Background: Osteochondral injuries, involving damage to both cartilage and subchondral bone, require a biphasic regenerative approach. A previous study demonstrated that a biphasic implant, composed of a hydroxyapatite (HA) block for the bone layer and a scaffold-free synovial mesenchymal stem cell–derived tissue-engineered construct (TEC) for the cartilage layer, successfully repaired osteochondral defects in a rabbit model. To facilitate less invasive surgical application, the authors investigated alternative HA forms including granules and paste for use in the subchondral component for the biphasic implant. Hypothesis: Biphasic implants composed of TEC combined with either HA granules or HA paste would potentially achieve successful osteochondral repair, comparable to that of a conventional HA block–based implant. Study Design: Controlled laboratory study. Methods: Bilateral osteochondral defects (5 mm in diameter and 6 mm in depth) were created in the femoral grooves of rabbits and treated with a TEC combined with 1 of 3 HA forms: block, granules, or paste. Histological and biomechanical analyses were performed at 4, 8, and 24 weeks postimplantation (5 per group per time point). Results: The TEC/HA block group achieved complete osteochondral repair with stable maturation, and the repaired tissue demonstrated biomechanical properties comparable to native tissue at 24 weeks postimplantation. In contrast, the TEC/HA granule group showed early signs of repair that progressively deteriorated, resulting in significantly inferior structural and mechanical properties. The TEC/HA paste group supported subchondral bone repair but resulted in incomplete cartilage formation at 24 weeks postimplantation. Conclusion: The TEC/HA block implant showed superior histological and biomechanical outcomes compared with other HA forms. Therefore, further optimization of granular or paste formulation is required to possibly enhance the potential for arthroscopic or minimally invasive delivery of a biphasic implant. Clinical Relevance: This study highlights the potential of biphasic implants combining clinically available TEC and HA artificial bone for osteochondral repair. The biphasic implant can be easily prepared intraoperatively without specialized fabrication. Long-term observations revealed distinct repair patterns for each HA form, which may assist surgeons in selecting the optimal HA artificial bone form for effective and durable subchondral bone repair in osteochondral regeneration.
Shimomura et al. (2026) studied this question.