knee flexion compared to the length changes occurring during passive flexion. In contrast to the behavior of the ACL, the length changes of all of the fiber bundles of the PCL were decreased between 0° and 120° compared to the length changes during passive flexion. The length changes of the MCL were increased but relatively low, <1.0 mm, for any of the three fiber bundles compared to the length changes during passive flexion. The length changes of the LCL were decreased between 0° and 120° of knee flexion, demonstrating behavior similar to the PCL during quadriceps loading. Both anatomical location and flexion angle had significant effects on the length changes of the ACL, PCL, and MCL during quadriceps loading. Of the 144 linear regression equations developed to model fiber bundle length, the coefficients of determination (square of correlation coefficient) of 137 of the equations were > 0.90, indicating that at least 90% of the variability in ligament length can be explained on the basis of differences in the magnitudes of the loads applied.

In the second study, the effects of the removal and surgical reconstruction of the ACL on the three-dimensional motions of the tibiofemoral and patellofemoral joints were investigated for flexion angles ranging from 0° to 90° in 15° increments in seven cadaveric knees. A bone-tendon-bone graft from the autogenous central one-third of the patellar ligament was used for the intraarticular reconstruction. The extraarticular reconstruction was performed in the manner of Mueller using the iliotibial band tenodesis. Knee loading was produced by extending the knee with quadriceps forces based on one-third of reported maximum voluntary isometric extension moments. The three-dimensional motions of the tibia and patella with respect to the femur were each characterized by six kinematics:​ three clinical rotations and three clinical translations. Compared to the intact knee, excision of the ACL resulted in significant increases in tibial valgus rotation and in anterior tibial translation. The intraarticular reconstruction returned normal tibiofemoral kinematics to the ACL-excised knee. The extraarticular reconstruction did not return normal tibiofemoral kinematics to the ACL-excised knee. Neither the removal nor the reconstruction of the ACL was found to significantly affect patellar flexion, patellar anteroposterior translation, or patellar proximodistal translation. Excision of the ACL resulted in significant increases in lateral patellar tilt and in lateral patellar shift. The intraarticular reconstruction returned normal patellofemoral kinematics to the ACL-excised knee. The extraarticular reconstruction failed to return normal patellar rotation or normal patellar tilt and increased patellar lateral shift.

In the third study, the effects of the removal and surgical reconstruction of the ACL on the contact characteristics of the patellofemoral joint were investigated at 30°, 60°, and 90° of knee flexion in seven cadaveric knees. A bone-tendon-bone graft from the autogenous central one-third of the patellar ligament was used for the intraarticular reconstruction. The extraarticular reconstruction was performed in the manner of Mueller using the iliotibial band tenodesis. Knee loading was produced by extending the knee with quadriceps forces based on one-third of reported maximum voluntary isometric extension moments. Fuji Prescale film was used to record patellofemoral contact pressure. Pressure intensity was measured using a high resolution optical scanner. The Fuji Pressure film and the scanning system were calibrated. Digital image processing techniques in conjunction with kinematic transformations were applied to analyze the contact prints. Interpretation of the processed patellofemoral contact information was performed using computer-aided-design schemes. In the intact knee, patellofemoral contact area increased by 137.2%, patellofemoral contact force increased by 214.3%, average patellofemoral contact pressure increased by 37.5%, and peak patellofemoral contact pressure increased by 40.7% as knee flexion increased from 30° to 90°. Compared to the intact knee, excision of the ACL caused significant decreases in patellofemoral contact area and in peak contact pressure on the medial facet of the patella. Intraarticular and extraarticular reconstruction of the ACL returned normal patellofemoral contact characteristics to the ACL-excised knee.