The Structure of the Enthesis

This study though is for tendon enthesis and we are more interested in ligament enthesis’.  But there should be a lot of similarities.

Optical anisotropy reveals molecular order in a mouse enthesis.

“Entheses are specialized biological structures that functionally anchor tendons {and ligaments} to bones. The molecular and supramolecular order of collagen and GAGs was determined for the collagen bundles of this enthesis. Based on a birefringence plot pattern as well as on metachromasy and linear dichroism after toluidine blue staining at pH 4.0, a similarity between the calcaneal tendon-bone enthesis and cartilage during ossification may be assumed. This similarity is assumed to favor the adequacy of this enthesis to support a compressive load. Considering that the collagen-proteoglycan complexes and the enthesis fibers themselves have a chiral nature, these structures could be acting via reciprocal signaling with the cellular environment of the enthesis.”

“Fibrous and fibrocartilaginous entheses are distinguished by the type of tissue at the attachment site”

“The attachment in an intact fibrocartilaginous ligament, which experiences compression, contains collagen types I, II and III, chondroitin 4-sulfate, chondroitin 6-sulfate, aggrecan and versican; however, the attachment in the disrupted ligament does not contain type II collagen and aggrecan”

“The collagen bundles in unstained, water-soaked sections from the calcaneal tendon exhibited intense birefringence{something to do with refraction}. The packing state of the collagen bundles increased, such that its maximum packing is attained around the calcaneal prominence. Fibrocartilage was detected in the proximity of the enthesis; collagen bundles gradually become less packed closer to the enthesis, where the bundles are separated by cartilage cells delimited by a birefringent extracellular, territorial matrix material”

“Chondrocytes were evident between the collagen bundles”

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