Characterization of Collagen Fiber Architecture in the Canine Diaphragmatic Central Tendon

The diaphragmatic central tendon (DCT), a collagenous soft tissue membrane, acts as a mechanical buffer between the costal and crural muscles. Its direction of mechanical anisotropy has been shown to correspond to the collagen fiber preferred directions [1]. These preferred directions were determined by gross histological examination, and were thus qualitative. In this work we quantified the collagen fiber architecture throughout the DCT using small angle light scattering (SALS). Helium-Neon laser light was passed through tendon specimens and the resultant scattered light distribution, which characterized the local collagen fiber architecture, was recorded with a linear array of five photodiodes. Throughout the DCT two distinct collagen fiber populations were consistently found. For each population three parameters were determined: 1) the preferred directions of collagen fibers, 2) the volume fraction (V_f) of fibers, 3) OI, an orientation index, which ranges from 0 percent for a random network to 100 percent for a perfectly oriented network. Vector maps were used to display results from 1) and 2), and showed a primary group (G1) going from the crural to costal muscles and a secondary one (G2) running perpendicular to G1. Comparisons of V_f between G1 and G2 showed that G1 contained about three times as many fibers as G2, a ratio similar to that found for the degree of mechanical anisotropy [1]. OI were found to be about 60 percent, indicating a high degree of orientation, with no significant regional or population differences (p<0.05). These quantitative results suggest that throughout the DCT the degree of mechanical anisotropy is controlled exclusively by V_f.