Histology. Hematoxylin-eosin sections show the improvement of tendon ultrastructure in control (A-C) and hMSC-treated (D-F) groups 2, 4 and 6 weeks after tendon injury. Better organization of the extracellular matrix was observed after hMSC treatment compared to the saline-treated tendons (Scores A-7, B-12, C-13, D-11, E-14, F 17). The formation of cartilage and bone was confirmed by collagen II staining, 6 weeks after injury (G,H). Mesenchymal stromal cells survived at the site of the lesion as confirmed by MTCO2 staining (I).