© 2011 Wichtig Editore - ISSN 1120-7000 Hip Int ( 2011 ; : 05 ) 616 - 622 21 616 INTRODUCTION Thermal injury and monomer toxicity associated with the use of polymethyl methacrylate (PMMA) bone cement remain causes for concern for surgeons using PMMA for cemented fixation and defect filling in arthroplasty surgery. The polymerisation of bone cement is an exo- thermic reaction in which a significant amount of thermal energy is generated. This heat must be dissipated by adjacent bone and soft tissues, and also possibly by the prosthesis. Whilst there is no definitive evidence regard- ing critical values or their durations, an increase in tem- perature of the bone to above 50˚C has been implicated with a reduced regenerative capacity (1) and above 56˚C with osteonecrosis (2). In vivo response of bone defects filled with PMMA in an ovine model Stephen McMahon 1 , Gabrielle Hawdon 1 , John Baré 2 , Yan Yu 3 , Nicky Bertollo 3 , William R. Walsh 3 1 Malabar Orthopaedic Institute, and Monash University, Melbourne - Australia 2 Melbourne Orthopaedic Group, Melbourne - Australia 3 Surgical and Orthopaedic Research Laboratories, University of New South Wales, Sydney - Australia ABSTRACT: The use of PMMA cement is common in arthroplasty for cemented fixation and defect filling. Concerns remain regarding effects of cement curing temperature on the viability of cancel- lous bone. In this study we filled surgically-created defects (mean volume 0.585±0.251mL) in the cancellous bone of the distal femur and proximal tibia of 6 sheep with PMMA and measured tem- perature changes in surrounding bone whilst the cement cured, using 3 thermocouples per defect. Animals were euthanised at 3 (n=3) and 12 (n=3) weeks postoperatively and the bone-cement interface assessed histologically. Despite mean maximum temperatures of 49.3±10.2°C (range: 40.9°C – 82.2°C) thermonecrosis was not a common histological feature at either timepoint. The exposure of bone to high cement temperatures in this study has not led to bone necrosis and/or tissue damage. KEY WORDS: Bone cement, PMMA, Thermonecrosis, Cemented fixation, Osteocyte lacunae Accepted: June 24, 2011 ORIGINAL ARTICLE Little and co-workers (3) demonstrated that the maxi- mum temperature experienced by the bone is dependent on the thickness of the cement mantle. Bone necrosis at the cement mantle interface may result in failure of pros- thetic fixation and subsequent aseptic loosening of the implant. Aseptic loosening of the femoral component and neck-of-femur fracture are recognised complica- tions of cemented resurfacing arthroplasty. This study examined in vivo temperature in cancellous bone adjacent to curing PMMA cement in surgically- created bone defects in an ovine model using thermo- couples implanted during the procedure and correlated the measured temperatures with volume of cement and with radiographic and histologic evidence of bony injury and necrosis. DOI: 10.5301/HIP.2011.8704