Quantitative analysis of collagen fibrils of human cruciate and meniscofemoral ligaments.

The ultrastructural anatomy of collagen fibril diameters in the cruciate and meniscofemoral ligaments, from four young human cadaver knees (mean age, 20 years, range, 17-22 years) was studied using transmission electron microscopy. Samples were harvested from the proximal, middle, and distal regions of the anterior and posterior cruciate ligaments, and the meniscofemoral ligament. Photomicrographs were taken and assessed quantitatively using image analysis software to determine the collagen fibril diameters and eccentricities, and the percentage of total cross sectional area occupied by collagen. The collagen fibril diameter for the anterior cruciate ligament was found to be largest in the distal region but it decreased as it moved proximally. The posterior cruciate ligament had an opposite trend because it decreased from the proximal to the distal region. For the meniscofemoral ligament, the fibrils of the middle region were larger than those of the proximal and distal regions. The percentage of total cross sectional area occupied by collagen, however, did not vary significantly between regions. Fibril eccentricity also varied little between ligament or location. The variability observed in fibril diameters may account for the different mechanical properties of the ligaments.