FAT EMBOLISM AND ACUTE HYPOTENSION DURING VERTEBROPLASTY IN SHEEP

Introduction: Vertebroplasty (VP) is a relatively new procedure to treat osteoporotic compression fractures of vertebral bodies. During this procedure polymethyl-methacrylate (PMMA) is injected into vertebral bodies. However there is the concern, that fat embolism (FE) and acute hypotension could occur as in a variety of other orthopaedic procedures. Aim: To investigate whether FE and acute hypotension are potential complications of VP using an animal model. Methods: In six sheep, 6.0 ml PMMA were injected unilaterally into the L1 vertebral body. Transœsophageal echocardiography was used to monitor the pulmonary artery for bone marrow and fat particles until 30 minutes post-operatively. Pulse, arterial and venous pressures were also recorded. The lumbar spine and the lungs were harvested post mortem. The histopathologic score, (percentage of lung fields occupied by intravascular fat globules as seen through the microscope), was calculated. Results: The first showers of echogenic material were visible approximately seven seconds after the beginning of the cement injection and lasted for about 2.5 minutes. The injection of bone cement caused a very rapid decrease in the heart rate after two seconds followed by a fall in the mean arterial pressure after 6.0 seconds. A maximum fall in heart rate was accompanied by a delayed fall in mean arterial pressure of 33.0 mmHg (P=0.0003) at 36seconds. The heat rate had returned to the baseline by 89 seconds and had increased by 10 beats/min (P=0.02) at 25 minutes. Mean arterial pressure had recovered by 209 seconds and was not different from the baseline at 25 minutes. Post mortem examination showed that no leakage of cement into the spinal cord had occurred. The histology revealed fat globules and bone marrow cells in the smaller and larger vessels throughout the lungs. The histopathologic score was 5.2 ± 0.9%. Conclusions: This study clearly showed that VP resulted in FE with a two-phase decrease in heart rate and arterial blood pressure. The first phase was probably due to an autonomic reflex and the second phase was due to the passage of fat emboli through the right heart and obstructing the lungs.