Deep Vein Thrombosis
One of the major risks facing patients who undergo surgery in the lower extremities is a complication called deep vein thrombosis, a form of venous thromboembolic disease.
Deep vein thrombosis (DVT) refers to the formation of a thrombus (blood clot) within a deep vein, commonly in the thigh or calf.
Although venous thromboembolic disease can develop after any major surgery, people who have surgery on the lower extremities are especially vulnerable.
Three factors contribute to formation of clots in veins:
1. Stasis, or stagnant blood flow through veins
This increases the contact time between blood and vein wall irregularities. It also prevents naturally occurring anticoagulants from mixing in the blood. Prolonged bed rest or immobility promotes stasis.
Coagulation is encouraged by the presence of tissue debris, collagen or fats in the veins. Orthopaedic surgery often releases these materials into the blood system. During hip replacement surgery, reaming and preparing the bone to receive the prosthesis can also release chemical substances (antigens) that stimulate clot formation into the blood stream.
3. Damage to the vein walls
This can occur during surgery as Dr. Backe retracts soft tissues as part of the procedure. This can also break intercellular bridges and release substances that promote blood clotting.
Other factors that may contribute to the formation of thrombi in the veins include:
- Previous history of DVT or PE
- Metastatic malignancy
- Vein disease (such as varicose veins)
- Estrogen usage or current pregnancy
- Genetic factors
After hip surgery, thrombi often form in the veins of the thigh. These clots are more likely to lead to PE. After knee surgery, most thrombi occur in the calf. Although less likely to lead to PE, these clots are more difficult to detect.
Fewer than one third of patients with DVT present with the classic signs of calf discomfort, edema, distended veins, or foot pain.
Diagnosing DVT is difficult. Current diagnostic techniques have both advantages and disadvantages. The most commonly used diagnostic tests include venography, duplex or Doppler ultrasonography, and magnetic resonance imaging (MRI).
Both DVT and PE may be asymptomatic and difficult to detect. Thus, Dr. Backe focuses on preventing their development by using mechanical or drug therapies. Without this preventive treatment, as many as 80 percent of orthopaedic surgical patients would develop DVT, and 10 percent to 20 percent would develop PE. Even with these preventative therapies, DVT and subsequent PE remain the most common cause for emergency readmission and death following joint replacement.
Prevention is a three-pronged approach designed to address the issues of stasis and coagulation. Usually, several therapies are used in combination. For example, a patient may be fitted with graded compression elastic stockings and an external compression device upon admittance to the hospital; movement and rehabilitation begin the first day after surgery and continue for several months; anticoagulant therapy may begin the night before surgery and continue after the patient is discharged.
Early Movement and Rehabilitation
With hospital stays averaging just four to seven days after an arthroplasty on the lower extremity, early movement is imperative as well as beneficial. Physical therapy, including joint range of motion, gait training and isotonic/isometric exercises, usually begins on the first day after the operation. Pain relievers administered intravenously also facilitate early mobilization.
Mechanical preventatives are usually used in combination with other therapies. They include:
- Lower extremity exercises such as simple leg lifts, elevating the foot of the bed, and active and passive ankle motion to increase blood flow through the femoral vein.
- Graded compression elastic stockings, which are more effective in preventing thrombi formation in the calf than in the thigh.
Continuous passive motion, which is a logical treatment, but has not been proven effective in preventing the development of DVT.
- External pneumatic compression devices that apply pulsing pressures similar to those that occur during normal walking. They can help reduce the overall rate of DVT occurrence when used with other therapies, but they are difficult to apply and patient compliance is often a problem.
- In rare cases, a filter device may be placed in one of the large veins to prevent migration of clots.