Hydroxyapatite-Based Biomaterials Versus Autologous Bone Graft in Spinal Fusion: An In Vivo Animal Study.

STUDY DESIGN: An in vivo study was designed to compare the efficacy of biomimetic magnesium-hydroxyapatite (MgHA) and of human demineralized bone matrix (HDBM), both dispersed in a mixture of biomimetic MgHA nanoparticles, with that of an autologous bone graft. OBJECTIVE: The objective of this study was to evaluate 2 new bone substitutes as alternatives to a bone autograft for spinal fusion, determining their osteoinductive and osteoconductive properties, and their capacity of remodeling, using a large animal model. SUMMARY OF BACKGROUND DATA: Spinal fusion is a common surgical procedure and it is performed for different conditions. A successful fusion requires potentially osteogenic, osteoinductive, and osteoconductive biomaterials. METHODS: A posterolateral spinal fusion model involved 18 sheep, bilaterally implanting test materials between the vertebral transverse processes. The animals were divided into 2 groups: 1 fusion level was treated with MgHA (group 1) or with HDBM-MgHA (group 2). The other fusion level received bone autografts in both groups. RESULTS: Radiographical, histological, and microtomographic results indicated good osteointegration between the spinous process and the vertebral foramen for both materials. Histomorphometry revealed no significant differences between MgHA and autologous bone for all the parameters examined, whereas significantly lower values of bone volume were observed between HDBM-MgHA and autologous bone. Moreover, the normalization of the histomorphometric data with autologous bone revealed that MgHA showed a significantly higher value of bone volume and a lower value of trabecular number, more similar to autologous bone than HDBM-MgHA. CONCLUSION: The study showed that the use of MgHA in an ovine model of spinal fusion led to the deposition of new bone tissue without qualitative and quantitative differences with respect to new bone formed with autologous bone, whereas the HDBM-MgHA led to a reduced deposition of newly formed bone tissue. LEVEL OF EVIDENCE: N/A.

Long-term results following cranial hydroxyapatite prosthesis implantation in a large skull defect model.

BACKGROUND: A large skull defect may occur after different events such as trauma, tumor resection, and vascular injuries. There is still some doubt about the best material to use for reconstruction. Hydroxyapatite ceramic is one of the materials in use, and its biocompatibility and osteoconductivity are well established. This study evaluated the interaction of a commercial hydroxyapatite custom-made prosthesis implanted in a large skull defect, to assess its osteointegration and its habitability with newly formed bone over time. METHODS: Ten sheep underwent craniectomy and reconstruction of the skull defect with a porous hydroxyapatite cranial prosthesis. The animals were divided into two groups: animals in group A were euthanized after 6 months and animals in group B were euthanized after 12 months. At the end of the experimental periods, each implant was evaluated macroscopically and radiologically, and analyzed by micro-computed tomography, histology, histomorphometry, and microhardness techniques. RESULTS: During the study, no adverse events occurred, and there was no evidence of inflammation or negative tissue reactions. Histology and histomorphometry showed new bone formation inside the implant in both experimental periods; newly formed bone had increased significantly (p < 0.05) by over 300 percent between 6 and 12 months. Three-dimensional micro-computed tomographic analysis showed new bone formation and material remodeling. Microhardness analysis indicated that the mineralization process and the mechanical properties of newly formed bone were not altered. CONCLUSIONS: The hydroxyapatite prosthesis showed its osteoconductivity and good biocompatibility. A low rate of fibrous tissue formation and a high rate of bony regeneration were found.

Orderly osteochondral regeneration in a sheep model using a novel nano-composite multilayered biomaterial.

The objective of this article was to investigate the safety and regenerative potential of a newly developed biomimetic scaffold when applied to osteochondral defects in an animal model. A new multilayer gradient nano-composite scaffold was obtained by nucleating collagen fibrils with hydroxyapatite nanoparticles. In the femoral condyles of 12 sheep, 24 osteochondral lesions were created. Animals were randomized into three treatment groups: scaffold alone, scaffold colonized in vitro with autologous chondrocytes and empty defects. Six months after surgery, the animals were sacrificed and the lesions were histologically evaluated. Histologic and gross evaluation of specimens showed good integration of the chondral surface in all groups except for the control group. Significantly better bone regeneration was observed both in the group receiving the scaffold alone and in the group with scaffold loaded with autologous chondrocytes. No difference in cartilage surface reconstruction and osteochondral defect filling was noted between cell-seeded and cell-free groups. In the control group, no bone or cartilage defect healing occurred, and the defects were filled with fibrous tissue. Quantitative macroscopic and histological score evaluations confirmed the qualitative trends observed. The results of the present study showed that this novel osteochondral scaffold is safe and easy to use, and may represent a suitable matrix to direct and coordinate the process of bone and hyaline-like cartilage regeneration. The comparable regeneration process observed with or without autologous chondrocytes suggests that the main mode of action of the scaffold is based on the recruitment of local cells.