5. Results
5.3 Renal function among patients undergoing hip or knee joint replacement
5.3.1 Prevalence of CKD (Study 2)
The overall prevalence of CKD was 9% (n = 1,698), 13% (n = 2,178), and 12% (n = 2,139) according to the MDRD, CG, and CKD-EPI formulae respectively, whereas 10% of the study population had elevated SCr. The median preoperative eGFR using MDRD, CG, and CKD-EPI formulae were 87 (interquartile range [IQR] 73-101), 92 (IQR 72-116), and 85 mL/min/1.73m2 (IQR 72-94) respectively. Median SCr was 70 µmol/L (IQR 61-81).
5.3.1.1 Prevalence of CKD in different patient groups (Study 2)
Prevalence was highest among female patients older than 75 years with comorbidities who were undergoing knee replacement. CKD patients had lower preoperative hemoglobin, higher ASA classification and poorer preoperative function. Prevalence did not differ between primary and revision joint replacement patients. BMI had no linear association with CKD but CKD prevalence was highest when BMI was between 30 and 35kg/m2. (Table 15)
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5.2.3 Retrospectively analyzed contributing factors for AKI (Study 1)
Most of the AKI patients had multiple
contributing factors for AKI (Table 14). In half of the AKI cases, duration of operation
exceeded two hours. Postoperative AKI occurred predominantly in those with pre-existing eGFR less than 90mL/min/1.73m2.
5.2.4 Potential causes of AKI (Study 1)
Potential cause of AKI was identified retrospectively in 28 cases; 15 patients had infection, five patients had cardiac morbidities and five patients had pseudo-obstruction postoperatively. In 28 of the AKI cases, no underlying cause could be identified retrospectively. Two patients lacked the patient files and thus the underlying cause could not be reviewed.
Table 14. Factors possibly contributing in development of AKI in 58 patients
Risk factor Frequency (missing)
ASA class ≥ 3 Lowest BP ≤ 80 mmHg1
Blood transfusion
47 (2) 14 (4) 14 (5)
BMI ≥ 30 26 (12)
Duration ≥ 120 min 30 (2) eGFR≤ 90 ml/min 49 Medication combination2 10 (9)
Perioperative NSAID´s 20 (9) Preop anemia3
Use of vasoactives4
22 (4) 11
1Perioperative lowest measured systolic blood pressure
2Concomitant use of three or more of the following drugs perioperative period: diuretics, angiotensin converting enzyme inhibitors (ACEis) or angiotensin receptor blockers (ARBs), NSAIDs
3Anemia was defined as hemoglobin <117 g/l in women and <134 g/l in men.
4Atropin or Etilefrin
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5.2.5 Assessment of loss- and end-stage kidney disease among 58 AKI patients (Study 1)
Two patients needed dialysis treatment postoperatively but for under three weeks and thus were not classified to have either loss- or end-stage kidney disease.
5.3 Renal function among patients undergoing hip or knee joint replacement
5.3.1 Prevalence of CKD (Study 2)
The overall prevalence of CKD was 9% (n = 1,698), 13% (n = 2,178), and 12% (n = 2,139) according to the MDRD, CG, and CKD-EPI formulae respectively, whereas 10% of the study population had elevated SCr. The median preoperative eGFR using MDRD, CG, and CKD-EPI formulae were 87 (interquartile range [IQR] 73-101), 92 (IQR 72-116), and 85 mL/min/1.73m2 (IQR 72-94) respectively. Median SCr was 70 µmol/L (IQR 61-81).
5.3.1.1 Prevalence of CKD in different patient groups (Study 2)
Prevalence was highest among female patients older than 75 years with comorbidities who were undergoing knee replacement. CKD patients had lower preoperative hemoglobin, higher ASA classification and poorer preoperative function. Prevalence did not differ between primary and revision joint replacement patients. BMI had no linear association with CKD but CKD prevalence was highest when BMI was between 30 and 35kg/m2. (Table 15)
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Table 15. Patient demographics and prevalence of preoperative CKD in different demographic groups calculated with CKD-EPI formula
Descriptor All patients non-CKD patients CKD patients p
All patients 18,575 16,436 [88.5%] 2,139 [11.5%]
[missing, n=1,719] [median, IQR] 28.6 28.6 [25.5-32.0] 28.7 [25.8-32.3] 0.172
Body Mass Index
Harris Hip Score [missing, n=3167]
[median, IQR] 53 53 [41-64] 46 [35-56] <0.001
Knee Society Score [missing, n=3678]
[median, IQR] 47 47 [36-58] 45 [34-57] 0.009
Preoperative hemoglobin (g/dL) [median, IQR]
[missing, n=72] 13.8 13.9 [13.0-14.8] 13.1 [12.2-14.0] <0.001
Diagnosis [missing, n=34]
Numbers represent number of patients unless otherwise stated IQR refers to interquartile range
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The differences in CKD prevalence between patients undergoing TKA were analyzed.
Knee replacement patients were more obese (29.4 vs 27.4; P < 0.001), and had more diabetes (9% vs. 7%, P < 0.001) and hypertension (31% vs. 24%, P < .001) when compared to hip replacement patients. Because of these differences, a multivariable logistic regression analysis was performed using joint, diabetes, hypertension and BMI as covariates and CKD as an outcome. Regardless of these adjustments, hip
replacement patients had significantly lower probability of having preoperative CKD (OR 0.79, 95% CI 0.72-0.86).
5.3.2 Prevalence of different CKD stages (Studies 1, 3, and 4)
In Studies 1 and 3, normal kidney function (CKD stage 1) was present preoperatively in 6,519 (35.1%) of the patients, while 9,917 (53.4%), 2,023 (10.9%), 81 (0.4%) and 35 (0.2%) had CKD stages 2, 3, 4, and 5 respectively according to the CKD-EPI formula.
In Study 4, the proportions of different CKD stages were similar.
5.3.3 Value of serum creatinine (Study 2)
Using solely SCr as a measurement of kidney function, two to seven percent of CKD cases are missed depending on the equation used. However, the great majority of missed cases were female patients. Also, patients of normal weight and older age were at great risk of being classified as having normal kidney function using only SCr.
(Table 16) Also, in Study 3, CKD stage predicted long-term mortality better than SCr
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Table 15. Patient demographics and prevalence of preoperative CKD in different demographic groups calculated with CKD-EPI formula
Descriptor All patients non-CKD patients CKD patients p
All patients 18,575 16,436 [88.5%] 2,139 [11.5%]
[missing, n=1,719] [median, IQR] 28.6 28.6 [25.5-32.0] 28.7 [25.8-32.3] 0.172
Body Mass Index
Harris Hip Score [missing, n=3167]
[median, IQR] 53 53 [41-64] 46 [35-56] <0.001
Knee Society Score [missing, n=3678]
[median, IQR] 47 47 [36-58] 45 [34-57] 0.009
Preoperative hemoglobin (g/dL) [median, IQR]
[missing, n=72] 13.8 13.9 [13.0-14.8] 13.1 [12.2-14.0] <0.001
Diagnosis [missing, n=34]
Numbers represent number of patients unless otherwise stated IQR refers to interquartile range
63 5.3.1.2 Further analyses (Study 2)
The differences in CKD prevalence between patients undergoing TKA were analyzed.
Knee replacement patients were more obese (29.4 vs 27.4; P < 0.001), and had more diabetes (9% vs. 7%, P < 0.001) and hypertension (31% vs. 24%, P < .001) when compared to hip replacement patients. Because of these differences, a multivariable logistic regression analysis was performed using joint, diabetes, hypertension and BMI as covariates and CKD as an outcome. Regardless of these adjustments, hip
replacement patients had significantly lower probability of having preoperative CKD (OR 0.79, 95% CI 0.72-0.86).
5.3.2 Prevalence of different CKD stages (Studies 1, 3, and 4)
In Studies 1 and 3, normal kidney function (CKD stage 1) was present preoperatively in 6,519 (35.1%) of the patients, while 9,917 (53.4%), 2,023 (10.9%), 81 (0.4%) and 35 (0.2%) had CKD stages 2, 3, 4, and 5 respectively according to the CKD-EPI formula.
In Study 4, the proportions of different CKD stages were similar.
5.3.3 Value of serum creatinine (Study 2)
Using solely SCr as a measurement of kidney function, two to seven percent of CKD cases are missed depending on the equation used. However, the great majority of missed cases were female patients. Also, patients of normal weight and older age were at great risk of being classified as having normal kidney function using only SCr.
(Table 16) Also, in Study 3, CKD stage predicted long-term mortality better than SCr
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(Table 17).SCr recognized CKD with a sensitivity of 72% (1,531 out of 2,139 patients) and specificity of 98% (16,140 out of 16,436 patients).
Table 16. Prevalence of CKD [eGFR < 60mL/min], according to different formulae, among 16,748 patients with normal SCr levels
Older age and BMI < 25kg/m2
≥ 75 203 [14.7%] 775 [56.1%] 274 [19.8%]
Primary osteoarthritis 279 [2.0%] 985 [7.8%] 528 [3.8%]
Secondary osteoarthritis 10 [1.1%] 33 [4.0%] 19 [2.1%]
Rheumatoid arthritis 6 [1.1%] 54 [10.0%] 8 [1.4%]
MDRD = Modification of Diet in Renal Disease, CG = Cockcroft-Gault, CKD-EPI = Chronic Kidney Disease Epidemiology Collaboration
1Anemia was defined as hemoglobin <117 g/l in women and <134 g/l in men.
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Table 17. Survival of patients depending on their renal function Survival, %
†Adjusted by for BMI, congestive heart failure, coronary disease, diabetes, and hypertension; *adjusted for BMI, congestive heart failure, coronary disease, diabetes, and hypertension; CKD = chronic kidney disease; HR = hazard ratio;
CKD-EPI = Chronic Kidney Disease Epidemiology Collaboration; eGFR = estimated glomerular filtration rate.