**4. Conclusion**

In summary, MSCs play an important role in embryonic development, postnatal growth, repair, and regeneration mechanisms, as well as in maintaining tissue homeostasis, and synovial membrane mesenchymal stem cells are a promising, easily available source. Despite relevant recent advances, challenges still remain on the use of MSCs as standard therapeutic options for clinical applications.

Although BM-MSCs remain the most studied source of MSCs, as they were the first to be characterized, SM-MSCs are an easily available source with proven enhanced chondrogenic, osteogenic, and myogenic differentiation ability. Nonetheless, their characterization, as established by the expression of specific cell surface markers, may be affected by interindividual heterogeneity and major differences in cellular marker expression profiles may be found in nonhuman species.

The most effective administration route for SM-MSC application *in vivo* remains to be defined and the genetic stability of the cells must be assured both *in vitro* and *in vivo*. Also, the biomechanics and secretory profile of these cells must be further studied, in order to comprehend the mechanism of regenerative capacity of these cells and secretion profile in signaling factors, growth factors, cytokines, and other bioactive molecules, and their role on chondrogenic as well as osteogenic and myogenic differentiation.

SM-MSCs present themselves as a promising source of MSCs that are becoming the targets of several research groups worldwide. Their application *in vivo* in preclinical and clinical trials is envisioned for the therapeutics of musculoskeletal disorders.
