Figure 2: Timeline of saline, PDRN, MSC, and PDRN with MSC injection. Normal saline (0.2 mL; group 1: SAL), PDRN (0.2 mL; group 2: PDRN), MSC (0.2 mL; group 3: MSC), and MSCs with PDRN (both 0.2 mL; group 4: MSC + PDRN) were injected under ultrasound guidance into the left shoulder subscapularis full-thickness tears 6 weeks after the tears were created. The analysis including gross morphology of tear site, histologic examination, and motion analysis was performed 4 weeks after injection of four different solutions. All rabbits were euthanized by carbon monoxide inhalation 4 weeks after injection of the different solutions. PDRN: polydeoxyribonucleotide; MSC: human umbilical cord blood-derived mesenchymal stem cell.