Development of a computer model to predict strains in the individual fibers of a ligament across the ligamentous occipito-atlanto-axial (C0-C1-C2) complex.

A fresh ligamentous occipito-atlanto-axial (C0-C1-C2) complex was appropriately prepared and serially sectioned into thin slices along the transverse planes. The bony outlines from these slices were digitized and assembled in the proper manner to obtain a three-dimensional model of the complex using the AutoCAD system. Various ligaments were identified on the model and strains in individual fibers of a ligament were predicted based on the principles of rigid body mechanics. The ligament behaviors in axial rotation, flexion, and extension modes were analyzed. The capsular ligament fibers were predicted to undergo strains in all modes. Furthermore, these ligaments experienced the largest strain among the ligaments analyzed. Fibers within a ligament were found to respond differently; some were more active than the others and some did not experience any strain at all. A differential behavior in the right and left side alar ligament fibers was also found in axial rotation. The transverse ligament was predicted to wrap around the dens during axial rotation. The strain within a fiber was found to be a function of the initial length (ligament laxity) and its distance from the center of rotation.