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Reference - N Engl J Med 2016 Dec 3 early online (level 2 [mid-level] evidence)
- Prophylactic LMWH may reduce the risk of symptomatic VTE after many procedures, but its efficacy following knee arthroscopy or lower leg casting in patients without history of VTE is unclear.
- Two recent trials each randomized over 1,500 adults without history of VTE to prophylactic LMWH (either dalteparin or nadroparin) vs. no anticoagulant therapy following knee arthroscopy or lower leg casting, respectively.
- In both trials, incidence of symptomatic VTE within 3 months post-procedure was low, and prophylactic LMWH did not significantly alter the risk of symptomatic VTE or major or clinically relevant bleeding.
Prophylactic LMWH may reduce the risk of developing symptomatic VTE following many surgical procedures, but its efficacy after knee arthroscopy or after lower leg casting is unclear (Chest 2012 Feb;141(2 Suppl):e195S, Chest 2012 Feb;141(2 Suppl):e278S). Systematic reviews suggest some benefit with LMWH, but these have focused on non-symptomatic VTE (alone or as part of a composite outcome) or have included some trials that did not exclude patients with history of VTE (Arthroscopy 2014 Mar;30(3):406, Arthroscopy 2014 Aug;30(8):987, Cochrane Database Syst Rev 2014 Apr 25;(4):CD006681). To further assess LMWH in preventing symptomatic VTE following knee arthroscopy or lower leg casting in patients without a history of VTE, two similar trials were conducted in which patients were randomized to prophylactic LMWH (either dalteparin or nadroparin) subcutaneous injection vs. no anticoagulant therapy. The POT-KAST trial included 1,543 adults (mean age 49 years) having knee arthroscopic procedures, with the LMWH group having injections once daily for 8 days post-surgery. The POT-CAST trial included 1,519 adults (mean age 46 years) having lower leg casting for ≥ 1 week, with the LMWH group having injections once daily during the period of leg immobilization. Patients were excluded for a history of VTE, pregnancy, anticoagulant use (but antiplatelet use allowed), or contraindications to LMWH. All patients were provided with information regarding signs and symptoms of VTE and were followed for 3 months post-procedure. Any suspicion of symptomatic VTE was confirmed with imaging.
In patients who had knee arthroscopy, symptomatic VTE occurred in 0.7% (95% CI 0.2%-1.6%) with LMWH and 0.4% (95% CI 0.1%-1.2%) without anticoagulants (not significant). In patients who had lower leg casting, symptomatic VTE occurred in 1.4% (95% CI 0.7%-2.5%) vs. 1.8% (95% CI 1%-3.1%) (not significant). There were also no significant differences between groups in frequencies of major bleeding or non-major clinically relevant bleeding in either of the two trials. Similar results were reported in per-protocol analyses excluding patients who did not adhere to the treatment regimen.
The POT-KAST and POT-CAST trials did not find a significant reduction in risk of developing symptomatic VTE with prophylactic LMWH following knee arthroscopy or lower leg casting in patients without history of VTE. A significant limitation of this trial is a lack of placebo control, as patients knowing they did not have prophylaxis may be more vigilant in reporting any symptoms. Also, the confidence intervals in both trials cannot exclude the possibility of a small reduction in risk of symptomatic VTE, particularly with patients with lower leg casting. It should be emphasized that the results of these trials do not extend to patients with history of VTE or are otherwise at increased risk of VTE. Nevertheless, unless indicated otherwise, the results of these trials argue against routine prophylactic LMWH after knee arthroscopy or lower-leg casting.
For more information, see the DynaMed Plus topics Venous thromboembolism (VTE) prophylaxis for orthopedic surgery patients and Venous thromboembolism (VTE) prophylaxis for medical patients. DynaMed users click here.