This study evaluated intra-articular injection of bone marrow–derived mesenchymal stem cells (BMSCs) to augment healing with microfracture compared with microfracture alone.
Ten horses (aged 2.5 to 5 years) had 1-cm2 defects arthroscopically created on both medial femoral condyles of the stifle joint (analogous to the human knee). Defects were debrided to subchondral bone followed by microfracture. One month later, 1 randomly selected medial femorotibial joint in each horse received an intra-articular injection of either 20 × 106 BMSCs with 22 mg of hyaluronan or 22 mg of hyaluronan alone. Horses were confined for 4 months, with hand walking commencing at 2 weeks and then increasing in duration and intensity. At 4 months, horses were subjected to strenuous treadmill exercise simulating race training until completion of the study at 12 months. Horses underwent musculoskeletal and radiographic examinations bimonthly and second-look arthroscopy at 6 months. Horses were euthanized 12 months after the defects were made, and the affected joints underwent magnetic resonance imaging and gross, histologic, histomorphometric, immunohistochemical, and biochemical examinations.
Although there was no evidence of any clinically significant improvement in the joints injected with BMSCs, arthroscopic and gross evaluation confirmed a significant increase in repair tissue firmness and a trend for better overall repair tissue quality (cumulative score of all arthroscopic and gross grading criteria) in BMSC-treated joints. Immunohistochemical analysis showed significantly greater levels of aggrecan in repair tissue treated with BMSC injection. There were no other significant treatment effects.
Although there was no significant difference clinically or histologically in the 2 groups, this study confirms that intra-articular BMSCs enhance cartilage repair quality with increased aggrecan content and tissue firmness.