Geneviève Guillemin

Experimental vertebroplasty using osteoconductive granular material.

STUDY DESIGN Osteoporotic human cadaveric thoracic vertebral bodies and vertebral bodies from mature sheep were used as model systems to assess coral resorption and new bone formation after injection of coral granules. OBJECTIVE To evaluate the use of natural coral exoskeleton, an osteoconductive material, for the filling of vertebral bodies. SUMMARY OF BACKGROUND DATA Percutaneous injection of polymethylmetacrylate (PMMA) is often proposed for prophylactically stabilizing osteoporotic vertebral bodies at risk for fracture or augmentation of vertebral bodies that have already fractured. Recently, the possibility of using osteoconductive materials in granular formulation was assessed in pilot studies. METHODS As a first step, the possibility of injecting coral granules percutaneously within osteoporotic human cadaveric thoracic vertebral bodies was assessed. As a second step, cavities were drilled into vertebral bodies of 10 mature ewes and were either left empty (control group) or filled with coral alone (CC) or coral supplemented with fibrin sealant (CC+FS). Quantitative evaluation of coral resorption and new bone formation was made 2 months and 4 months after implantation. RESULTS The distribution of coral granules injected into human cadaveric thoracic vertebral bodies was homogenous as assayed radiographically. In the experimental animal model, osteogenesis was increased in cavities filled with coral in comparison with cavities left empty at both 2 months and 4 months (P < 0.005 and P < 0.02, respectively). Surprisingly, supplementation of coral with a fibrin sealant had no positive influence on osteogenesis (P < 0.0008 at 2 months; P < 0.002 at 4 months). In addition, it led to an increase in coral resorption by as soon as 2 months (P < 0.0008). CONCLUSION These results demonstrate the osteoconductivity of coral in granular form for vertebral filling. Interestingly, interconnectivity between adjacent bone trabeculae and newly formed bone was restored; however, its mechanical significance remains to be determined. Further investigations are needed to evaluate the efficacy of coral in osteopenic animals and in relieving pain.

Use of the induced membrane technique for bone tissue engineering purposes: animal studies.

Animal experiments using the induced membrane procedure for bone tissue engineering purposes have provided evidence that the membrane has structural characteristics and biologic properties that may be used for bone tissue engineering purposes. Clinically relevant animal models have demonstrated that standardized particulate bone constructs can be used to repair large bone defects using the procedure and that the osteogenic ability of these constructs partially approaches that of bone autografts.

Animal Models for Bone Tissue Engineering Purposes

To assess the efficacy of engineered tissues, it is necessary to have (1) appropriate large animal models that mimic the clinical setting and (2) relevant methods of monitoring the biofuntionality of these tissues. However, developing these tissue constructs is a step-by-step process in which numerous variables such as scaffold design, source of stem cells and mode of growth factor application have to be optimized. After an in vitro optimization phase, the use of small animal models to optimize these various parameters and sort out any teething problems is recommended before launching into large animal models. Depending on the experimental aims, engineered tissues can be transplanted into either ectopic sites (subcutaneously or intramuscularly) or orthotopic sites. In all these experimental studies, non invasive imaging methods (X-ray, magnetic resonance, in vivo fluorescence, ultrasound imaging methods, etc.) as well as detailed quantitative molecular and histological analyses have been used to monitor the in vivo behavior of the engineered constructs. In this chapter we take stock of the present state of the art in this field.