Sebastian Schellong

Die Venen der unteren Extremitäten werden durch die Fascia superficialis in ein oberflächliches und ein tiefes System geteilt. Sie sind in ihrem gesamten Verlauf durch Venae perforantes miteinander verbunden. Das Blut aus den oberflächlichen Venen wird durch zwei Sammelstämme, die Vena saphena magna und die Vena saphena parva, in die tiefen Venen abgeleitet. Die tiefen Venen sind Begleitvenen der Arterien. Die Zirkulationsrichtung des Blutes in den Venen wird durch Klappen bestimmt, deren Anzahl variabel ist. Die Venen sind von einer Venenscheide umgeben, innerhalb deren sie verschiebbar sind. Die tiefen Venen des Unterschenkels werden in drei paarig angelegte Gruppen eingeteilt. Durch die Vereinigung dieser Venen entsteht die Vena poplitea. Diese geht in die Vena femoralis über. Durch Vereinigung mit der Vena profunda femoris wird die Vena femoralis communis gebildet, die oberhalb des Leistenbandes in die Vena iliaca externa übergeht. Diese wiederum vereinigt sich mit der Vena iliaca interna zur Vena iliaca communis, die mit der Vene der Gegenseite die Vena cava inferior bildet. Die Venen des Herz-Kreislauf-Systems haben zwei wesentliche Aufgaben, den Rücktransport des venösen Blutes zum Herzen und die Speicherung des Blutvolumens, das nicht sofort benötigt wird. Der Rücktransport des Blutes wird durch verschiedene Faktoren gewährleistet. Dazu zählen die Venenklappen, die thorakoabdominale Venenpumpe sowie die periphere Muskelpumpe. Die Speicherung des Blutes wird durch die Elastizität der Venenwand erreicht.

Patients undergoing major orthopedic surgery are at an increased risk of thromboembolism even after the acute postoperative phase. Therefore, prolonged thromboprophylaxis is currently recommended and widely used. The length of hospital stay after major orthopedic surgery is steadily decreasing and most patients are transferred to specialized rehabilitation centers in the early postoperative phase. Consequently, thromboprophylaxis is usually given during the rehabilitation period. Previously there have been no systematic studies of how many patients with asymptomatic thrombosis are transferred to a rehabilitation center or how many patients develop deep vein thrombosis (DVT) during rehabilitation. In the present study, 238 patients who had undergone major orthopedic surgery were examined by compression ultrasonography on day 1 or 2 and on day 20 of their rehabilitation phase in order to detect asymptomatic proximal DVT. Sonograms were read centrally with blinding to the clinical course of the patients. All patients received standard thromboprophylaxis during the acute postoperative phase. Prolonged thromboprophylaxis with enoxaparin was given during the rehabilitation phase. The mean duration of thromboprophylaxis was 36.8 days. At admission to the rehabilitation center, proximal DVT was identified in 16 patients (6.7%). New proximal DVT at discharge from the rehabilitation center was identified in 3.2% of patients following prolonged thromboprophylaxis with enoxaparin. In conclusion, a considerable percentage of patients with asymptomatic proximal DVT are transferred to rehabilitation centers following major orthopedic surgery. Using prolonged thromboprophylaxis, new proximal DVTs will still develop during rehabilitation, but at a low rate.

Making decisions about any modality of secondary prophylaxis in patients with venous thromobembolism (VTE) has to balance the risk of bleeding induced by anticoagulants against the benefit of reducing the risk of recurrent disease. It has to be kept in mind that the magnitude of risk is not only defined by the number of events per time period but also by the impact of the event on the fate of the patient. With standard intensity Vitamin K antagonists, the risk of bleeding is more closely related to comorbidities than to other factors, e.g. age. The risk of VTE recurrence differs largely between patient groups. The criterion of presence or absence of a permanent or transient clinical trigger factor for the actual VTE episode has a greater impact than an abnormal result in thrombophilia testing. The standard period of secondary prophylaxis for proximal deep vein thrombosis and for pulmonary embolism is three to six months. The concept of prolonging this period for several months according to the risk of recurrence is seriously challanged by the observation that the prolongation period seems to delay recurrencies rather than truly avoiding them. For this reason, patients who clearly are threatened by recurrent episodes should receive indefinitive secondary prophylaxis. This is the case for cancer patients, patients with the antiphospholipid syndrome, and those who belong to families with severe and symptomatic protein C, protein S, or antithrombin deficiencies. Patients with recurrent VTE, with idiopathic VTE, or with combined thrombophilic conditions may only benefit from indefinitive secondary prophylaxis if the bleeding risk of the anticoagulant regimen under consideration is very low.