Anterior Cruciate Ligament Biomechanics, Computational Modeling of Mechanical Behavior and Injury Risk

Knee joint involves interactions from various structures such as cartilage, bone, muscles, ligaments, tendon, as well as neural control. Anterior cruciate ligament (ACL) tears are one of the most frequent soft tissue injuries of the knee. A torn ACL leaves the joint unstable and at risk for further damage to other soft tissues manifested as pain, dislocation, and osteoarthritis. This injury is quite common in sports such as basketball, soccer and football. Females often tear their ACL 2-8 times more frequently than their male counterparts. An ACL injury can be devastating and significantly increases the athlete\u27s risk for osteoarthritis long term. While many advances have been made in terms of surgical and rehabilitation treatments for ACL injured patients, long term outcome studies show that these patients are at a high risk for developing knee osteoarthritis 10-15 years after ACL injury, regardless of the treatment. Currently, the mechanism of non-contact ACL injury is not well understood. Therefore, the knowledge of the ACL biomechanics is of importance in various clinical scenarios, since it would be instrumental in its understanding of structure and function which are necessary to diagnose and prevent ACL injury. This dissertation further investigates four areas; demographic studies which relate anatomical features to ACL injury, computer aided diagnostic tools which can be used to diagnose a common complication with ACL injury, computational simulations of ACL biomechanics using representative gait data, and finally risk of injury assessments. Magnetic resonance images (MRIs) of 32 patients with ACL tears and 40 patients who did not have ACL tears were evaluated from a physician group practice. Digital measurements of femoral condyle length, femoral notch width, ACL width in the frontal and sagittal plane, and the ACL length in the sagittal plane were taken in both groups. Empirical data correlations were performed and trends identified. Similarly, a sample from the Fels gait data was a larger subset which consists of 178 healthy volunteers, out of which 99 were females and the remaining were males. Finite element (FE) analysis has become an increasingly popular technique in the study of human joint biomechanics, as it allows for detailed analysis of the joint/tissue behavior under complex, clinically relevant loading conditions. A wide variety of modeling techniques have been utilized to model knee joint ligaments. However, the effect of a selected constitutive model to simulate the ligaments on knee kinematics remains unclear. Computational knee joint models were based on patients\u27 medical images. Using a sample from Fels Longitudinal study, loads were determined from the gait profile of healthy volunteers and the stress distributions on the ACL were determined. The anatomical representation of the ligament make it feasible to determine stress distribution across the ligament which in turn provide valuable information about the mechanism of ligament injury. 3D anisotropic hyperelastic model was found to simulate physiological behavior of human knee. Females have significantly greater abduction angles (p \u3c 0.005). Similarly, males have significantly larger adduction angles than the females (p\u3c0.05). In this study, the peak ACL force observed during normal walking was less than ½ BW. A combination of tibial and valgus rotations of the tibia had resulted in a Von Mises stress on the ACL as high as 62 MPa which is indicative of ACL injury. A linear relationship was determined to investigate the relationship between NWI and width of the ACL. This may suggest that NWI plays no significant role in the causes for ACL injury. Sensitivity analysis had shown that there is a linear relationship between the forces applied and risk for ACL injury