Mesenchymal Stem Cells in a Clinical Trial to Heal Articular Cartilage Defects

The purpose of this study is to: * Compare the treatment efficacy of autologous mesenchymal stem cells (Mesenchymal Stem Cells) versus chondrocytes implanted in a commercial available scaffold in a human clinical trial. * Determine the effects of specific three months strength training program preoperatively to improve knee function and possible postpone the need of cartilage repair surgery. * Determine if degenerative changes occur in the knee joints following cartilage repair. This question will be investigated in the proposed clinical trial. * Determine the characteristics of patients treated either by surgery or by rehabilitation in a long-term follow-up (1, 5 years).