Low-molecular-weight heparin followed by rivaroxaban or not for the prevention of deep venous thromboembolism after total knee arthroplasty

Direct factor Xa inhibitors versus low molecular weight heparins or vitamin K antagonists for prevention of venous thromboembolism in elective primary hip or knee replacement or hip fracture repair

BACKGROUND

People undergoing major orthopaedic surgery are at increased risk of postoperative thromboembolic events. Low molecular weight heparins (LMWHs) are recommended for thromboprophylaxis in this population. New oral anticoagulants, including direct factor Xa inhibitors, are recommended as alternatives. They may have more advantages than disadvantages compared to LMWHs and vitamin K antagonists (VKAs, another type of anticoagulant).

OBJECTIVES

To assess the benefits and harms of prophylactic anticoagulation with direct factor Xa inhibitors compared with low molecular weight heparins and vitamin K antagonists in people undergoing major orthopaedic surgery for elective total hip or knee replacement or hip fracture surgery.

SEARCH METHODS

We searched the Cochrane Vascular Specialised Register, CENTRAL, MEDLINE, Embase, two other databases, and two trial registers to 11 November 2023. We conducted reference checks to identify additional studies.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) comparing the effects of direct factor Xa inhibitors to LMWHs or VKAs in people undergoing major orthopaedic surgery.

DATA COLLECTION AND ANALYSIS

We used standard Cochrane methods. Our primary outcomes were all-cause mortality, major venous thromboembolism (VTE), symptomatic VTE, major bleeding, and serious hepatic and non-hepatic adverse events. We evaluated the risk of bias in the included studies using Cochrane's risk of bias 1 tool. We calculated estimates of treatment effects using risk ratios (RR) with 95% confidence intervals (CIs), and used GRADE criteria to assess the certainty of the evidence.

MAIN RESULTS

We included 53 RCTs (44,371 participants). Participants' average age was 64 years (range: 18 to 93 years). Only one RCT compared a VKA with direct factor Xa inhibitors. All 53 RCTs compared direct factor Xa inhibitors with LMWHs. Twenty-three studies included participants undergoing total hip replacement; 21 studies, total knee replacement; and three studies included people having hip fracture surgery. The studies' average duration was approximately 42 days (range: two to 720 days). Compared to LMWHs, direct factor Xa inhibitors may have little to no effect on all-cause mortality, but the evidence is very uncertain (RR 0.83, 95% CI 0.52 to 1.31; I2 = 0%; 28 studies, 29,698 participants; very low-certainty evidence). Direct factor Xa inhibitors may make little to no difference to major venous thromboembolic events compared to LMWHs, but the evidence is very uncertain (RR 0.51, 95% CI 0.37 to 0.71; absolute risk difference: 12 fewer major VTE events per 1000 participants, 95% CI 16 fewer to 7 fewer; I2 = 48%; 28 studies, 24,574 participants; very low-certainty evidence). Compared to LMWHs, direct factor Xa inhibitors may reduce symptomatic VTE (RR 0.64, 95% CI 0.50 to 0.83; I2 = 0%; 33 studies, 31,670 participants; low-certainty evidence). The absolute benefit of substituting factor Xa inhibitors for LMWHs may be between two and five fewer symptomatic VTE episodes per 1000 patients. In the meta-analysis with all studies pooled, direct factor Xa inhibitors appeared to make little or no difference to major bleeding compared to LMWHs, but the evidence was very uncertain (RR 1.05, 95% CI 0.86 to 1.30; I2 = 15%; 36 studies, 39,778 participants; very low certainty-evidence). • In a subgroup analysis limited to studies comparing rivaroxaban to LMWHs, people given rivaroxaban may have had more major bleeding events (RR 1.94, 95% CI 1.26 to 2.98; I2 = 0%; 17 studies, 17,630 participants; low-certainty evidence). The absolute risk of substituting rivaroxaban for LMWH may be between one and seven more major bleeding events per 1000 patients. • In a subgroup analysis limited to studies comparing direct factor Xa inhibitors other than rivaroxaban to LMWHs, people given these other direct factor Xa inhibitors may have had fewer major bleeding events, but the evidence was very uncertain (RR 0.80, 95% CI 0.63 to 1.02; absolute risk difference: 3 fewer major bleeding events per 1000 participants, 95% CI 5 fewer to 0 fewer; I2 = 0%; 19 studies, 22,148 participants; very low-certainty evidence). Direct factor Xa inhibitors may make little to no difference in serious hepatic adverse events compared to LMWHs, but the evidence is very uncertain (RR 3.01, 95% CI 0.12 to 73.93; 2 studies, 3169 participants; very low-certainty evidence). Only two studies reported this outcome, with one death in the intervention group due to hepatitis reported in one study, and no events reported in the other study. People given direct factor Xa inhibitors may have a lower risk of serious non-hepatic adverse events than those given LMWHs (RR 0.89, 95% CI 0.81 to 0.97; I2 = 18%; 15 studies, 26,246 participants; low-certainty evidence). The absolute benefit of substituting factor Xa inhibitors for LMWH may be between three and 14 fewer serious non-hepatic adverse events per 1000 patients. Only one study compared a direct factor Xa inhibitor with a VKA. It reported outcome data with imprecise results due to the small number of events. It showed no difference in the effects of the study drugs.

AUTHORS' CONCLUSIONS

Oral direct factor Xa inhibitors may have little to no effect on all-cause mortality, but the evidence is very uncertain. Oral direct factor Xa inhibitors may slightly reduce symptomatic VTE events when compared with LMWH. They may make little or no difference to major VTE events, but the evidence is very uncertain. In the evaluation of major bleeding, the evidence suggests rivaroxaban results in a slight increase in major bleeding events compared to LMWHs. The remaining oral direct factor Xa inhibitors may have little to no effect on major bleeding, but the evidence is very uncertain. Oral direct factor Xa inhibitors may reduce serious non-hepatic adverse events slightly compared to LMWHs. They may have little to no effect on serious hepatic adverse events, but the evidence is very uncertain. Due to the high rates of missing participants and selective outcome reporting, the effect estimates may be biased.

Utility of D-dimer in total joint arthroplasty

As the number of patients receiving total joint replacements continues to rise, considerable attention has been directed towards the early detection and prevention of postoperative complications. While D-dimer has long been studied as a diagnostic tool in venous thromboembolism (VTE), this assay has recently received considerable attention in the diagnosis of periprosthetic joint infection (PJI). D-dimer values are substantially elevated in the acute postoperative period after total joint arthroplasty, with levels often exceeding the standard institutional cutoff for VTE (500 µg/L). The utility of D-dimer in detecting VTE after total joint replacement is currently limited, and more research to assess its value in the setting of contemporary prophylaxis protocols is warranted. Recent literature supports D-dimer as a good to excellent biomarker for the diagnosis of chronic PJI, especially when using serum sample technique. Providers should exercise caution when interpreting D-dimer levels in patients with inflammatory and hypercoagulability disorders, as the diagnostic value is decreased. The updated 2018 Musculoskeletal Infection Society criteria, which includes D-dimer levels > 860 µg/L as a minor criterion, may be the most accurate for diagnosing chronic PJI to date. Larger prospective trials with transparent lab testing protocols are needed to establish best assay practices and optimal cutoff values for D-dimer in the diagnosis of PJI. This review summarizes the most current literature on the value of D-dimer in total joint arthroplasty and elucidates areas for future progress.

Permeation-Enhancing Nanoparticle Formulation to Enable Oral Absorption of Enoxaparin

This study tests the hypothesis that association complexes formed between enoxaparin and cetyltrimethylammonium bromide (CTAB) augment permeation across the gastrointestinal mucosa due to improved encapsulation of this hydrophilic macromolecule within biocompatible poly (lactide-co-glycolide, PLGA RG 503) nanoparticles. When compared with free enoxaparin, association with CTAB increased drug encapsulation efficiency within PLGA nanoparticles from 40.3 ± 3.4 to 99.1 ± 1.0%. Drug release from enoxaparin/CTAB PLGA nanoparticles was assessed in HBSS, pH 7.4 and FASSIFV2, pH 6.5, suggesting effective protection of PLGA-encapsulated enoxaparin from unfavorable intestinal conditions. The stability of the enoxaparin/CTAB ion pair complex was pH-dependent, resulting in more rapid dissociation under simulated plasma conditions (i.e., pH 7.4) than in the presence of a mild acidic gastrointestinal environment (i.e., pH 6.5). The intestinal flux of enoxaparin complexes across in vitro Caco-2 cell monolayers was greater when encapsulated within PLGA nanoparticles. Limited changes in transepithelial transport of PLGA-encapsulated enoxaparin complexes in the presence of increasing CTAB concentrations suggest a significant contribution of size-dependent passive diffusion as the predominant transport mechanism facilitating intestinal absorption. Graphical abstract.

Venous thromboembolism prophylaxis strategies for people undergoing elective total knee replacement: a systematic review and network meta-analysis

BACKGROUND

Hospital-associated venous thromboembolism is a major patient safety concern. Provision of prophylaxis to patients admitted for elective total knee replacement surgery has been proposed as an effective strategy to reduce the incidence of venous thromboembolism. We aimed to assess the relative efficacy and safety of all available prophylaxis strategies in this setting.

METHODS

We did a systematic review and Bayesian network meta-analyses of randomised controlled trials to assess the relative efficacy and safety of venous thromboembolism prophylaxis strategies and to populate an economic model that assessed the cost-effectiveness of these strategies and informed the updated National Institute for Health and Care Excellence (NICE) guideline recommendations for patients undergoing elective total knee replacement surgery. The Cochrane Library (CENTRAL), Embase, and Medline were last searched on June 19, 2017, with key terms relating to the population (venous thromboembolism and total knee replacement) and the interventions compared, including available pharmacological and mechanical interventions. Outcomes of interest were deep vein thrombosis (symptomatic and asymptomatic), pulmonary embolism, and major bleeding. Risk of bias was assessed, and relevant data extracted from the included randomised controlled trials for the network meta-analyses. Relative risks (RR; with 95% credible intervals [95% CrI]) compared to no prophylaxis, median ranks (with 95% CrI), and the probability of being the best intervention were calculated. The study was done in accordance with PRISMA guidelines.

FINDINGS

25 randomised controlled trials were included in the network meta-analyses. 23 trials (19 interventions; n=15 028) were included in the deep vein thrombosis network, 12 in the pulmonary embolism network (13 interventions; n=15 555), and 19 in the major bleeding network (11 interventions; n=19 797). Risk of bias ranged from very low to high. Rivaroxaban ranked first for prevention of deep vein thrombosis (RR 0·12 [95% CrI 0·06-0·22]). Low molecular weight heparin (LMWH; standard prophylactic dose, 28-35 days) ranked first in the pulmonary embolism network (RR 0·02 [95% CrI 0·00-3·86]) and LMWH (low prophylactic dose, 10-14 days) ranked first in the major bleeding network (odds ratio 0·08 [95% CrI 0·00-1·76]), but the results for pulmonary embolism and major bleeding are highly uncertain.

INTERPRETATION

Single prophylaxis strategies are more effective in prevention of deep vein thrombosis in the elective total knee replacement population than combination strategies, with rivaroxaban being the most effective. The results of the pulmonary embolism and major bleeding meta-analyses are uncertain and no clear conclusion can be made other than what is biologically plausible (eg, that no prophylaxis and mechanical prophylaxis strategies should have the lowest risk of major bleeding).

FUNDING

National Institute for Health and Care Excellence.