Risk of venous thrombosis after arthroscopy of the knee: results from a large population‐based case–control study

Background From the currently available evidence, the risk of venous thrombosis after knee arthroscopy remains unclear. Objectives To estimate the risk of venous thrombosis after arthroscopy of the knee, and to identify high‐risk groups. Patients and Methods We used data from a large population‐based case–control study (the Multiple Environmental and Genetic Assessment of risk factors for venous thrombosis [MEGA] study) on the etiology of venous thrombosis (4416 cases; 6150 controls). Odds ratios (ORs) with 95% confidence intervals (CIs), adjusted for age, sex, body mass index, rheumatic disease, and regular exercise, were calculated. Results One hundred and three patients and 24 controls had a knee arthroscopy in the year before the index date, resulting in a six‐fold increased risk (OR 5.9, 95% CI 3.7–9.3). Ligament reconstructions led to a higher risk (OR 17.2, 95% CI 2.2–136) than meniscal surgery, diagnostic arthroscopy, or chondroplasty (OR 5.4, 95% CI 3.4–8.7). An additionally increased risk was found for combinations with genetic and acquired risk factors: with oral contraceptives (OR 46.6, 95% CI 6.1–353); and with factor V Leiden, factor II G20210A mutation, or non‐O blood type (OR 15.3, 95% CI 8.1–28.5). The risk of venous thrombosis was particularly high in the first 3 months after knee arthroscopy, with an 18‐fold increased risk (OR 16.2, 95% CI 7.8–33.7). Conclusions We observed a strongly increased risk of venous thrombosis after knee arthroscopy, especially in the first months after the procedure. The risk was particularly high in the presence of other acquired or genetic risk factors, making knee arthroscopy a high‐risk intervention in certain individuals.