The Role of Pmma Bone Cement Within Osteoporotic Bone-Thermal Injury, Permeability and Mechanical Properties

Vertebroplasty, the injection of polymethylmethacrylate (PMMA) into fractured vertebral bodies, has been widely used to treat osteoporotic compression fracture. It is an emerging surgical procedure to reinforce the bone structure of osteoporotic vertebrae by filling the porous cancellous bone with bone cement. Neurologic deficit after vertebroplasty have been reported. The possible causes of neurologic deficit after intraspinal leak of bone cement include thermal injury and mechanical compression to the spinal cord. Bone cements polymerize by radical-initiated addition reactions of monomer (liquid) and polymer (powder). The heat release during polymerization is a concern as it may cause thermal damage to the osseous tissue within the vertebral body and the surrounding soft tissues. Ideal bone cement for vertebroplasty should fit three criteria: 1) diminishing thermal damage, 2) maintaining suitable permeability and increasing working time, 3) maintaining mechanical strength. The current three-year study is thus designed to achieve the three ideal criteria. The maximal polymerization temperature of bone cement can be reduced by cooling bone cement and, therefore, diminishing thermal damage in vertebroplasty. This study will compare two methods to cool bone cement: 1) pre-cooling method: lowering the temperature before mixing, and 2) ice-water bath method: lowering the temperature after mixing. However, the influence of cooling temperature on thermal damage, injection permeability of bone cement, the working time and mechanical strength remained uncertain. Many factors affect the reaction of polymerization of polymethylmethacrylate and, therefore, the maximal polymerization temperature, injection permeability and mechanical properties of bone cement. A surgeon may change the temperature of bone cement to enhance the clinical applicability and safety of vertebroplasty. The aim of the present study is therefore to develop more accurate temperature control of bone cement during vertebroplasty. The optimal temperature control method will be developed in this study. The data will also reveal the influence of cooling temperature on the thermal damage, injection permeability and mechanical strength of bone cement. The contents of this three-year study are summarized as follows: A. The first-year study: Cooling Bone Cement in Cement Leakage Model Porcine vertebrae model for vertebroplasty with cement leakage established in our previous study will be used. Bone cements are prepared by two different cooling methods (pre-cooling and ice-water bath). Porcine vertebrae immersed in 37-degree saline to mimic the condition in human spine. The posterior cortex, foramen, center of vertebral body and anterior cortex are selected for temperature measurement of vertebroplasty. Peak temperature, net temperature changes and time required to reach the peak temperature will be recorded. We hope to prove that optimal temperature control of bone cement can diminish thermal damage, even if there is leakage. B. The second-year study: Injection permeability of Cooling Bone Cement Three types of commercially available test blocks are used to mimic different degrees of osteoporotic bone. Uniform infiltration experiments on isolated cores of osteoporotic bone (test bone block) are conducted, using a custom-built infiltration device. Bone cements are prepared by two different cooling methods. Permeability-versus-time chat during polymerization is examined. We hope to prove that optimal permeability and increase of working time can be achieved by temperature control of bone cement. C. The third-year study: Mechanical test and Porosity observation of Cooling Bone Cement Compression test and porosity observation of cooling bone cement will be conducted. Bone cements are prepared by two different cooling methods. The influence of cooling bone cement on mechanical properties and voids content will be investigated.

Project ID:PB10107-1748
External Project ID:NSC101-2221-E182-010