Barriers to the optimal use of anticoagulants after orthopaedic surgery.

Venous thromboembolism (VTE) and the consequent morbidity and mortality associated with this condition continue to be a problem following orthopaedic surgery. The vast majority of patients undergoing orthopaedic surgery receive some form of thromboprophylaxis. However, the use of inappropriate thromboprophylaxis is an important factor which may explain why the clinical burden of VTE is still considerable. Barriers to the use of appropriate thromboprophylaxis include the belief by some surgeons that pharmacological thromboprophylaxis increases the risk of bleeding and the asymptomatic nature of deep vein thrombosis. In addition, in patients at risk of VTE, thromboprophylaxis should be given beyond the standard duration recommended in international or national guidelines, and many surgeons have concerns about adherence and adverse events in the outpatient setting. Furthermore, currently available anticoagulants have drawbacks, including the need for monitoring, or a subcutaneous route of administration. The introduction and implementation of multi-faceted and integrated approaches to thromboprophylaxis could improve adherence with current guidelines, extend appropriate thromboprophylaxis according to risk factors, and improve patient outcomes in this setting. In addition, the development of new anticoagulants with more convenient administration regimens and no need for monitoring may help to achieve these objectives.

Major joint replacement. A model for antithrombotic drug development: from proof-of-concept to clinical use.

AIM: Development of antithrombotic compounds has traditionally been performed in patients undergoing total hip and knee replacement surgery. A high number of asymptomatic deep-vein thromboses are radiologically detectable, and bleeding and other adverse events (AE) are easy to observe. However, standardization of study procedures and endpoints in early proof-of-concept studies and late pure clinical endpoint studies has been lacking. This has made comparison between studies difficult, economic analyses speculative and potential benefits of applying the drug regimen in non-selected patients uncertain. In this paper, the International Surgical Thrombosis Forum proposes a strategy for the clinical investigation of new pharmacological agents for the prophylaxis of postoperative thrombotic events. METHODS: First, dose titration safety studies of short duration, in highly selected patients using objective venographic endpoints are recommended. Bleeding should be divided into the quantified volume of surgical bleeding and other adjudicated clinical bleeding events. The number of AE should be described for each dose step and classified according to International Coding of Diagnoses (ICD). Second, a dose confirmatory study of moderate exposure period and sufficient follow-up time is recommended. The exclusion criteria should be restricted to contraindications of the compared drugs and technical procedure. RESULTS: The efficacy, bleeding and AE should be similar to those used in dose-titration studies. In addition, the failure rate of the drug to exert its effect and the net clinical benefit should be calculated. CONCLUSION: Finally, trials with simple clinical endpoints and long follow-up should be conducted to evaluate the potential benefits of the drug-regimen in non-selected populations.

Comparison of real-time B-mode ultrasonography and bilateral ascending phlebography for detection of postoperative deep vein thrombosis following elective hip surgery. The Venous Thrombosis Group.

A prospective study compared real-time B-mode ultrasound examination with bilateral ascending phlebography in the diagnosis of postoperative deep vein thrombosis in 60 patients undergoing elective total hip replacement. The overall sensitivity and specificity of the ultrasound method were 54 and 91%, respectively, and the positive and negative predictive values were 83 and 69%, respectively. The rather low overall sensitivity of the ultrasound method in this study was due to difficulty in detecting thrombi smaller than 1 cm wherever they were located in the deep veins, and in diagnosing thrombi in the calf, regardless of their size. We conclude that real-time B-mode ultrasonography is a technique that can easily be used routinely for detection of postoperative DVT in hip surgery, but its sensitivity for proximal thrombosis (63%) is too low for it to be used alone.

Thromboprophylaxis with low molecular weight heparin after major orthopaedic surgery is cost effective.

The objective of this analysis was to evaluate the socioeconomic consequences of routine administration of low molecular weight heparin (LMWH) as thromboprophylaxis in patients undergoing total hip arthroplasty, on the basis of data from a number of clinical studies. Despite the higher direct costs associated with LMWH, this regimen was more cost effective per thromboembolic complication prevented than no prophylaxis, dextran 70, or low dose unfractionated heparin. A sensitivity analysis was performed to address the outcome when the main factors in the economic analysis were changed; this had no significant effect on the conclusions of the study.

A comparative review of the adverse effect profiles of heparins and heparinoids.

On the basis of the results of the 11 studies reviewed, thromboprophylaxis with unfractionated heparin, low molecular weight (LMW) heparin or a heparinoid (danaparoid sodium; Org 10172) in patients undergoing total hip replacement did not show any important clinical differences with respect to the tolerability profiles of the different compounds. However, as a result of the great variability in the presentation and evaluation of blood losses and bleeding complications in these studies, it is mandatory to perform a direct comparison of the different compounds in question in a double-blind, prospective clinical study.

Accuracy of magnetic resonance imaging in the diagnosis of deep vein thrombosis in asymptomatic patients with injuries of the lower extremity. A pilot study.

This is a prospective comparative study of magnetic resonance imaging (MRI) of the deep veins versus contrast venography in consecutive patients treated for various injuries to their lower extremities, showing no clinical symptoms of deep vein thrombosis. The majority of examinations referred to in this study were performed according to the following methodology: First, the patient was subjected to MRI. Subsequently, within a 24-h interval, he/she was subjected to contrast venography. The acquired results were compared in a blinded manner. The diagnostic indices for MRI were calculated on the assumption that the results of contrast venography were sure to give an accurate indication of either presence or absence of thrombosis. Thirty-six patients were included in the study, of which 27 (15 males) completed it. The overall incidence of distal deep venous thrombosis (DVT) was 22% (6/27). One patient showed extension of a crural thrombus into the popliteal vein. MRI did not detect any of the thrombi. This lack of result was ascribed to failure to fully demonstrate all segments of the crural veins. However, MRI did show three proximal thrombi in the superficial femoral vein, which were not shown by the venograms. Thus, both the sensitivity and specificity of MRI were 0%, so MRI proved to be of no value in the diagnosis of asymptomatic deep venous thrombosis in this study.

Poor correlation between soluble fibrin concentrations measured by two commercially available immunoassays.

Soluble fibrin (SF) has attracted considerable interest as a marker for haemostatic activation. Two new enzyme immunoassays for SF, Enzymun-Test FM (Boehringer Mannheim, Germany) and Fibrinostika Soluble Fibrin (Organon Teknika, Belgium) have recently become commercially available. We measured plasma levels of SF in clinically obtained blood samples in order to compare the two new assays. Blood was drawn from 10 healthy volunteers and from 149 patients on the first day after surgery for fractures of the upper part of the femur. Collection and processing was done according to the manufacturers' recommendations. In the patients, levels found by the two assays were significantly different. The Enzymun-Test assay reported a median (range) of 11.87 (2.66 - > 62.20) mg/l, whereas the Fibrinostika assay found a median (range) of 3.34 (1.08 - >10) mg/l. The correlation coefficient was 0.38 (Spearman). A poor correlation was thus found between values obtained by the two assays in the patient category chosen. Further validation of the assays is necessary.

Components of coagulation and fibrinolysis during thrombosis prophylaxis with a low molecular weight heparin (Enoxaparin) versus Dextran 70 in hip arthroplasty.

In a prospective randomized study heptest, thrombin-antithrombin complexes (TAT), D-dimer, and t-PA:ag were analysed pre- and postoperatively in 206 consecutive patients undergoing hip arthroplasty during thromboprophylaxis with either a LMW heparin (Enoxaparin) or Dextran 70. Deep vein thrombosis (DVT) developed in 6 of 102 (6%) Enoxaparin and in 21 of 104 (20%) Dextran patients diagnosed by bilateral phelobography. In the Enoxaparin group heptest showed a significant increase from the pre- to the postoperative level opposed to a significant decrease in the Dextran group. Postoperative levels of TAT, D-dimer, and t-PA:ag were significantly increased in both groups, however, TAT was significantly higher in patients in the Dextran group than in the Enoxaparin patients. D-dimer was significantly higher in Dextran patients with DVT postoperatively compared with patients without DVT. No differences concerning TAT or t-PA:ag were observed between patients with and without DVT in any of the groups.

Association between plasma levels of tissue plasminogen activator and postoperative deep vein thrombosis--influence of prophylaxis with a low molecular weight heparin. The Venous Thrombosis Group.

In a prospective, randomized controlled study, tissue plasminogen activator (t-PA) and tissue plasminogen activator antigen (t-PA:ag) were measured pre- and postoperatively in 40 consecutive patients undergoing total hip replacement. Patients received either a subcutaneous injection of low molecular weight heparin or placebo once daily. Deep vein thrombosis was diagnosed by bilateral phlebography. Patients who developed postoperative thromboembolic complications had significantly lower preoperative t-PA activity levels than patients who did not develop such complications. No difference was observed between the two groups with respect to t-PA:ag. Thromboprophylaxis with low molecular weight heparin did not cause any significant changes in t-PA activity and t-PA:ag. This study in high risk patients indicates that impaired fibrinolysis may be associated with development of thromboembolic complications after operation.

Markers of coagulation and fibrinolysis after fractures of the lower extremities.

The study was performed to detect activation of coagulation and fibrinolysis in terms of prothrombin fragment 1 and 2 (F1 + 2), thrombin-antithrombin III complex (TAT), fibrin degradation products (FbDP), fibrinogen degradation products (FgDP), and soluble fibrin monomers (FM) in plasma from 39 patients with fractures of the lower extremities. We found substantially elevated levels of the molecular markers at admission and on the day after admission (Day 1) compared with control levels. Admission levels of F1 + 2, TAT, FbDP and FgDP were significantly higher compared with levels on day 1, whereas levels of FM were not significantly different between the two days. Generally there were good correlations between all markers of coagulation and fibrinolysis at admission whereas correlations were weaker or absent on day 1. In conclusion we found substantial haemostatic activation as a immediate response to trauma. Increased levels of F1 + 2, TAT, FM, FbDP and FgDP appear to be a normal physiological reaction after fractures of the lower extremities.

Efficacy and safety of prolonged thromboprophylaxis with a low molecular weight heparin (dalteparin) after total hip arthroplasty--the Danish Prolonged Prophylaxis (DaPP) Study.

The aim of this study was to compare the efficacy and safety of prolonged (35 days) thromboprophylaxis with a standard length (7 days) regimen of a low molecular weight heparin in patients undergoing total hip arthroplasty. The study was multicentre, randomised, double-blind, and prospective with two groups. Following seven days on a standard length regimen of dalteparin (5000 antifactor Xa units subcutaneously once daily starting 12 h before surgery), patients were randomized to continue the prophylaxis with either subcutaneous injections of dalteparin or placebo injections for a further 28 days. Efficacy was evaluated at the end of the study (day 35) in all patients with bilateral ascending phlebography to detect deep vein thrombosis. Bleeding complications and other adverse events were registered throughout the study period. Three hundred consecutive patients agreed to participate before the operation: 281 were finally randomised and 215 completed the study; two patients died before randomisation; 17 developed deep vein thrombosis; none developed pulmonary embolism; and five of 113 patients (4.4%, 95% CI 1-10%) developed deep vein thrombosis in the dalteparin group, compared with 12 of 102 (11.8%; 95% CI 6-20%) in the placebo group (p=0.039). Deep vein thrombosis in the proximal veins was diagnosed in one patient (0.9%; 95% CI 0-5%) in the dalteparin group, and in five (5.0%; 95% CI 2-11%) in the placebo group (p=0.076). Major bleeding was observed in one patient in the placebo group; minor bleeding complications and adverse events were equally distributed between the groups. We concluded that prolonged (35 days) thrombo prophylaxis with dalteparin is more effective than a standard length (7 days) regimen without increased risk of bleeding complications or other adverse events.

Clinical limitations of risk assessment models.

Appropriate thromboprophylaxis in hospital patients is effective in preventing clinically important venous thromboembolic events, including deep vein thrombosis (DVT) and fatal pulmonary embolism. Due to the risk of bleeding associated with pharmacological prophylaxis and the cost of administering prophylactic drugs, the clinical benefit and cost-effectiveness of thromboprophylaxis may be optimized by providing prophylaxis only to patients at risk of thrombosis, and tailoring the intensity of prophylaxis to the level of risk. Accurate assessment of patients' thromboembolic risk is therefore highly necessary. Thromboembolic risk is influenced by numerous factors. Several risk factor indices based on clinical risk factors and laboratory variables have been proposed since the 1970s, but these have not been widely adopted due to their complexity and lack of prospective validation. The method of deriving risk data on which these indices are based is questioned, and older prognostic indices excluded recently identified risk factors, particularly molecular factors such as the clotting factor V Leiden mutation, further undermining their clinical value. A number of much simpler risk assessment models (RAMs) have now been developed which stratify patients into low-, moderate- and high-risk categories. However, no RAM currently available provides comprehensive guidance for all patient groups. Use of poorly designed RAMs may fail to identify some patients at risk, leading to omission of prophylaxis and preventable thrombotic events. Certain patient groups develop DVT despite prophylaxis. Current RAMs are not validated to identify these patients. Well-designed and well-validated RAMs, incorporated into standard practice guidelines in hospitals, should contribute to improved clinical outcomes and economic benefits of prophylaxis.

Reduction of plasma levels of prothrombin fragments 1 and 2 during thromboprophylaxis with a low-molecular-weight heparin.

In a randomized double-blind placebo-controlled study, plasma levels of prothrombin fragment 1 and 2 and total fibrin/fibrinogen degradation products were measured preoperatively and on days 1, 3, 5 and 7 postoperatively in 131 patients undergoing total hip replacement. Patients received a subcutaneous injection of either a low molecular weight heparin (Logiparin) or placebo once daily. Postoperative deep vein thrombosis was diagnosed by bilateral phlebography 7 to 10 days after operation. In the placebo group postoperative levels of prothrombin fragments 1 and 2 and total fibrin/fibrinogen degradation products were significantly higher in patients with postoperative thromboembolic complications, whereas in the low-molecular-weight heparin group no statistical differences were observed. Compared with placebo the administration of a low-molecular-weight heparin was associated with a significant reduction in the levels of prothrombin fragments 1 and 2 and total degradation products. Our observations suggest that the postoperative thrombin generation is moderated by thromboprophylaxis with Logiparin.

Levels of thrombin--antithrombin-III complex and factor VIII activity in relation to post-operative deep vein thrombosis and influence of prophylaxis with a low-molecular-weight heparin.

In a randomized doubled-blind placebo-controlled study, plasma levels of thrombin-antithrombin-III (TAT) and factor VIII activity (VIII:C) were measured pre-operatively and on days 1, 3, 5 and 7 post-operatively in 70 consecutive patients undergoing total hip replacement. Patients received either a subcutaneous injection of low-molecular-weight heparin (LMWH) or placebo once daily. Post-operative deep vein thrombosis (DVT) was diagnosed by bilateral phlebography. The levels of TAT and VIII:C both increased significantly after operation and were not significantly influenced by LMWH. Thirty-three patients in whom post-operative DVT developed had a significantly lower level of VIII:C on day 7, compared with patients without DVT.

Perioperative thrombosis prophylaxis with low molecular weight heparins in elective hip surgery. Clinical and economic considerations.

A review and meta analysis of randomized prophylaxis studies in total hip arthroplasty (THA) surgery with the low molecular weight heparin (LMWH) compounds presently marketed in Europe. Thromboprophylaxis with recommended dosages of LMWH was significantly more effective than both placebo (no prophylaxis), dextran 70 and low-dose unfractionated heparin (UH) (5,000 IU thrice daily) in terms of protection against objectively diagnosed deep vein thrombosis (DVT), which is the main source of postoperative pulmonary embolism. The efficacy of LMWH was similar to that of adjusted-dose UH but only 2 studies have been conducted with this regimen so far. When combined with 0.5 mg dihydroergotamine (DHE), UH was as effective as LMWH, but DHE bears a definite risk of circulatory disturbances in the lower limbs. In all studies LMWH prophylaxis was safe under the clinical conditions. A cost-effectiveness analysis based on the reported efficacy and safety of LMWH in the European studies showed that, compared with no prophylaxis, dextran 70, and low-dose UH, LMWH prophylaxis used routinely in patients undergoing THA is more profitable for the health care system due to fewer expenses used on treatment of postoperative thromboembolic complications. LMWH therefore leads to better utilization of the economic resources.

Dose relation in the prevention of proximal vein thrombosis with a low molecular weight heparin (tinzaparin) in elective hip arthroplasty.

This is a review of a double-blind, prospective study comparing the thromboprophylactic efficacy and safety of two different prophylactic regimens of a low molecular weight heparin (tinzaparin) in 250 consecutive patients (aged < or 18) undergoing primary elective hip arthroplasty. Regimen 1: 75 U anti-Xa/kg BW (actual range 63 to 91) once daily started 12 hours before operation; and regimen 2: 50 U anti-Xa/kg BW (actual range 41 to 71) once daily started 2 hours before operation. Both regimens were administered in a weight-adjusted fashion and were continued for 7 days after operation or until full mobilization. Efficacy was evaluated by occurrence of postoperative deep vein thrombosis (DVT) diagnosed by bilateral ascending phlebography on day 7 +/- 2 after operation, and the venograms were evaluated in an assessor blind fashion by a panel of three expert radiologists. Safety was evaluated by the amount of blood lost and transfusion requirements during and after the operation; all bleeding complications, reoperations, adverse events and deaths were observed during the study. A 3-month follow-up on survival and occurrence of thromboembolism was performed on all randomized patients. The result was a significantly better protective effect against proximal DVT by regimen 1 compared with regimen 2. This was achieved with improved safety in terms of a significantly decreased need for blood transfusions during operation and fewer wound complications in the postoperative period in favor of regimen 1. Therefore, tinzaparin administered in a dosage of 75 U anti-Xa/kg BW 12 hours before surgery is significantly more protective against proximal DVT and safer than the standard regimen of 50 U anti-Xa/kg BW started 2 hours before surgery in patients undergoing primary elective hip arthroplasty.

Managing the risk of thrombosis in the perioperative period in patients undergoing orthopedic and trauma surgery with low-molecular-weight heparin: enoxaparin.

Patients undergoing arthroplastic surgery of the lower limbs and those with multiple injuries have a high risk of thromboembolism. Enoxaparin is a highly effective antithrombotic drug that is well tolerated and without the need for monitoring. Numerous controlled trials in these patient groups have demonstrated enoxaparin to be at least as effective as heparin in reducing the occurrence of deep vein thrombosis while showing a tendency towards lower risk of bleeding complications; therefore, enoxaparin is recommended as thromboprophylaxis in patients undergoing major hip or knee surgery or suffering from multiple trauma.

Managing the risk of thrombosis in the perioperative period in patients undergoing orthopedic and trauma surgery with low-molecular-weight heparin: enoxaparin.

ABSTRACTPatients undergoing arthroplastic surgery of the lower limbs and those with multiple injuries have a high risk of thromboembolism. Enoxaparin is a highly effective antithrombotic drug that is well tolerated and without the need for monitoring. Numerous controlled trials in these patient groups have demonstrated enoxaparin to be at least as effective as heparin in reducing the occurrence of deep vein thrombosis while showing a tendency towards lower risk of bleeding complications; therefore, enoxaparin is recommended as thromboprophylaxis in patients undergoing major hip or knee surgery or suffering from multiple trauma.

[Low-molecular weight heparin. A new agent to prevent thrombosis]. / Lavmolekylaert heparin. Et nyt tromboseprofylaktikum.

The theory for employment of low molecular weight heparin and the material concerning employment of low molecular weight heparin hitherto published is reviewed. To date, it has been demonstrated that low molecular weight heparin has the same antithrombotic efficacy as unfractionated heparin and its half life is approximately twice as long. This implies that adequate thrombosis prophylaxis can be obtained with a single daily dose.

[Low molecular heparin in prevention of thrombosis in orthopedic surgery]. / Tromboseprofylakse med lavmolekylaert heparin i ortopaedkirurgien.

The review encompasses all published clinical studies of prophylactic treatment with low molecular weight (LMW) heparins marketed in Denmark when used to prevent thrombosis in patients undergoing elective or emergency orthopaedic operations. In elective hip surgery, LMW-heparin was more effective than placebo in reducing the incidence of deep vein thrombosis. There was significantly better anti-thrombotic effect of LMW-heparin, given in recommended doses, than of Dextran 70. When compared to low-dose heparin, the incidence of deep vein thrombosis was lowest using LMW-heparin, but only one study found the difference significant. LMW-heparin compared to low-dose heparin in combination with dihydroergotamine showed no significant difference with respect to either effect of safety. The use of LMW-heparin as prophylactic treatment for patients with either trochanteric or femoral neck fractures is as yet not nearly so well-documented. The relatively few studies that have been carried out show large variation between the different LMW-heparins. There is need for a study comparing the effect of LMW-heparin with that of low-dose heparin in these patients, both with respect to thrombosis prevention and influence on total mortality.