APC-resistance is a risk factor for postoperative thromboembolism in elective replacement of the hip or knee - A prospective study

Postoperative venous thromboembolic complications are commonly seen after t otal replacement of the hip or knee. Recently, an inherited defect with res istance to the anticoagulant activity of activated protein C (APC-resistanc e) has been detected. APC-resistance seems to be a common risk factor. espe cially in Sweden and it increases the propensity for venous thrombosis, Thi s study assesses the prevalence of APC-resistance in a general population a nd its clinical significance for patients undergoing surgery associated wit h a high risk of thromboembolic complications. In a prospective cohort stud y? we analysed for APC-resistance in 645 consecutive patients before electi ve replacement of the hip or knee at 3 hospitals in southern Sweden. Thromb oprophylaxis with LMWH-heparin was given to all patients throughout the hos pitalisation period. We recorded events of clinical thromboembolism for 3 m onths postoperatively. Venography, ultrasonography or pulmonary scintigraph y was requested by the clinicians according to the existing routines, i.e. only patients with symptoms of thromboembolism were examined. A thromboembo lic complication was registered in 20(3.1%) patients. Fifty per cent of the venous thrombi had a proximal location. Only 0.3% of the patients had veri fied pulmonary embolism. APC-resistance was found in 14.1% of the patients, of whom 9.9% had experienced postoperative thromboembolism compared with 2 .0% of the patients without APC-resistance (p <0.0007). We conclude that AP C-resistance is a frequent risk factor for symptomatic postoperative deep v enous thrombosis with an estimated relative risk of 5.0 (95% confidence int erval: from 1.9 to 12.9) in elective replacement of the hip or knee.