Timing of acute myocardial infarction in patients undergoing total hip or knee replacement: a nationwide cohort study.

BACKGROUND Limited evidence suggests that the risk of acute myocardial infarction (AMI) may be increased shortly after total hip replacement (THR) and total knee replacement (TKR) surgery. However, risk of AMI in these patients has not been compared against matched controls who have not undergone surgery. The objective of this study was to evaluate the timing of AMI in patients undergoing THR or TKR surgery compared with matched controls. METHODS Retrospective, nationwide cohort study within the Danish national registries. All patients who underwent a primary THR or TKR (n = 95,227) surgery from January 1, 1998, through December 31, 2007, were selected and matched to 3 controls (no THR or TKR) by age, sex, and geographic region. All study participants were followed up for AMI, and disease- and medication history-adjusted hazard ratios (HRs) were calculated. RESULTS During the first 2 postoperative weeks, the risk of AMI was substantially increased in THR patients compared with controls (adjusted HR, 25.5; 95% CI, 17.1-37.9). The risk remained elevated for 2 to 6 weeks after surgery (adjusted HR, 5.05; 95% CI, 3.58-7.13) and then decreased to baseline levels. For TKR patients, AMI risk was also increased during the first 2 weeks (adjusted HR, 30.9; 95% CI, 11.1-85.5) but did not differ from controls after the first 2 weeks. The absolute 6-week risk of AMI was 0.51% in THR patients and 0.21% in TKR patients. CONCLUSIONS Risk of AMI is substantially increased in the first 2 weeks after THR (25-fold) and TKR (31-fold) surgery compared with controls. Risk assessment of AMI should be considered during the first 6 weeks after THR surgery and during the first 2 weeks after TKR surgery.