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In addition to excellent proliferation and differentiation potential, mesenchymal stem cells possess immunomodulatory and anti-inflammatory functions by modulating T and B cells and inducing anti-inflammatory factors, which may enhance their regenerative power (Abumaree et al., 2012; Im, 2016). Compared with the numerous in vitro and in vivo studies published in this field, few  clinical studies have investigated the regeneration of articular cartilage and treatment of osteoarthritis.

Accordingly, considerable resources in terms of time and money have been poured into research on regeneration of articular cartilage and treatment of osteoarthritis. Adult stem cells, particularly mesenchymals, have emerged as a source for cartilage regeneration (Caplan, 2005).

Stem cell application for regeneration of articular cartilage and treatment of osteoarthritis

Unlike bone, which is self-regenerating tissue, the case of articular cartilage presents a dilemma in regeneration of damaged tissue. Articular cartilage has limited potential for self regeneration, and damage to articular cartilage eventually leads to the development and progression of osteoarthritis. The low intrinsic regeneration potential of articular cartilage has been attributed to the difficulty of progenitor cells to access the damaged site due to a lack of blood vessels and the inability of adjacent articular chondrocytes to migrate and produce matrix (Im, 2016; Vinatier et al., 2009)

In summary, most reported studies are uncontrolled ones. There are a few prospective, randomised studies. Bone marrow aspirate, bone marrow aspirate consentration  or culture-expanded mesenchymal stem cells were used for long bone nonunions, tibial osteotomies, distractionosteogenesis, spine fusion and fractures. Achievement of bony union and accelerated healing were reported using thoseion. To be commercialised, immediately available cell therapeutics would be needed. As mesenchymal stem cells do not provoke the host T-cell response, allogeneic implantation of stem cells will be available as an off-the-shelf product (Tasso and Pennesi et al., 2009; Tse et al.,2003). However, data from clinical reports using allogeneic mesenchymal cells for bone regeneration must be obtained for them to be considered a viable option for treating bone defects.

Of 11 patients with prior plating who had nonunion or delayed union of the distal tibial metaphysis and had additional percutaneous autologous bone marrow injection, nine attained bony union within 6 months of bone marrow injection, nine attained bony union within 6 months of bone marrow injection. Various aspirations and cell concentration techniques have been reported to increase the number of progenitor cells, with reported union rates ranging from 62,5% to 90% (Ateschrang et al.,2009; Dallari et al.,2007; Gan et al.,2008; Kitoh et al., 2007; Neen et al., 2006)

Another study showed that after percutaneous bone marrow injection (15-20 ml twice) in 20 cases of ununited fractures of long bone, 17 cases (85%) had successful union in 5 months (Garg et al., 1993)

Twenty patients who had delayed union were injected with bone marrow nonunion, with a mean of 9.65 months between initial surgery and marrow injection. Of the 20 fractures, 19 achieved clinical and radiological union, on average after 2.95 months (Connolly et al., 1991).