The role of low molecular weight heparin in total knee arthroplasty.

Low-molecular-weight heparin prophylaxis is an acceptable, if not superior, alternative to heparin and warfarin prophylaxis in TKA. Considering the current popularity of pharmacologic prophylaxis after total hip and total knee arthroplasty and the advantages of low-molecular-weight heparins over traditional pharmacologic agents, these agents have the potential to become the prophylactic agent of choice against DVT in TKA. There are several practical differences between low molecular weight heparins and warfarin. Low molecular weight heparins are administered by subcutaneous injection and do not require drug-level or blood monitoring. Warfarin, although administered orally, must be maintained within an appropriate international normalized ratio (INR=2-3) with daily dose adjustments and takes 36 hours to produce a measurable effect, which may leave patients relatively unprotected during the early postoperative period. Comparative trials have demonstrated that low molecular weight heparins are more efficacious than warfarin in producing a greater overall reduction in the incidence and risk of DVT, but show similar rates of PE. Some studies suggest that bleeding may be a greater problem with low molecular weight heparin. Despite the superior efficacy of low molecular weight heparin, the prevalence of venous thromboembolism after TKA continues to be substantial compared with total hip arthroplasty, with at least a quarter of patients still affected. Additional prophylaxis strategies for this indication are needed and could include combining mechanical prophylaxis (eg, external pneumatic compression) with low molecular weight heparin. An appropriate management strategy should be established for all patients undergoing TKA. This should include identification of high-risk patients, cautious transfusion of blood products, pharmacologic prophylaxis with an acceptable agent for TKA, early mobilization, postoperative screening in high-risk patients, and continuing pharmacologic prophylaxis for an appropriate period postoperatively.