To validate the widespread formation and to explore further, the possible inflammatory function of SECs, researchers collected ligament and tendon attachment samples from 60 cadavers, 35 male and 25 female, with a mean age of 84 years at death. 49 different entheses19 from the arms, 26 from the legs, and 4 from the spinal columnwere preserved for examination. To exclude cartilage degeneration as a trigger for synovial inflammation, 17 of the selected entheses were not immediately adjacent to joint cartilage. Each sample was studied for evidence of inflammatory cells and soft tissue microdamage, as well as for the composition of SECs.
At 82 percent of the entheses, the formation of a SEC was found. As expected, this occurred in entheses very close to joint cartilage, where the synovium was often part of the joint itself. However, a SEC was also detected in 47 percent of the sites separated from joint cartilage. For example, the SEC found at the Achilles tendon was formed with synovium that protruded from a cavity called a bursa, located a considerable distance from the ankle joint.
Joint insertions are sites of high mechanical stressing and the authors speculated that this could lead to damage within them, including their fibrocartilage This is exactly what the authors found. Degenerative changesat least one and sometimes severalwere detected on the soft tissue side of attachment sites. Most notably, cell clustering and/or fissuring was found in 76 percent of entheses. In 85 percent of SECs, the synovial component also showed evidence of mild inflammatory change. Finally, in 73 percent of the attachments, small numbers of inflammatory cells were present in the enthesis itself. Therefore the authors suggest that joint degeneration of fibrocartilage at insertions could trigger inflammation within SECs.
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