Recent studies showed that the prevalence rates of CKD in TKA patients are between 6 % and 27 % [16, 17]. In this study, we found the CKD patients carried higher risks of postoperative mortality and re-admission, compared to the non-CKD patients. The CKD patients had a higher probability of postoperative transfusion than their non-CKD counterparts. However, the CKD did not affect the risks of postoperative infection, revision or LOS.
Ponnusamy et al.  found the CKD affected bone volume, mineralization, linear growth, and strength . Tan et al.  demonstrated the patients with end-stage CKD carried a higher risk of VTE, because the increased inflammatory state produces the hypercoagulability . The chronic inflammation produces excessive fluid in the soft tissue surrounding the knee and increases the risks of periprosthetic infection and revision surgery . The CKD is often associated with a poor nutritional status, electrolyte disorders, decreased immunity, and anemia [1, 8, 21, 22]. Those factors also increase the risk of postoperative infection. McCleery et al.  reported that the CKD increased the risk of early periprosthetic infection by 50 %.
However, there are different conclusions. Chen et al.  retrospectively evaluated 15 CKD patients (18 knees) who underwent TKA with antibiotic-loaded cement, and no infection was reported after a mean follow-up period of 25 months. Ling et al.  evaluated 13 CKD patients (18 knees) who underwent TKA, and no infection was found after a mean follow-up period of 5 years. Warth et al.  found that there were no differences between the CKD patients and non-CKD patients regarding the infectious surgical site complications, such as superficial or deep wound infection, organ space infection or wound dehiscence. Several studies revealed the combined use of antibiotic-loaded bone cement and systemic antibiotic therapy can decrease the risk of postoperative infection, but similar infection rates were reported in both CKD and non-CKD patients . Wang et al.  did not find an increased infection rate even in the patients who experienced a long period of dialysis vintage.
McCleery et al.  found the patients on dialysis had an increased revision rate within one year after TKA, but the result is similar to the revision rate of non-CKD patients. However, Miric et al.  found there was no difference between the early and later revision rates. The most common cause of revision TKA is the periprosthetic joint infection, accounted for 62 % of all revision TKAs . We found the similar revision rates in the CKD and the non-CKD patients. However, confirming the actual causes of revision is often difficult, which affects the assessment of the actual revision rates.
Patients with CKD and on long-term dialysis are often associated with renal anemia, metabolic imbalance, elevated risk of bleeding, and poor vascular circulation . Graves et al.  showed that the degree of anaemia was more pronounced in patients with more advanced CKD. Moreover, the intra- and postoperative blood loss ranges from 800 mL to 1000 mL . Kaiser et al.  found the CKD patients had a higher rate of transfusion (24 %) compared to non-CKD patients (8 %). Our study also supports this conclusion.
Death is a rare and devastating complication of TKA, but the early reported mortality rates range from 17 to 58 % in CKD patients [6, 30, 31]. Ponnusamy et al.  reported athe mortality rate of 1 % in dialysis-dependent patients. Several articles reported that the CKD is the independent risk factor of mortality in the early 90 days, and is the independent risk factor of morbidity in the early 30 days [13, 32, 33]. Warth et al.  demonstrated the incremental mortality was associated with an increased risk of postoperative pulmonary and cardiovascular complications. Our meta-analysis supports these findings.
Our sensitivity analysis was conducted among the outcomes with a high heterogeneity. Removing any single study did not change the statistical results. Therefore, we believe our findings in this meta-analysis are reliable.
Our meta-analysis has limitations. First, the retrospective studies included may lead to potential biases. Second, analyzing all CKD patients together without considering the severity may cause sampling bias, because there is a dose-dependent relationship between the severity of CKD and outcomes of TKA . Third, owing to the relatively short duration of follow-up, infection and revision rates were potentially underestimated. Fourth, the presence of publication bias is likely to decrease our confidence in the meta-analytic findings . Fifth, each comorbidity (diabetes, heart failure, peripheral vascular disease, hypertension, etc.) is analysed as an independent risk factor, but overlooking the fact that the patients with multimorbidities may lead to selection bias . Sixth, in the future, more high quality and matched control studies should be conducted to improve the statistical efficiency and precision.