Nicotine constricts blood vessels, so wounds get less oxygen and healing nutrients, slowing and perhaps interfering with healing, says Adolph V. Lombardi, MD, president of Joint Implant Surgeons and lead author of the hip implant study. “Smokers may be getting as much as 25 percent less blood to the wound than nonsmokers. And bone healing is critical to this surgery, which requires the bone to grow into the implant,” he explains.

With less blood flow, the wound also receives fewer protective white blood cells, adds Dr. Lombardi. “So smokers are at increased risk of infection,” he says. 

Dr. Lombardi speculates that nicotine’s restricting effect continues to some extent even after people quit, explaining why past smokers don’t do as well as people who have never smoked. Still, he found that patients who quit smoking before and during their treatments had less pain and better outcomes

Michael A. Mont, MD, one of the authors of the knee replacement study and director of the Center for Joint Preservation and Replacement, offers two other mechanisms by which smoking can interfere. He says that carbon monoxide also affect blood cells, decreasing oxygen delivery to tissues, so that the tissues are more apt to die.

“Smoking may also increase cause blood platelets to stick together more than usual, which can cause blood clots,” he adds.

People with arthritis – both osteoarthritis, or OA, and rheumatoid arthritis, or RA – are among those most likely to receive a knee or hip replacements. According to a 2008 study in the Archives of Internal Medicine, for instance, the prevalence of hip OA is about 7.5 percent and knee OA about 12.2 percent. The study found that hip replacement would be appropriate for almost 38 percent of the men and 53 percent of the women. And according to a 2008 study in Arthritis Care & Research, as the incidence of RA rises, so do hip and knee replacements.

For people with arthritis, whose health is already compromised and who may very well face replacement surgeries, smoking adds unnecessary and serious risks.

The link between smoking and worse outcomes in arthritis is well established. Previous studies, for instance, have linked smoking to new cases of rheumatoid arthritis as well as worse outcomes in people who have it. According to a Swedish study at Malmo University Hospital, presented at the 2009 annual meeting of the American College of Rheumatology, researchers found that smoking increased the risk of a person developing rheumatoid arthritis. And several studies have shown that people with RA who smoke tend not to respond as well to treatment.  For instance, a 2011 study at Karolinska University Hospital in Sweden published in Arthritis & Rheumatism found that smokers were 50 percent less likely to respond well to treatment during early RA than nonsmokers.

Quitting’s not easy, but it’s worth it, says Dr. Lombardi. “The effect of nicotine may persist, but obviously it will [lessen] if you stop.”