Bone marrow-derived cell concentrates have limited effects on osteochondral reconstructions in the mini pig

This study investigates the effects of seeding a chondrogenic and osteogenic scaffold with a bone marrow-derived cell concentrate (BMCC) and reports the histological and mechanical properties 3 months after implantation in the miniature pig. Twenty defects (7×10 mm) were created in the femoral condyles of 10 miniature pigs. The defects were left empty (E), filled with the grafted cylinder upside down (U) or with a combined scaffold (S) containing a spongious bone cylinder (Tutobone®) covered with a collagen membrane (Chondrogide®). In a fourth group, the same scaffolds were implanted but seeded with a stem cell concentrate (S+ BMCC). The animals were stained with calcein green after 2 weeks and xylenol orange after 4 weeks. After 3 months, the animals were sacrificed, and a mechanical analysis (Young's modulus), macroscopic, and histologic (ICRS Score) examination of the specimens was conducted. Young's modulus in the periphery was significantly lower for group E (67.5±15.3 kPa) compared with untreated controls (171.7±21.6 kPa, p<0.04). Bone defects were smaller in group S (10%±8%) compared with E (27%±7%; p<0.05). There was a trend toward smaller bony defects on comparing groups E and S+ BMCC (11%±8%; p=0.07). More red fluorescence was detected in group S+ BMCC (2.3%±1.1%) compared with groups E (0.4%±0.2%) and U (0.5%±0.2%, p<0.03). ICRS scores were higher for groups S (25.3±3.8) and S+ BMCC (26.2±5.2, p<0.01). In this animal model of osteochondral defects, stem cell concentrates enhance new bone apposition but fail to improve mechanical properties or histological appearance of cartilage regenerates in critical-sized defects.