Research published in The Journal of Bone and Joint Surgery found that patients with low sodium levels before or after total knee or hip surgery are more likely to have problems and other negative outcomes.

The journal is part of the Lippincott portfolio and is published in collaboration with Wolters Kluwer. Hyponatremia is an overlooked sign of trouble following total joint arthroplasty (TJA), according to the new research by Javad Parvizi, MD, FRCS, and colleagues of Rothman Orthopaedic Institute at Thomas Jefferson University.

They write, "Efforts should be made to evaluate and, if possible, address hyponatremia in the preoperative period." A large study looks at the incidence and impact of hyponatremia after TJA.

The researchers analysed 3,071 primary and revision TJAs performed at their high-volume orthopaedic surgery centre between 2015 and 2017.

All patients had at least one preoperative and one postoperative sodium measurement. The patient's average age was 67 years, and 54% were women. In 84.6% of patients, sodium levels were normal both preoperatively and postoperatively.

Another 9.4% of patients had normal sodium levels preoperatively but had hyponatremia (serum sodium level <135 milliequivalents per litre) postoperatively; 2.1% had hyponatremia preoperatively but normal sodium levels postoperatively; and 3.8% had hyponatremia both preoperatively and postoperatively.

Patients with postoperative hyponatremia were more likely to have a history of congestive heart failure, stroke, liver disease, and chronic kidney disease.

Postoperative hyponatremia was linked to increases in several adverse outcomes - particularly in patients who had low sodium levels both before and after TJA.

Patients in this group spent more time in the hospital (average 6.4 days), were more likely to be discharged to a rehabilitation or nursing centre rather than home (43%), and were more likely to be readmitted to the hospital within 90 days (18%).

A twofold increase in complications with postoperative hyponatremia

After adjustment for other factors, the risk of a complication was 2.1 times higher among patients who had hyponatremia postoperatively and 2.6 times higher among patients who had hyponatremia both preoperatively and postoperatively.

Patients with postoperative hyponatremia were also more likely to have a non-home discharge (1.7 and 3.0 times higher among those with normal and low preoperative sodium, respectively) and spent more days in the hospital after surgery.

Patients with greater decreases in sodium after TJA were at higher risk of each of these adverse outcomes. Hyponatremia was a significant risk factor for patients undergoing both primary and revision TJA.

For patients with preoperative hyponatremia that normalised after TJA, outcomes were similar to those of patients who had normal sodium levels both preoperatively and postoperatively.

Counterintuitively, patients with postoperative hyponatremia that were corrected after surgery but before hospital discharge had a longer length of stays, and worse outcomes than those who did not have their sodium corrected.

The study adds to previous evidence that hyponatremia is relatively common following TJA and can adversely affect the patients' postoperative course. "Patients who develop hyponatremia are likely to stay in the hospital longer and are more likely to experience complications and undergo non-home discharge," Dr Parvizi and coauthors write.

They suggest low serum sodium may be an indicator of poorer general health and low physiological reserve.

"Patients with preoperative and postoperative hyponatremia were particularly at risk," the researchers add. They emphasise the need for further studies to determine whether hydration protocols and other medical optimisation steps can mitigate the adverse effects of low sodium levels in patients undergoing TJA.