The study by Partridge and colleagues brings up to date a large body of literature demonstrating declining mortality rates following total hip replacement1. The authors analyzed 90-day inpatient mortality and 30-day adverse events following 540,623 total hip replacements performed in England and Wales from 2005 to 2014. They demonstrated a progressive decline in the mortality rate over time, from 0.60% to 0.15%, despite an increase in the levels of comorbidity among the patients. The decline in postoperative mortality was parallel to a fall in the rate of postoperative adverse events such as myocardial infarction, which fell from 0.5% to 0.2%, and pulmonary embolism (PE), which fell from 0.8% to 0.4%. In contrast, there was a rise in the rate of postoperative pneumonia (“lower respiratory tract infection”), from 0.5% to 0.8%, and renal failure, from 0.2% to 1.1%. Postoperative pneumonia and renal failure strongly increased the risk of death (odds ratios of 42 and 37, respectively).
It is important to note that during the study period, the National Health Service implemented a change in perioperative antibiotics, from cephalosporins to gentamicin plus a beta lactam penicillin, in order to reduce the rate of Clostridium difficile, which likely explains the spike in renal failure rates. A Scottish study also demonstrated a doubling of postoperative acute kidney injury in orthopaedic patients after this policy change2. This suggests that the increase in renal failure rates seen in this study should not be extrapolated to non-UK populations.
The relatively high rate of postoperative pneumonia in the current study is similar to that shown in a study of 168,848 Medicare patients undergoing total hip replacement from 2012 to 20143. In that study, 0.4% of patients experienced postoperative pneumonia, compared with only 0.2% experiencing myocardial infarction and 0.3% experiencing PE. Because of declining case-fatality rates, however, the higher rates of pneumonia have not translated into higher rates of death. For example, in the study by Partridge et al., only 0.03% and 0.02% of total hip replacements were followed by death from pneumonia and myocardial infarction, respectively, in 2014, as compared with 2005, when the rate was 0.1% for each of those complications.
Partridge et al. also examined risk factors for morbidity and mortality after total hip replacement with the goal of identifying at-risk groups in order to improve the accuracy of surgical consent. They demonstrate that, in 2014, patients with insulin-dependent diabetes had 6-times the odds of renal failure, 7-times the odds of myocardial infarction, and 4-times the odds of death from any cause. The odds of death were also higher (2 to 3-fold) in patients with ischemic heart disease, atrial fibrillation, and chronic obstructive pulmonary disease (COPD). The odds of pneumonia were 2.5-times higher in patients with atrial fibrillation and 3.5-times higher in patients with COPD, and the odds of renal failure more than doubled in patients with atrial fibrillation and non-insulin-dependent diabetes. Not surprisingly, the odds of myocardial infarction were 9-times higher in patients with ischemic heart disease. The authors did not assess other factors known to affect postoperative outcomes, such as hospital volume, type of anesthesia, smoking, body mass index, and social factors such as race, education, and socioeconomic status4.
Limitations of this study were that the authors only identified deaths that occurred in the hospital and counted total hip replacement cases rather than patients. This could have led to an underestimation of mortality rates since 10% of deaths occur outside the hospital1. In addition, since patients experiencing an adverse event may be less likely to have a second hip replacement (particularly if they die), low-risk patients were more likely to have had 2 procedures and been counted twice. This may have had the greatest impact on estimates of PE-related mortality (0.02% overall in this study), since PE occurs after hospital discharge in a third of cases5 and can be associated with sudden death.
In summary, this study suggests that we are making great headway in improving the safety of total hip replacement despite an ever-sicker patient population. Strategies to reduce the rate of postoperative pneumonia (now the most common complication after total hip replacement) such as immunization, smoking cessation, avoidance of general anesthesia, and incentive spirometry, should be encouraged in parallel with those aimed at cardiovascular and thrombotic risk reduction. In addition, tailored perioperative pathways should be developed that target patients at the highest risk of complications.
1. Lalmohamed A, Vestergaard P, de Boer A, Leufkens HG, van Staa TP, de Vries F. Changes in mortality patterns following total hip or knee arthroplasty over the past two decades: a nationwide cohort study. Arthritis Rheumatol. 2014 Feb;66(2):311-8.
2. Bell S, Davey P, Nathwani D, Marwick C, Vadiveloo T, Sneddon J, Patton A, Bennie M, Fleming S, Donnan PT. Risk of AKI with gentamicin as surgical prophylaxis. J Am Soc Nephrol. 2014 Nov;25(11):2625-32. Epub 2014 May 29.
3. Middleton A, Lin YL, Graham JE, Ottenbacher KJ. Outcomes over 90-day episodes of care in Medicare fee-for-service beneficiaries receiving joint arthroplasty. J Arthroplasty. 2017 Sep;32(9):2639-2647.e1. Epub 2017 Mar 30.
4. Soohoo NF, Farng E, Lieberman JR, Chambers L, Zingmond DS. Factors that predict short-term complication rates after total hip arthroplasty. Clin Orthop Relat Res. 2010 Sep;468(9):2363-71.
5. Bohl DD, Ondeck NT, Basques BA, Levine BR, Grauer JN. What is the timing of general health adverse events that occur after total joint arthroplasty? Clin Orthop Relat Res. 2017 Jan 4. [Epub ahead of print].