Low sodium levels linked to poor results after total joint replacement, finds study

The Journal of Bone and Joint Surgery, part of the Lippincott portfolio and published in collaboration with Wolters Kluwer, found that patients with low sodium levels before or after total knee or hip surgery are more likely to have complications and adverse effects.

Dr.Javad Parvizi, MD, FRCS, and colleagues at the Rothman Orthopaedic Institute at Thomas Jefferson University emphasize hyponatremia, a common electrolyte abnormality caused by an excess of total body water when compared to total body sodium content (a serum sodium concentration of less than approximately 135 mEq/L) that is commonly overlooked as a sign of trouble following total joint arthroplasty (TJA). They write, "Efforts should be made to evaluate and, if possible, address hyponatremia in the pre-operative period."

A large-scale study points at the incidence and impact of hyponatremia after TJA.

The researchers analyzed 3,071 primary and revision TJAs performed at their high-volume orthopedic surgery center between 2015 and 2017. The average age of patients was 67 years, and 54% were women.

All patients had at least one preoperative and one postoperative sodium measurement. 

Both preoperative and postoperative sodium levels were within acceptable limits in 84.6% of individuals. 3.8% of patients had hyponatremia both preoperatively and postoperatively, 2.1% had hyponatremia preoperatively but normal sodium levels postoperatively; and 9.4% of patients had normal sodium levels preoperatively but hyponatremia (serum sodium level of 135 milliequivalents per liter) postoperatively. A history of congestive heart failure, stroke, liver illness, or chronic kidney disease was more prevalent in patients with postoperative hyponatremia.

Particularly in patients who had low sodium levels both before and after TJA, postoperative hyponatremia was associated with elevations in a number of negative outcomes.

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 center rather than home (43%), and were more likely to be readmitted to the hospital within 90 days (18%).

Twofold increase in complications with postoperative hyponatremia

After controlling other factors, patients with postoperative hyponatremia had a 2.1-fold increased risk of complications, and those with pre- and postoperative hyponatremia had a 2.6-fold increased risk.

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 were asked to spend more days in the hospital after surgery. Patients with greater decreases in sodium after TJA were at higher risk of each of these negative outcomes. Hyponatremia was a significant risk factor for patients undergoing both primary and revision TJA.

For patients with preoperative hyponatremia that normalized after TJA, outcomes were similar to those of patients who had normal sodium levels both preoperatively and postoperatively. Contrary to popular belief, patients who had postoperative hyponatremia and had it treated before leaving the hospital stayed longer and had worse results than those who did not have it treated.

The study is in addition to previous evidence that hyponatremia is relatively common following TJA and can severely affect the patients’ postoperative period. "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 assert that low serum sodium levels could be a sign of deteriorating general health and an inadequate physiological reserve.

"Patients with preoperative and postoperative hyponatremia were particularly at risk," the researchers suggest. They emphasize the necessity of additional research to determine whether hydration guidelines and other "medical optimisation" measures can lessen the negative impacts of low sodium levels in patients receiving TJA.

(with agency inputs)