In summary, mesenchymal cells injection has been applied to patients to treat osteoarthritis by itself or in conjunction with additional surgical procedures including microfracture, high tibial osteotomy or partial meniscectomy. Hyaluronic acid, corticosteroid, or platelet lysate were also used along with stem cells in some studies. In addition to several uncontrolled studies, a few controlled studies using injection of either bone marrow-derived mesenchymal stem cells or adipose stem cells reported regeneration of articular cartilage or meniscus as well as symptomatic improvement.