Femoral Nailing in a Porcine Model Causes Bone Marrow Emboli in the Lungs and Systemic Emboli in the Heart and Brain

Abstract

Background: Shaft fractures of the femur are commonly treated with intramedullary nailing, which can release bone marrow emboli into the bloodstream. Emboli can travel to the lungs, impairing gas exchange and causing inflammation. Occasionally, emboli traverse from the pulmonary to the systemic circulation, hindering perfusion and resulting in injuries such as heart and brain infarctions, known as fat embolism syndrome. We studied the extent of systemic bone marrow embolization in a pig model. Methods: Twelve anesthetized pigs underwent bilateral intramedullary nailing of the femur, while 3 animals served as sham controls. Monitoring included transesophageal echocardiography (TEE), pulse oximetry, electrocardiography, arterial blood pressure measurement, and blood gas and troponin-I analysis. After surgery, animals were monitored for 240 minutes before euthanasia. Post mortem, the heart, lungs, and brain were biopsied. Results: Bone marrow emboli were found in the heart and lungs of all 12 of the pigs that underwent intramedullary nailing and in the brains of 11 of them. No emboli were found in the sham group. The pigs subjected to intramedullary nailing exhibited significant hypoxia (PaO2/FiO2 ratio, 410 mm Hg [95% confidence interval (CI), 310 to 510) compared with the sham group (594 mm Hg [95% CI, 528 to 660]). The nailing group exhibited ST-segment alterations consistent with myocardial ischemia and a significant increase in the troponin-I level compared with the sham group (1,580 ng/L [95% CI, 0 to 3,456] versus 241 ng/L [95% CI, 0 to 625] at the 240-minute time point; p = 0.005). TEE detected emboli in the right ventricular outflow tract, but not systemically, in the nailing group. Conclusions: Bilateral intramedullary nailing caused bone marrow emboli in the lungs and systemic emboli in the heart and brain in this pig model. The observed clinical manifestations were consistent with coronary and pulmonary emboli. TEE detected pulmonary but not systemic embolization. Clinical Relevance: Femoral intramedullary nailing in humans is likely to result in embolization as described in our pig model. Focused monitoring is necessary for detection of fat embolism syndrome. Absence of visual emboli in the left ventricle on TEE does not exclude the occurrence of systemic bone marrow emboli.

Femoral nailing associated with bone marrow emboli in pigs induced a specific increase in blood IL-6 and broad inflammatory responses in the heart and lungs

“…The 12 animals undergoing intramedullary nailing have been described in detail previously, including the deposition of fat emboli in the lung and the heart ( 14 ).…”

“…Included pigs were specific pathogen-free Norwegian landrace pigs with an average weight of 27 (SD 4) kg, of which 12 underwent intramedullary reaming and nailing, four intravenous injection of autologous bone marrow, and four were sham-operated controls. The 12 pigs undergoing intramedullary nailing has been published recently, with data on fat emboli deposited in lung, heart and brain ( 14 ). Blood and tissue samples from these animals were used for analyses in the present study.…”

“…The animals were handled as previously described ( 14 ). Briefly, the pigs were anesthetized using intramuscular azaperone, ketamine, and intravenous pentobarbital until endotracheal intubation was achieved.…”

“…Consequently, we aimed to examine the scope of inflammation induced by intramedullary nailing of the femur in a porcine model. We recently reported bone marrow emboli to the lungs and heart after femoral nailing in 11 of 12 animals studied ( 14 ). In the present study we investigated the systemic response in blood and local inflammatory responses in lung and heart, with emphasis on complement activation and cytokine release in these animals.…”