More than 16 million people in the United States are affected by diabetes, a metabolic condition resulting in high blood sugar levels. A new research article published in the June 1, 2018 issue of the Journal of the American Academy of Orthopaedic Surgeons, examines how levels of hemoglobin A1c (HbA1c), affects the risk for postoperative wound complications and deep infection after shoulder replacement in patients with diabetes. HbA1c levels reflect the control of blood sugar.

“While diabetes has been strongly associated with an increased risk of wound complications and postoperative infection after total hip and knee arthroplasty, it has not been routinely associated with higher rates of infection after shoulder replacement,” says lead study author and resident orthopaedic surgeon Jourdan M. Cancienne, MD. “With the number of shoulder replacements in patients with diabetes expected to increase, as well as the costly consequences of wound complications and infection, it is of high clinical significance to determine if these patients are at an increased risk for infectious complications postoperatively.”

To examine the association between preoperative HbA1c levels and the risk of deep postoperative infection after shoulder replacement in patients with diabetes, the study authors identified 18,729 patients who underwent shoulder replacement between 2007 and 2015. Of those patients, 8,068 were diagnosed with diabetes and 2,537 of them had their HbA1c levels tested within 3 months of their surgery date. The authors then looked at the rate of wound complications within 6 months of surgery and deep infection within 1 year of surgery and highlighted the following findings:

•Patients with diabetes had a 1.4% risk of infection with 0.7% risk for deep infection, and those without diabetes had a 0.9% risk of infection with 0.4% risk for deep infection. The increased rate of infection in the diabetes cohort was statistically significant and demonstrates the increased infection risk associated with diabetes.

•As the pre-surgery levels of HbA1c measured increased, so did the risk of wound complication and deep infection.

•A pre-surgery HbA1c level of 8.0 milligrams/deciliter could serve as a threshold for a significantly increased risk of deep infection following a shoulder replacement.

According to the research article, there were several limitations to this study, including the use of HbA1c levels as an indicator of blood sugar measurement, as these tests could be inaccurate in patients with other conditions affecting the blood. Additionally, the study used a large administrative database, which relies on the quality of the data and accuracy of the coding entered.

While study authors used a multivariable regression analysis (a tool that uses multiple variables to forecast possible outcomes) to limit the effects of confounding factors, the database used was unable to control for surgical time, indication for surgery, the use of antibiotic cement to manage infection, surgical technique, and number of surgeons during the procedure, all of which may contribute to infectious complications.

“Further research is needed into the tools used to measure blood sugar levels and into the conditions associated with diabetes that place these patients at a higher risk for infection,” explained Dr. Cancienne. “Patients with diabetes and HbA1c levels of 8.0 and higher should be counseled that proceeding with surgery may place them at higher risk for prosthetic joint infection.”