ABSTRACT
OBJECTIVES: Polymethylmethacrylate(PMMA) is often used to reconstruct the spine after total corpectomy, but the exothermic curing of liquid PMMA poses a risk of thermal injury to the spinal cord. The purposes of this study are to analyze the heat blocking effect of pre-polymerized PMMA sheet in the corpectomy model and to establish the minimal thickness of PMMA sheet to protect the spinal cord from the thermal injury during PMMA cementation of vertebral body. MATERIALS AND METHODS: An experimental fixture was fabricated with dimensions similar to those of a T12 corpectomy defect. Sixty milliliters of liquid PMMA were poured into the fixture, and temperature recordings were obtained at the center of the curing PMMA mass and on the undersurface(representing the spinal cord surface) of a pre-polymerized PMMA sheet of variable thickness(group 1:0mm, group 2:5mm, or group 3:8mm). Six replicates were tested for each barrier thickness group. RESULTS: Consistent temperatures(106.8+/-3.9degreesC) at center of the curing PMMA mass in eighteen experiments confirmed the reproducibility of the experimental fixture. Peak temperatures on the spinal cord surface were 47.3degreesC in group 2, and 43.3degreesC in group 3, compared with 60.0degreesC in group 1(p<0.00005). So pre-polymerized PMMA provided statistically significant protection from heat transfer. The difference of peak temperature between theoretical and experimental value was less than 1%, while the predicted time was within 35% of experimental values. The data from the theoretical model indicate that a 10mm barrier of PMMA should protect the spinal cord from temperatures greater than 39degreesC(the threshold for thermal injury in the spinal cord). CONCLUSION: These results suggest that pre-polymerized PMMA sheet of 10mm thickness may protect the spinal cord from the thermal injury during PMMA reconstruction of vertebral body.