Risk of acute myocardial infarction in patients with total hip/knee replacements and matched controls: A population-based cohort study in Denmark

Introduction: Although evidence is conflicting, risk of acute myocardial infarction (AMI) may be increased after total hip and knee replacement (THR/TKR). However, risk of AMI in these patients has not been compared against control subjects. The objective of this study was to estimate hazard ratios (HR) for AMI in THR/TKR patients versus matched controls. Methods: We carried out a nationwide cohort study in Denmark (1998-2007). Patients with a primary THR/TKR (n=95,227) were matched to three controls by age, sex, and region. All subjects were followed for AMI, and time-dependent Cox models were used to derive disease history and drug use adjusted (adj.) HRs. Results: Among THR patients versus controls, risk of AMI was substantially increased in the first two weeks post surgery (adj. HR 9.20; 95% CI 7.97- 10.60). The risk remained elevated within 2-6 weeks postoperatively (adj. HR 2.30; 95% CI 1.89-2.81), and then dropped to baseline levels. For TKR patients, AMI risk was only increased during the first two weeks (adj. HR 5.72; 95% CI 4.21-7.79), and was similar to their matched controls two weeks after surgery. Among THR patients, the six-week AMI risk was seven-fold increased among patients aged ≥80 years. The risk of AMI was 40-fold increased among patients with a previous AMI and 9-fold increased among patients with cerebrovascular disease. Conclusion: This is probably the first study that shows that THR (9-fold) and TKR patients (6-fold) are at increased risk of AMI during the first two weeks after surgery. These findings support evidence for risk assessment of AMI during the first six weeks after THR, and during the first two weeks after TKR.