Pathogenesis and clinical relevance of bone marrow embolism in medullary nailing — demonstrated by intraoperative echocardiography

For the clarification of pulmonary impairment after medullary nailing of femoral fractures, the intramedullary pressure in the femoral cavity during the operative procedure was investigated. In addition, an intraoperative transoesophageal echocardiography was performed which revealed two phenomena occurring once the intramedullary pressure had increased: snow-flurry and configured emboli. An experimental study in sheep was performed in order to define the substrata of the sonographic echoes. The level of intrafemoral pressure which would result in bone marrow intravasation and the substrata of the echocardiographic echoes were studied in sheep by applying pressure to the femoral cavity. Sonography of the distal vena cava by laparotomy and macroscopic and histological investigation of the venous blood received throughout a proximal subdiaphragmal venotomy were undertaken. The intrafemoral pressure peaks correlated with the appearance of sonographic echoes in both patients and sheep. Snow-flurry is an indication of small amounts of bone marrow and already appears at an intramedullary pressure of 50 mmHg, which can easily occur during movement of non-stabilised fractures (values up to 90 mmHg were observed) — configured emboli consist of a core of bone marrow surrounded by thrombotic aggregate and only appeared at pressure increases of over 200 mmHg in the animal experiments. During medullary nailing in patients the intrafemoral pressure increases up to 200–600 mmHg in all reaming procedures. Configured emboli were seen in 8 of 20 patients being treated with reamed nailing. In five nailing procedures performed using the unreamed technique, no pressure increases greater than 70 mmHg and no configured emboli were observed. I.v. injected bone marrow results in pulmonary impairment. In non-stabilised fractures intramedullary pressure peaks constantly press small amounts of bone marrow into the circulation. This process helps to explain the benefit of early operations in multiply injured patients. During reaming large amounts of bone marrow pass into the circulation and may contribute to pulmonary damage and ARDS (adult respiratory distress syndrome) if cofactors are present (volume deficit, shock, thoracic trauma and preexisting restrictive lung disease). In patients with these conditions, nailing should be performed without reaming. In the case of a narrow medullary cavity in which nailing without reaming is impossible other forms of stabilisation (plate or exte