Abstract
Introduction Vertebroplasty (VP), where vertebral bodies are injected with polymethylmethacrylate (PMMA) cement, is used to treat various spinal lesions. More recently VP has been used for augmenting osteoporotic vertebral bodies that have fractured or are at risk of fracture. Although the complication rate for VP is low, thermal damage caused by the exothermic curing of PMMA has been implicated.
The aim of this series of experiments was to measure the temperatures reached during VP using a sheep model. The cement volume effect and inter cement differences were assessed. Spinal cord monitoring was undertaken to monitor spinal cord function during this procedure to validate this for clinical use.
Methods In the in vivo experiment each of the lumbar vertebral bodies of 10 sheep were injected with one of two cements (Simplex & Vertebroplastic) and one of two volumes (3.0ml or 6.0ml). This was undertaken through an open approach in the lumbar vertebrae. While performing the in vivo experimental studies 6 of the sheep were concurrently monitored using epidural Motor Evoked Potentials (MEP’s).
Results There was a significant increase in the temperature at the bone cement interface. The mean peak temperature at the bone-cement interface was 49.5 C (3.0ml Simplex); 61.47 C (6.0ml Simplex); 42.1 C (DePuy 3ml) and 47.2 (DePuy 6ml).
Spinal cord monitoring showed that when PMMA was injected into the correct location within the vertebral body there was no change in amplitude of the evoked potentials. When significant leakage of PMMA occurred, there was a decrease in amplitude of MEP’s.
Discussion In this sheep model, using cement volumes similar to those used in human clinical practice, we were able to monitor temperature changes within the vertebral body at the bone cement interface. The temperature of the bone cement interface reached temperatures that are known to cause tissue necrosis.
Using epidural monitoring we were able to show that when PMMA is injected into the correct location within the vertebral body there is no change in amplitude of MEP’s.
The abstracts were prepared by Assoc Prof Bruce McPhee. Correspondence should be addressed to him at the Division of Orthopaedics, The University of Queensland, Clinical Sciences Building, Royal Brisbane Hospital, Herston, Brisbane, 4029, Australia.
