Rabillard M, Grand JG, Dalibert E, Fellah B, Gauthier O, Niebauer GW. Dr. Michael Rabillard, DVM, Department of Small Animal Surgery, Veterinary School of Nantes, Atlanpole - La Chantrerie, BP 40706, 44307 Nantes Cedex 3, France, Phone : + 33 2 40 68 76 72, Fax: + 33 2 40 68 77 73, E-mail: michael.rabillard@voila.fr. VCOT 2009 22 6 460-6 The aim of the study was to evaluate the bone healing properties of an osteopromotive platelet rich plasma (PRP) gel in combination with osteoconductive calcium phosphate (CaP) ceramic granules in a long-bone critical size defect in dogs. A standardised 2 cm long ulnar ostectomy was performed bilaterally in four dogs to compare new-bone formation by CaP matrix with and without association with PRP. Radiographic and histological evaluations were performed blindly. Radiographic evaluation was performed at three, six, nine, 12 and 16 weeks postoperatively. Quantitative measurements of new-bone formation were compared using statistical analysis. At explantation 16 weeks after surgery, no significant ossification was present, neither with CaP granules alone nor in association with PRP gel, and there was no difference of radiodensity between the groups. Qualitative histological evaluation demonstrated for both types of implants the presence of non-mineralised fibrous connective tissue around the CaP granules. New-bone formation was only present to a very small extent within the macropores of the CaP granules at the distal bone-implant interface. In our model which exhibited very limited osteoconduction, neither the CaP granules alone nor in association with PRP were sufficient to stimulate bone healing. In this canine model employing a critical size ulnar gap, the combination of CaP granules and PRP did not effectively promote bone regeneration.