Overview
Deep venous thrombosis, or DVT, is a known complication of knee fractures. “Knee fractures” refer specifically to fractures of the distal femur, patella, or proximal tibia. These fractures are associated with increased clotting risk due to the fracture itself and to the subsequent treatment. Prolonged bed rest and immobilization leads to more of a risk of developing DVT. Prevention by early movement and DVT prophylaxis is generally believed to be the best treatment for DVTs.
Virchow’s Triad
Virchow’s triad refers to the conditions that occur in the veins that lead to increased risk for thrombosis. Endothelial damage, hypercoagulability, and venous stasis are the three components of Virchow’s triad. Endothelial damage refers to injury to the wall of the vein. Trauma, surgery, venapuncture (blood draws), chemical irritation, atherosclerosis, and indwelling catheters all can lead to vascular injury. Hypercoagulable state refers to a state of increased risk of clotting. Causes of a hypercoagulable state include malignancy (cancer), pregnancy, estrogen therapy/ birth control pills, trauma, surgery to the lower extremity, abdomen, pelvis, inflammatory bowel disease, nephrotic syndrome, sepsis (bacterial blood infection), and inherited or acquired thrombophilia. Circulatory stasis refers to conditions where there is poor movement of blood. This allows the blood to have an increased risk of clotting. Patients with atrial fibrillation, heart dysfunction, immobility, paralysis, venous insufficiency, and venous obstruction are all at increased risk for DVTs.
Knee Fractures
The knee is the articulation of the patella, tibia, and femur. Treatment of patella fractures is typically accomplished by immobilization, with or without surgery. Treatment of distal femur fractures depends on the degree of displacement and the specific patient. Non-displaced distal femur fractures are typically treated with surgery, however can be treated with casting and immobilization. Displaced distal femur fractures require surgery aimed at stable fixation to allow for early movement. Treatment of tibial plateau (proximal tibia) fractures depends on the level of displacement of fragments. Non-displaced fractures can be treated with a hinged fracture brace that allows for early range of motion and partial weight bearing. Surgery aims at restoring the anatomical alignment. Passive motion is performed from 0 to 30 degrees a few days after surgery. Progressive weight bearing is allowed. Overall patients with knee fractures do spend most of the day in bed, which leads to an increased risk of DVT.
Prophylaxis
DVT prophylaxis is indicated for any patient undergoing surgery or with a fracture that leaves them unable to bear weight and ambulate. Non-medication DVT prophylaxis is done with compression stockings–TEDs–and/or pneumatic sequential compression boots. The pneumatic sequential compression boots intermittently inflate and deflate to help propel venous blood from the leg.
Medication DVT prophylaxis is with either subcutaneous injection of heparin, fondaparinux, or low-molecular weight heparin (eg. lovenox). Some physicians will use coumadin (Warfarin) or aspirin instead.
According to a 2002 study by Dr. A. G. Turpie of Hamilton Health Sciences-General Hospital, 2.5 mg of fondaparinux sodium reduced the risk of DVT more than enoxaparin (a low molecular weight heparin) without increasing the risk of bleeding.
Dr. R. L. Schiff of McGill University in 2005 studied thromboprophylaxis and total knee replacement surgery and found that approximately 14 percent of patients on prophylaxis still developed DVTs. The study showed the importance of both chemical prophylaxis,early ambulation, and adjunct methods such as pneumatic compression to reduce the risk of DVT as much as possible.
The best form of prophylaxis is active movement as early as possible in the post-operative period. This gets the blood moving in the lower extremities.
Diagnosis of a DVT
The diagnosis of a DVT is made based on a clinical suspicion, lab tests, and radiographic imaging. Patients typically report pain greater in one leg than the other. There may be increased swelling on one side more than the other. The leg circumference may be increased on the side with the DVT. Patients may display calf tenderness when squeezed. Some patients have pain with dorsiflexion stretch of the gastrocnemius. Dorsiflexion of the ankle refers to when the ankle is moved so that the toes move closer to the shin bone.
Clinical suspicion leads the physician to consider ordering diagnositic tests. In a patient with no recent surgeries, a D-dimer level if elevated can lead to an increased clinical suspicion for DVT. Most clinicians start with ordering a venous ultrasound of the extremity. Contrast venography, where the veins are cannulated and dye is injected and imaged with fluoroscopy, is very diagnostic. An MRI with gadolimium contrast is proving to be very good at finding DVTs.
Treatment
Treatment of a DVT involves proper anti-coagulation to prevent another thrombosis or from allowing the thrombosis to grow in size. Injectable medications are aimed at inhibiting the coagulation cascade. Heparin, low-molecular weight heparin, and fondaparinaux are all injectable medications. The treatment of DVTs with injectables requires a higher dose per day than for prophylaxis. Oral medications such as coumadin are aimed at antagonizing vitamin K to not allow for coagulation. Coumadin initially makes a patient hypercoagulable (easier to clot) therefore treatment typically starts with simultaneous use of an injectable and coumadin as coumadin becomes therapeutic, the injectable is discontinued.
About this Author
Gregory Waryasz is a graduate of Boston College and an M.D. candidate for May 2010 at Tufts University School of Medicine. He will be starting an orthopaedic residency at Brown University/Rhode Island Hospital in June of 2010. He is certified as a strength and conditioning specialist (CSCS) through the NSCA.
