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Deep venous thrombosis is an unwanted complication associated with many invasive surgical procedures. Anticoagulation is commonly employed to reduce the risk of pulmonary emboli in the perioperative setting. Mechanical barriers traditionally have been used as an alternative when anticoagulation was contraindicated. In this case we demonstrate how a retrievable inferior vena cava filter added to anticoagulation can prevent a fatal pulmonary embolus.

Background
Nearly 200,000 cases of deep venous thrombosis (DVT) occur each year.¹ Dislodgement of a DVT with embolization to the pulmonary circulation results in a pulmonary embolism. One registry of 2454 patients diagnosed with a pulmonary embolism showed a three-month mortality rate of 17.5%.² Perioperative prophylactic low-molecular weight heparin, fondaparinux, vitamin K antagonists, or sequential pneumatic compression stockings have been recommended to reduce risk of DVTs. For two decades, permanent inferior vena cava filters (IVCF) have served as an alternative in preventing pulmonary embolism (PE) when anticoagulation was contraindicated.^3–5 This case graphically demonstrates the efficacy of a retrievable IVCF placed in a patient with a history of a DVT who was to undergo a total knee replacement.

Case report
A 55-year-old Caucasian male with no past medical history originally underwent arthroscopy for a meniscal tear in 2002. Postoperatively, he was diagnosed with a pulmonary emboli originating from a DVT. The patient then received six months of oral anticoagulation.

Two years later when a total knee replacement was required, a Günther Tulip Vena Cava Filter (GTF) (Cook Incorporated, Bloomington, Indiana) was inserted prior to surgery.

Following an uneventful total knee replacement, DVT prophylaxis with 30 mg enoxaparin injections was administered twice daily. The patient was taken to the endovascular lab several weeks later for retrieval of the GTF. An IVC gram surprisingly demonstrated a large filling defect within and around the GTF, representing a trapped embolus (Figure 1a). Thrombolysis was considered but was not initiated, due to the recent orthopedic procedure. The IVCF was left in place and full dose anticoagulation was begun. Four weeks later, the patient was brought to the endovascular lab for reevaluation of the trapped clot and possible thrombolysis. Digital subtraction angiography demonstrated marked improvement of the filter embolus (Figure 1b). The retrievable GTF was permanently left in the IVC, and the patient was to remain on lifetime anticoagulation.

Discussion
Over the past two decades IVCFs have prevented life threatening PE.⁶ Despite success in lowering PE mortality, complications from permanent IVCFs, which are undesirable for patients only transiently at high risk for thromboemboli, have been reported.⁷ Retrievable IVCFs, like the GTF, provide short-term protection while avoiding long-term morbidity.

Although technical experience with the GTF has grown, questions still remain as to the appropriate indications for use of the device. Few studies have examined the role of retrievable caval filter in preventing PE in high-risk surgical procedures. Rosner and associates evaluated the safety and efficacy of prophylactic IVCF placement in 22 high-risk patients who underwent major spine reconstruction. These authors concluded IVCF placement substantially decreased PE rates from 12% to 0%.⁸ Ferrell et al identified 6 patients, from a bariatric surgical registry of 586 patients, who were at high risk for thromboembolic complications and had an IVCF placed preoperatively.⁹ They concluded IVCF placement was feasible and safe for the morbidly obese individual undergoing gastric bypass, and should be considered for patients with risk factors for thromboembolic complications. Pieri et al placed 18 retrievable IVCF in patients who were to undergo invasive orthopedic surgery. Four of the 18 filters were prophylactically placed in patients at high risk for thromboembolic disease. These authors suggested that a retrievable IVCF was an ideal device to prevent pulmonary embolism in many clinical scenarios.¹⁰

In this case, we placed a retrievable IVCF for perioperative PE prophylaxis in a patient with a history of, but not current DVT, who was to undergo a high risk orthopedic procedure. If this patient did not have a prophylactic barrier present, a large, potentially fatal PE would have occurred. This case demonstrates graphically how a prophylactic retrievable IVCF can be life saving in a patient at risk for thromboembolic disease who is to undergo a procedure with known risk of DVT formation.

Conclusions
We recommend that during preoperative evaluation, prophylactic retrievable IVCF be considered for patients with known risk of forming thrombi, or for those undergoing procedures complicated by DVT formation, especially if anticoagulation is contraindicated.