Background: Postoperative thromboses are among the most feared complications in orthopedic surgery, possibly causing life-threatening conditions in otherwise highly successful procedures such as total joint replacement. Body weight is an important risk factor for thromboses and is being used in algorithms to determine dosages in prophylaxis. However, weight patterns among orthopedic populations have changed considerably since the introduction of these algorithms, essentially shifting towards obesity. This study asks whether present-day obese patients are essential under-dosed and would benefit from higher than usual dosages of bemiparin sodium in the prophylaxis of postoperative thrombosis.

Patients and Methods: To ensure sufficient power a sample of 750 patients, allocated into two cohorts receiving either 3,500 IU or 5,00o IU bemiparin sodium were followed postoperatively for 6 weeks and blindly assessed for clinically symptomatic thrombotic events. Differences in rates of thrombotic events were modeled using mulitvariate Poisson regression including potential confounders severity of immobilisation, gender, exact weight, and age as covariates. A p-value of 5% was considered significant.

Results: Information on 723 patients for a total of 66.8 person-years was analysed per intention-to-treat. The adjusted incidence rate ratio was 0.35 (95%CI: 0.03 to 2.91). Thus there was not evidence for a difference in rates between groups. There was, however, a borderline significant association between rates and body weight, suggesting a potential benefit of higher dosages in even heavier patients. There were no complications due to higher dosages of bemiparin sodium.

Conclusion: We did not see a significant reduction of incidence rates of thromboses with higher dosages of bemiparin in this population. However, there was some evidence that higher dosages might prove beneficial as populations further gain weight.