Fig. 5

Collagen organization is altered in tenotomized supraspinatus at 15D. a Representative images from the mid-belly of muscle cross-sections stained with Picosirius red viewed under brightfield microscopy. Collagen content was visualized using Picosirius red staining, and quantified using a threshold on ImageJ to calculate the percentage of pixels stained per area. No differences in total collagen content are evident between groups. b Collagen organization was assessed using Picosirius red-stained sections viewed under polarized light. Red represents more densely packed collagen that is perpendicular to muscle fibers, and green represents loosely packed collagen that is parallel to the fibers. When analyzed as a proportion to total colored pixels, supraspinatus muscle at 15D has a lower proportion of red pixels and greater proportion of yellow and green pixels compared to control, indicating altered collagen organization (decreased collagen density, crosslinking, and thickness) at 15D after tear. No differences were evident at 2D compared to control. Scale bar represents 50 μm. All data are presented as mean ± SD, p < 0.05. *, indicates statistical significance compared to control