Synovial Sheath Cell Migratory Response to Flexor Tendon Injury: an Experimental Study in Rats

Purpose: We aimed to investigate the degree of participation of synovial sheath cells in the process of tendon healing by selective cell labeling and direct observation of migrational pathways.

Methods: We designed a novel rat animal model that employed vital dye staining of synovial sheath cells. The flexor digitorum profundus (FDP) tendon was removed from its sheath and vital dye was applied directly to the synovial sheath cells. A window was cut in the removed tendon before being returned to the sheath, thus placing a tendon injury adjacent to the labeled synovial sheath cells. The synovium remained intact at all times, and labeling was confirmed to be localized to the synovium. The migrational response of the synovial sheath cells to the tendon injury was observed by harvesting the tendons at 1, 3, 5, and 7 days (n = 6 for each time period) after injury and assessing tendon response with frozen sections under ultraviolet microscopy.

Results: Labeled synovial sheath cells were observed within the substance of the healing tendon 24 hours after injury, with numbers increasing with time for up to 5 days, but decreasing by day 7.

Conclusions: This study confirms that in the rat model synovial sheath cells move into the healing tendon area and then migrate into the tendon core.