The quality of evidence is downgraded by study limitations (lack of blinding), by inconsistency (variability in results), and by imprecise results (few outcome events and wide confidence intervals).
A Cochrane review [Abstract] 1 included 8 studies with a total of 3 818 adult subjects with no history of thromboembolic disease undergoing knee arthroscopy. Studies compared daily subcutaneous (sc) low-molecular-weight heparin (LMWH) versus control (5 studies); oral rivaroxaban 10 mg versus placebo (1 study); daily sc LMWH versus graduated compression stockings (GCS) (1 study); and aspirin versus control (1 study). The incidence of pulmonary embolism (PE) in all studies combined was low (7 cases in 3818 subjects), and there were no deaths in any of the intervention or control groups.
LMWH versus control (no intervention):There was no difference between LMWH and control in the incidence of PE (RR 1.81, 95% CI 0.49 to 6.65; 3 studies, n=1 820) or in the incidence of symptomatic deep vein thrombosis (DVT)(RR 0.61, 95% CI 0.18 to 2.03; 4 studies, n=1 848). LMWH reduced the risk of asymptomatic DVT (RR 0.14, 95% CI 0.03 to 0.61; 2 studies, n=369). There was no difference in the risk of all adverse events combined (RR 1.85, 95% CI 0.95 to 3.59; 5 studies, n=1 978), in major bleeding (RR 0.98, 95% CI 0.06 to 15.72; 1 study, n=1 451), or in minor bleeding (RR 1.79, 95% CI 0.84 to 3.84; 5 studies, n=1 978). LMWH versus GCS (1 study, n=1 317):There was no difference in the risk of PE (RR 1.00, 95% CI 0.14 to 7.05). LMWH reduced the risk of symptomatic DVT compared to GCS (RR 0.17, 95% CI 0.04 to 0.75). No difference was seen for asymptomatic DVT (RR 0.47, 95% CI 0.21 to 1.09), major bleeding (RR 3.01, 95% CI 0.61 to 14.88), or minor bleeding (RR 1.16, 95% CI 0.64 to 2.08).
Rivaroxaban 10 mg versus placebo (1 study, n=234): No PE events were observed in either group, and no difference in symptomatic DVT (RR 0.16, 95% CI 0.02 to 1.29), or asymptomatic DVT (RR 0.95, 95% CI 0.06 to 15.01) was detected. Only bleeding adverse events were reported. No major bleeds occurred in either group and there was no evidence of differences in minor bleeding between the groups (RR 0.63, 95% CI 0.18 to 2.19).
Aspirin versus control (1 study, n=170): No PE, DVT or asymptomatic events were detected in either group. No bleeds were reported.
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