Routine administration of thromboprophylaxis is the standard of care for patients undergoing major orthopedic surgery due to the very high rate of postoperative venous thromboembolism (VTE). However, because prophylaxis is not 100% effective, a significant proportion of patients who receive thromboprophylaxis develop post-operative VTE (“breakthrough VTE”). Clinical and surgical characteristics that are associated with the development of VTE in orthopedic surgery patients who receive standard thromboprophylaxis have not been well characterized.


To evaluate the incidence of and risk factors for breakthrough VTE in patients who underwent major orthopedic surgery at a tertiary care hospital in Montreal, Canada.


Charts from consecutive patients who underwent total hip arthroplasty (THA), total knee arthroplasty (TKA) or hip fracture surgery (HFS) (hip pinning or hemiarthroplasty) from August 1, 1999 to April 30, 2000 were abstracted using standardized case report forms. Data were collected on patient characteristics (including VTE risk factors and postoperative complications), surgical characteristics (including type of surgery, operative factors, type of anesthetic) and thromboprophylaxis regimen. The results of any tests performed for clinically suspected VTE were documented, and associations between potential risk factors and objectively confirmed VTE were examined.


Over the 9 month study period, 310 patients underwent major orthopedic surgery (34% THA, 30% TKA, and 36% HFS) and received standard thromboprophylaxis with either dalteparin or enoxaparin (mean duration of prophylaxis: 7 days). Of 83 suspected VTE, 44 (7 proximal DVTs and 37 distal DVTs; 14% of study population; median onset 6 days post-op) were confirmed with objective testing (compression ultrasonography). Multivariate analyses showed that knee surgery (odds ratio [OR] 4.8, 95% confidence interval 2.3, 10.1) and type of low molecular weight heparin (enoxaparin: protective) (OR 0.39, 95% confidence interval 0.20, 0.80) independently predicted VTE. Patient characteristics such as previous VTE, malignancy, hormonal therapy or varicose veins were not associated with VTE.

Conclusion Despite receiving standard thromboprophylaxis, 14% of patients undergoing major orthopedic surgery developed symptomatic breakthrough VTE. Factors that independently predicted VTE in our population were TKR surgery and type of low molecular weight heparin. Our results suggest that TKR patients may warrant more aggressive post-operative physiotherapy and ambulation and adjunctive prophylactic measures such as pneumatic compression. In addition, due to the heterogeneity of different low molecular weight heparin compounds, direct comparison of the effectiveness of enoxaparin with dalteparin for orthopedic prophylaxis in prospective, randomized trials seems warranted.

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