Hyponatraemia After Hip and Knee Replacement: Incidence, Risk Factors, Clinical Consequences and Management in the...

Introduction: Total hip replacements and total knee replacements are among the most frequently performed operations worldwide, and the demand for such procedures is ever-growing. It is essential to focus on preventable medical complications that can arise from these procedures, specifically postoperative hyponatraemia. Postoperative hyponatraemia has an incidence of 20-40% in total hip and knee replacement patient cohorts. Even mild postoperative hyponatraemia is clinically relevant, as it is associated with cognitive impairment and gait disturbance and may undermine the aims of enhanced recovery protocols. Severe postoperative hyponatraemia can lead to seizures, coma, intensive care admission, and death. Although uncommon, the high volume of patients treated in busy orthopaedic centres means such cases will inevitably be encountered. This narrative review summarises the current evidence on incidence, risk factors and consequences of postoperative hyponatraemia in total hip and knee replacement populations. Methods: A literature review was performed through the EBSCO and PubMed databases to identify relevant studies. Key search terms included were "hyponatraemia", "total hip replacement", and "total knee replacement". Results: The incidence of postoperative hyponatraemia is largely between 20% and 40%; however, there are some outliers to this. Multiple risk factors have been identified through observational studies, including age, preoperative hyponatraemia, female sex and certain medications, which signal a need for a risk stratification strategy that can assist in preoperative assessment and the early identification of patients at higher risk of developing postoperative hyponatraemia. Evidence is scarce regarding interventional studies for the prevention and management of postoperative hyponatraemia, despite multiple studies highlighting the issue. Conclusion: Future work should focus on testable, quality improvement interventions, such as automatic sodium checks on postoperative day one, weight-based oral fluid protocols, oral salt supplementation, and escalation pathways for high-risk patients. Incorporating these into enhanced recovery frameworks has the potential not only to optimise safe early discharge for the majority but also to prevent rare but significant complications.