Introduction: Vertebroplasty using polymethylmethacrylate (PMMA) is an established technique in the treatment of osteoporotic fractures of the vertebra. Complications of vertebroplasty associated with PMMA leakage can include damage to the spinal cord. Previous studies have sought to investigate thermal changes in the paravertebral region, but used smaller volumes of cement than are used clinically1, or used in vitro experimental techniques.2 We have designed an in vivo sheep model to investigate the thermal changes after injection of clinically relevant volumes of PMMA, and to measure change in cord function associated with PMMA extrusion.
Methods: Five sheep were anaesthetised and 1.0ml of PMMA was injected into the spinal canal at the L1 level, with measurement of the temperature by thermocouple. The L2 to L5 vertebral bodies were then exposed and 9 thermocouples placed at points in and around the vertebra (superior and inferior endplate, disc above and below, central body, posterior wall, and spinal canal) to measure paravertebral temperature for a 10- minute period after injecting 6.0mls of PMMA. All animals were then humanely euthanased, and the T12 to L2 vertebrae harvested to examine the effect of temperature on the vertebral body and spinal cord using light microscopy.
Results: The experiments showed significant increases in the paravertebral temperature, especially at the end-plates (mean temperature 51.7°C, mean increase in temperature +16°C). This is contrary to studies using small cement volumes or in vitro conditions. Intradiscal and posterior wall temperature did not significantly rise. Spinal canal temperature reached a mean 75.4°C in the presence of “extruded” cement. Microscopic examination showed thermal damage to the spinal cord.
Discussion: The experiments indicate that neurological complications associated with vertebroplasty are likely to be thermally mediated, and that the analgesic effects of vertebroplasty are likely to be, at least in part, due to thermal damage to endplate neurological structures.
