Patient History and Risk
Patients undergoing elective hip or knee arthroplasty are already at high risk for venous thromboembolism. The practitioner might further assess the risk of venous thromboembolism by determining whether these patients had a previous venous thromboembolism.

Rationale
Patients undergoing elective hip or knee arthroplasty are at high risk for venous thromboembolic disease (VTED). Only one risk factor, previous history of VTED, has sufficient evidence indicating that some of these patients may be at even higher risk.

The relevant evidence comes from two studies that evaluated patients with a personal history of VTED – one of medium and one of low strength. The Pedersen study of over 68,000 patients found a relative risk of 8.1, and the Warwick study of over 14,000 patients found a hazard ratio of 4.92 for post-operative VTED in patients with a previous history of VTED (see Table 20 for a summary of the results of these studies).

Twenty-nine studies addressed whether patients with one or more potential risk factors, other than previous VTED, have higher rates of VTED. The list of potential VTED risk factors for which we sought evidence is listed in Table 19. The studies were all of low or very low quality (see Table 49 in Appendix XIII for a summary of our appraisal of the quality and applicability of these studies). A statistically significant increase in VTED resulting from these other risk factors that confer an increased risk of VTED in surgeries other than primary hip or knee arthroplasty was not found in studies of hip or knee arthroplasty patients. This might be because these other VTED risk factors confer a lower overall risk than primary hip or knee arthroplasty surgery itself. Therefore, their effects may not be seen against the relatively high background risk already being experienced by patients receiving elective hip or knee arthroplasty. Therefore, we are unable to recommend further risk stratification based on these factors.

No data specific to hip or knee arthroplasty were found addressing many potential risk factors, and in many instances where it was found, it was of very low quality and it was contradictory (see Table 19 for a summary of the results of these studies and Table 21 for a detailed presentation of their results). Data from patients undergoing surgical procedures other than primary hip and knee arthroplasty were found also of very low quality (Table 23) and therefore were unreliable. We excluded some of the studies we retrieved to address this recommendation. These studies, and the reasons for their exclusion are listed in Appendix XIV, Table 58.

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