People with osteoarthritis who go on to have a total or partial knee replacement do not appear to have an increased risk of all-cause mortality, but the jury is still out on whether they gain any improvement, a study showed.
In their research published in the Annals of the Rheumatic Diseases [2016 May 17. doi: 10.1136/annrheumdis-2016-209167], Dr. Devyani Misra of Boston University and colleagues noted that knee replacement (KR) was thought to decrease long-term mortality risk because of the relief from pain and improvement in function that typically comes with surgery. However, studies on the topic had been conflicting, largely because of the challenges associated with studying mortality with KR surgery in observational settings.
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In the current study the research team sought to evaluate the relation of KR to the risk of all-cause mortality among subjects with knee OA, while at the same time giving particular attention to “potential sources of confounding bias that may account for [the] effect of KR on mortality.”
Using patient data from the U.K. primary care electronic database THIN, the investigators compared the risk of mortality among 14,042 subjects who had OA, were aged 50-89 years old, and had had or had not had KR.
They discovered a strong protective effect of KR on all-cause long-term mortality risk, particularly among the adults over 63 years of age.
For example, people who had undergone KR had a 28% lower risk of mortality than did non-KR subjects (hazard ratio, 0.72; 95% confidence interval, 0.66-0.78).
In the overall propensity score–matched study sample, crude mortality per 1,000 person-years (total person-years) for the KR and non-KR cohorts were 19 (61,015) and 25 (58,294), respectively.
However, despite their best efforts, the researchers said the results showed evidence of residual confounding.
“For example, the observation of improved survival immediately after KR, despite the expectation of potential short-term increased postoperative mortality risk supports the presence of residual confounding,” they wrote.
Another finding suggestive of confounding was that the protective effect was seen only in older patients (over 63) when the authors stratified study participants by age.
“While it is possible that survival benefit seen in older patients with KR is a true effect because it is in this group that greater physical activity is particularly important to survival, more likely it is a result of residual confounding because subject selection is rigorous in this age group due to vulnerability,” the authors wrote.
They concluded that knee replacement “did not appear to be associated with an increased risk of all-cause mortality.”
“While we cannot rule out that KR may potentially reduce the risk of mortality over the long term, the true extent of that potential benefit is difficult to discern due to confounding by indication in observational studies using administrative data or electronic health records,” they added.
This study was funded by the Arthritis Foundation Postdoctoral Fellowship Award, the ACR Rheumatology Research Foundation Investigator Award, and a Boston University scholarship grant.