RRJoVST (2017) 3-6 © STM Journals 2017. All Rights Reserved Page 3 Research & Reviews: Journal of Veterinary Science and Technology ISSN: 2319-3441 (Online), ISSN: 2349-3690 (Print) Volume 6, Issue 3 www.stmjournals.com Histopathological Evaluation of Polymethyl Methacrylate and Hydroxyapatite Implants for Fracture Healing in Rabbits K. Harsha Vardhan, V. Devi Prasad*, Makkena Sreenu, N. Syaamasundar Department of Veterinary Surgery and Radiology, NTR College of Veterinary Science, Gannavaram, Andhra Pradesh, India Abstract Experimentally created mid diaphyseal fractures in 24 rabbits were treated by intramedullary pinning with K-wires, polymethyl methacrylate (PMMA) implants and intramedullary pinning after stuffing with hydroxyapatite (HA) paste and the histopathological changes were recorded. Healing process was not progressive, in control group, as indicated by presence of only a few osteocytes in the matrices, discontinuity in the epithelial layer and extensive vacuolation with occasional presence of giant cells. In PMMA group, healing pattern by endochondral method of ossification was evident by day 30 and day 60, normal structure of bone with remarkably high osteoid formation and osteocytes proliferation were observed. In HA group, vacuolation and discrete presence of osteocytes separated by interlacing trabeculae when compared to the other two groups were more pronounced. By day 60, endosteal vascularization could be depicted under high power. To conclude, of all the three groups healing was better in PMMA group when compared to the other two groups. Keywords: polymethyl methacrylate (PMMA), hydroxyapatite (HA), endosteal vascularization, endochondral ossification, vacuolation *Author for Correspondence E-mail: professorprasad@yahoo.com INTRODUCTION Fracture is defined as a discontinuity in hard tissues such as bone and cartilage. The fracture in animals invariably causes pain and suffering to them, apart from loss of function of' the affected limb. The methods to address fractures in different species vary significantly. In the recent years, there has been a trend to use biodegradable and bio- absorbable implants for fracture healing in animals. As polymethyl methacrylate (PMMA) can be molded to different shapes and sizes, it was used for the repair of fractures. Hydroxyapatite (HA) is a biocompatible implant material having osteoconductive capacity and is known for its passive support for neovascularization. In the present paper, the efficacy of PMMA and HA was shown in terms of histopathological features. MATERIALS AND METHODS The experiment was conducted in 24 rabbits divided into three groups of eight each. In all the animals, diaphyseal fractures were created using a circular wire saw and were immobilized with K-wires (n=8; Group- I), PMMA implants (n=8; Group, II) and HA quoted implants (n=8; Group, III). The stainless-steel K-wires of 1–2 mm diameter were employed to immobilize the fracture fragments through standard protocol. In the second group, the PMMA implants resembling K-wires were prepared by mixing the powder with liquid copolymer and were used to immobilize the fracture fragments (Figure 1). It was smeared in the groove of a mold under low temperature and the implant was used for immobilizing the fracture fragments. In the third group, HA paste was stuffed into the medullary cavity of the fragments and K-wires were used for fixation (Figure 2). Two rabbits from each group were euthanized using Thiopentone Sodium by intravenous route till effect and the fractured femur was collected for gross and histopathological evaluation. The bone samples were made free from the soft tissue. After total decalcification, bone samples were subjected for routine paraffin embedding technique and the sections were stained by the Hematoxylin-Eosin staining technique as per the method of Singh and Sulochana [1].