The Clinical Significance of Hyponatremia Following Total Joint Arthroplasty

Introduction: Postoperative hyponatremia (sodium level <135 mEq/L) is common among total joint arthroplasty (TJA) patients. However, its impact on TJA outcomes remains unclear. Our study aimed to evaluate the relationship between postoperative hyponatremia and adverse outcomes following TJA. Methods: A retrospective review was conducted of patients undergoing inpatient primary and revision TJA between 2010 and 2023 at a large tertiary care center. Patients were segregated based on their preoperative and postoperative sodium (pre/post) status: normonatremic/normonatremic (Group 1; n = 3,441), normonatremic/hyponatremic (Group 2; n = 830), and hyponatremic/hyponatremic (Group 3; n = 110). Multivariate regression analyses controlling for age, sex, body mass index, Charlson Comorbidity Index score, operative time, and procedure type were performed to evaluate the risk of 90-day adverse medical and surgical outcomes. Results: Compared with Group 1, Group 2 had a significantly higher risk of any medical complication (odds ratio [OR]: 1.750, 95% confidence interval [CI]: 1.313-2.334; p < 0.001) as well as any other complication (OR: 1.629, 95% CI: 1.248-2.128; p < 0.001). This was largely driven by an increased risk of acute kidney injury (AKI; OR: 1.982; 95% CI: 1.451-2.709; p < 0.001), with no differences seen for the remaining complications. When excluding AKI, there were no differences in any evaluated complications between Group 1 and Group 2. There were no differences in rates of any surgical complications between evaluated groups (OR: 1.018; 95% CI: 0.552-1.877; p = 0.955). Mild postoperative hyponatremia was associated with a higher risk of AKI as well as medical and overall complications. Discussion: In the largest series to date, patients with postoperative hyponatremia largely had comparable 90-day outcomes to patients who were normonatremic postoperatively. These findings suggest that asymptomatic mild postoperative hyponatremia may unnecessarily increase resource utilization. These patients may be safely discharged without the additional costs associated with aggressive hyponatremia management. Level of Evidence: Level III. See Instructions for Authors for a complete description of levels of evidence.