A quantitative comparison of morphological and histological characteristics of collagen in the rabbit medial collateral ligament

Collagen fiber is one of the critical factors in determining mechanical properties of ligaments and both the morphological and histological characteristics of collagen have been widely studied. However, there was still no consensus about whether the morphological characteristics of collagen correlated with its histological characteristics in physiological ligaments. Rabbit medial collateral ligaments (MCLs) were measured under a transmission electron microscope and a polarized light microscope plus picrosirius red-staining to obtain the distributions of collagen fibril diameters and types at different anatomical sites of rabbit MCLs, respectively. The correlation between the fibril diameter and type was determined by a correlation analysis. The collagen fibril diameters at the different anatomical sites had different distributions (unimodal or bimodal) and mean fibril diameters were found to increase significantly from the anterior part to the posterior part (P = 0.0482) as well as from the proximal to the distal sections (P = 0.0208). Type I collagen in the core portion of MCLs was significantly less than at the other four peripheral areas (P < 0.005) but no significant variation was found in each respective portion (P > 0.05). The low coefficient in the correlation analysis (r = 0.3759) demonstrated collagen fibril diameters had no correlation with collagen types. This may provide a new view of collagen types in studying the mechanical behavior of ligaments.