One is a difference in the methods used to determine the glycemic status of patients with diabetes. Previous researchers relied on diagnostic codes, whereas the Kaiser team looked at actual laboratory tests as well as codes. They also used data from the large Kaiser Permanente Total Joint Replacement Registry to validate surgical outcomes.

Another possible reason for the different results is that the Kaiser patients with diabetes were healthier and their outcomes better overall.

“Except for rehospitalization, all the outcomes we studied were rare in our population,” Adams says. “Patients with poorly controlled diabetes were also rare – even when we tried changing the definition of glycemic control.” She notes that the rarity of both makes it harder to draw statistically significant conclusions.

Still, Adams says the evidence clearly suggests that factors other than blood sugar levels are responsible for postsurgical complications in patients with diabetes.

“I think multiple factors are involved. Diabetes can have a trickle-down effect on many body functions and organs, so it is not operating in isolation. There are other things [such as obesity] that are interacting with it,” she explains.

Kaiser researchers undertook the study because more than half of all diabetes patients also have osteoarthritis (OA), and may eventually need joint replacement surgery, Adams says.

“Diabetes matters, and doctors and patients need to be mindful of the presence of diabetes when considering major surgery,” she says. “But it is not the only factor in play, and glycemic control as we defined it does not appear to lead to poor surgical outcomes.”  

Osama Hamdy, MD, PhD,  medical director of the Obesity Clinical Program and clinical investigator at the Joslin Diabetes Center in Boston and an assistant professor of medicine at Harvard Medical School, is not convinced.

“Although this study suggests that you don’t have to postpone elective surgery for total knee replacement if diabetes is uncontrolled, it’s important to remember that this is a retrospective study that is missing [some] very crucial information, such as the type of diabetes treatment, duration of diabetes and the status of diabetes control during hospitalization when [insulin therapy] can rapidly improve blood glucose levels,” he says.

In addition, he says, the study didn’t look at more common complications among hospitalized diabetes patients, such as urinary-tract infection, hospital-acquired pneumonia and acute renal failure.

“Finally, the study didn’t look at length of hospital stay, which is frequently longer if diabetes is uncontrolled,” says Dr. Hamdy. “I think the study is not giving us the whole picture, and we should take its conclusions cautiously until we have a prospective, randomized controlled study.”