Wakitani et al. applied bone marrow mesenchymal cells to repair human articular cartilage defects in osteoarthritic knee joints as an additional procedure to a high tibial osteotomy. In 24 knees, of 24 patients with knee osteoarthritis, culture-expanded mesenchymal stem cells embedded in collagen gel were transplanted into the articular cartilage defect in the medial femoral condyle and covered with autologous periosteum at the time of 12 high tibial osteotomies. The other 12 subjects served as cell-free controls. Although the clinical improvement was not significantly different, the arthroscopic and histological grading score was better in the cell-transplanted group than in the cell-free control group (Wakitani et al., 2002)