Nonuniform distribution of collagen density in human knee ligaments

Abstract

It is generally recognized that the mechanical properties of soft connective tissues are affected by their structural components. We documented collagen density distributions in human knee ligaments to quantify differences in density within and between these ligaments. In order to explain the variations in mechanical properties within and between different knee ligaments as described in the literature, the distributions of collagen density were correlated with these biomechanical findings. Human knee ligaments were shown to be nonhomogeneous structures with regard to collagen density. The anterior bundles of all ligaments contained significantly more collagen mass per unit of volume than the posterior bundles did. The percentage differences between the anterior and posterior bundles, in relation to the posterior bundles, were about 25% for the anterior cruciate ligament (ACL) and the collateral ligaments and about 10% for the posterior cruciate ligament (PCL). Along the cruciate ligaments, the central segments had higher collagen densities than did segments adjacent to the ligament insertions (ACL 9%, PCL 24%). The collagen density in the ACL was significantly lower than that in the other ligaments. These variations within and between the ligaments correlate well with the variations in mechanical properties described in the literature; however, other structural differences have to be taken into account to fully explain the variations in mechanical properties from the structural components.

The anterior cruciate ligament injury controversy: is “valgus collapse” a sex-specific mechanism?

“…Mommersteeg et al 58 found that orientation of loading at the knee is more critical in the cruciate ligaments compared with the collaterals and that loading orientation may affect the tensile stiffness of the ACL. Mommersteeg and colleagues59 also showed that collagen density is different between human ACL and MCL, with the ACL showing significantly lower collagen density compared with the MCL. Variations in collagen density have been shown to correspond to differences in Young’s modulus for the ACL and MCL 60.…”

Tissue Strain Reorganizes Collagen With a Switchlike Response That Regulates Neuronal Extracellular Signal-Regulated Kinase Phosphorylation In Vitro: Implications for Ligamentous Injury and Mechanotransduction

“…Facet capsular and other ligaments have varied fiber organization and density in different subregions where nerves have been identified and across different anatomic ligaments [1,[86][87][88][89]. The specific anatomy of a ligament can lead to varied macroscopic and microscopic mechanical responses especially for varied loading directions and under different loading rates.…”

Computational Modeling of Ligament Mechanics

“…Differences in the biochemical composition of ligaments has been studied in an effort to explain the observed material property inhomogeneities. 153,154 Frank et al 153 studied the normal rabbit MCL and found different levels of water content, glycosaminoglycan content and collagen concentration along the length of the ligament. Mommersteeg et al 154 showed that collagen density is nonuniformly distributed throughout human knee ligaments.…”