In the present study, median age for joint replacement was 68 years, while the most common retirement age is 63 years (Finnish Centre for Pensions, ). In Finland, population structure is in a state of change. In the coming years, a large number of people will reach retirement age and also the typical age for joint replacement, while the economic dependency ratio is rising due to large number of people retiring and also due to the relatively smaller number of people of working age (Official Statistics
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joint replacement surgery had undiagnosed diabetes (Rajamäki et al., 2019). Thus, it could be assumed that the true prevalence of diabetes in this study population was around 25 to 30%. Yet this fact would presumably not introduce any bias into the results.
Fourth, the study used a unique, Scandinavian population and not all the results can necessarily be extrapolated to other types of populations with different racial and comorbid characteristics. Fifth, CKD equations make a distinction between black skinned and white populations. No information on ethnicity was collected and all patients were assumed to be white skinned, as indeed most of the population of Finland is. Sixth, given the retrospective nature of the study, showing relationships between different variables is possible, but causality cannot be established. Seventh, the present study was based on the eGFR calculation method that uses SCr as a covariate in the equations. It is known that this method is biased, because muscle mass affects SCr. More accurate methods exist, but their use has not gained wider clinical popularity. Hence, the study reflects the most common clinical practice, and is thus more readily interpretable in other clinics. Eight, the study sought to determine whether CKD stage was associated with implant survival, but in patients with CKD 4-5 there was a shortage of revision cases. Therefore, this study could not demonstrate any conclusion regarding these patients.
Ninth, a decidedly heterogenic variable, all-cause revision, was used as an endpoint in Study 4 as it is a clinically relevant and interesting question to ask. However, several types of revisions exist; those performed due to infections, fractures, or aseptic loosening, but also those due to relative indications such as recurrent dislocations, pain, and wear of the liner. Therefore, CKD stage, diabetes status and BMI all have different effects of each separate revision type. This induced complex unproportional hazards and therefore multivariable analysis was not feasible. In the study
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confounding factors were controlled for by stratification, which is probably the only reasonable way to answer the question. On the other hand, to be able to control for confounders using multivariable regression, it would be necessary to study all types of revisions separately. To do this, one would need a vast population, virtually a set of register data to ensure a propriate number of endpoints to have significant results.
Tenth, the literature on implant survival usually contains at least 10 years of follow up data (Jämsen et al., 2013; Mäkelä et al., 2014). In the present study, the follow-up time in implant survival is relatively short (median 5.6 years). However, 25% of the patients were followed up for over 8.1 years. Still, it is possible that the results would have been different in longer follow up. Finally, the present study did not ascertain whether renal function affects functional results and quality of life. Thus, the speculation of patient selection based on renal function is not conclusive.
Eleventh, revision data was collected from a single hospital. Therefore, not all revision operations were included. However, the revision database has been evaluated and it is known that it contains over 95% of all revisions performed among this population.
6.7 Conclusions and Future considerations
In the present study, median age for joint replacement was 68 years, while the most common retirement age is 63 years (Finnish Centre for Pensions, ). In Finland, population structure is in a state of change. In the coming years, a large number of people will reach retirement age and also the typical age for joint replacement, while the economic dependency ratio is rising due to large number of people retiring and also due to the relatively smaller number of people of working age (Official Statistics
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Finland ). As a conclusion, more joint replacement operations are going to be needed, while there may be a shortage of resources. Also, the number of CKD patients is increasing (Arffman et al., 2020). In this new situation it is increasingly important to direct resources to those patient groups which derive the greatest benefit.
It could be assumed that patients hope their joint replacement would last for the rest of their lives. The present study showed that patients with impaired renal function have limited life expectancy, but not compromised implant survival. In the long term, in patients with normal renal function, probability for death and any revision is substantially equal, whereas patients with CKD 3-5 have four to ten times greater probability for death than for any revision. This information is important for orthopedic surgeons but also for patients when considering the magnitude of the different risks preoperatively. In the present study, over 10% of patients undergoing joint replacement had CKD 3-5. Future studies are needed to address whether patients with advancing CKD stage and combined unfavorable morbidity profile also gain fewer quality adjusted life years. The cost effectiveness of joint replacement surgery in patients with compromised life expectancy would also be an interesting question, as it may be that improved mobility and pain relief could lengthen the time they could live in their own homes. From the patients´ perspective, all help in relieving pain and restoring function is welcome, even in patients with poor health and thus short life expectancy. Whether to prohibit their operative intervention due to shorter life expectancy, but not increased risk for revision operation, is most of all an ethical, but also an economic question that cannot be answered inclusively. Decisions should be made together with the patient after discussing the pros and cons of the operation.
Also,some political guidance may be necessary regarding the future allocation of resources.
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The present study showed that eGFR is a better predictor of mortality than SCr. It could be assumed that eGFR performs better in the prediction of other complications and adverse events as well. However, there are no studies to show this in joint
replacement populations. This warrants future research. Competing risk analysis showed that CKD is not associated with implant survival. Still, no association between CKD 4-5 and septic revisions could be demonstrated due to lack of patients. Thus, in the future this group needs to be studied in a different setting or with a larger
population. Also, repeating Study 4 would be extremely interesting after a median follow-up time of 15-20 years.
The present study had three novel findings. First, it reported a synergistic effect between CKD and diabetes in mortality during the first postoperative year, while the connection was reduced to additional effect at five years. Second, the study reported that duration of operation and ASA grade are both independent risk factors for AKI.
Third, the present study reported that CKD stage is the strongest predictor of mortality, even compared to CHF. As these three findings are novel and need verification in future studies.
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Finland ). As a conclusion, more joint replacement operations are going to be needed, while there may be a shortage of resources. Also, the number of CKD patients is increasing (Arffman et al., 2020). In this new situation it is increasingly important to direct resources to those patient groups which derive the greatest benefit.
It could be assumed that patients hope their joint replacement would last for the rest of their lives. The present study showed that patients with impaired renal function have limited life expectancy, but not compromised implant survival. In the long term, in patients with normal renal function, probability for death and any revision is substantially equal, whereas patients with CKD 3-5 have four to ten times greater probability for death than for any revision. This information is important for orthopedic surgeons but also for patients when considering the magnitude of the different risks preoperatively. In the present study, over 10% of patients undergoing joint replacement had CKD 3-5. Future studies are needed to address whether patients with advancing CKD stage and combined unfavorable morbidity profile also gain fewer quality adjusted life years. The cost effectiveness of joint replacement surgery in patients with compromised life expectancy would also be an interesting question, as it may be that improved mobility and pain relief could lengthen the time they could live in their own homes. From the patients´ perspective, all help in relieving pain and restoring function is welcome, even in patients with poor health and thus short life expectancy. Whether to prohibit their operative intervention due to shorter life expectancy, but not increased risk for revision operation, is most of all an ethical, but also an economic question that cannot be answered inclusively. Decisions should be made together with the patient after discussing the pros and cons of the operation.
Also,some political guidance may be necessary regarding the future allocation of resources.
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The present study showed that eGFR is a better predictor of mortality than SCr. It could be assumed that eGFR performs better in the prediction of other complications and adverse events as well. However, there are no studies to show this in joint
replacement populations. This warrants future research. Competing risk analysis showed that CKD is not associated with implant survival. Still, no association between CKD 4-5 and septic revisions could be demonstrated due to lack of patients. Thus, in the future this group needs to be studied in a different setting or with a larger
population. Also, repeating Study 4 would be extremely interesting after a median follow-up time of 15-20 years.
The present study had three novel findings. First, it reported a synergistic effect between CKD and diabetes in mortality during the first postoperative year, while the connection was reduced to additional effect at five years. Second, the study reported that duration of operation and ASA grade are both independent risk factors for AKI.
Third, the present study reported that CKD stage is the strongest predictor of mortality, even compared to CHF. As these three findings are novel and need verification in future studies.
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7. Conclusions
1) AKI is a rare complication of joint replacement operation having an incidence of 3.3/1000 operations. Factors associated with AKI were BMI, ASA
classification, duration of the operation and preoperative eGFR. AKI patients had poor survival compared to those who did not develop AKI.
2) Prevalence of CKD in joint replacement population varies between 9 and 13% depending on the method for estimating eGFR. CKD was most common among females, patients older than 75 years, knee replacement patients and patients with comorbid conditions. SCr should not be used for the evaluation of kidney function because it does not distinguish CKD at an acceptable rate. This was especially important in female patients older than 75 years, but also in patients older than 75 with normal weight.
3) Short- and long-term mortality increases remarkably in every stage up in CKD classification. CKD was the most powerful predictor of mortality when compared to other comorbid conditions. Patients with CKD 4-5 and patients with CKD 3-5 combined with diabetes, coronary disease or CHF had a high mortality rate postoperatively.
4) CKD stage is not associated with overall revision risk or the risk for revision for PJI. However, the study could not show if this also applies to patients with CKD 4-5.
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