Smokers have worse outcomes after knee surgery than non-smokers, including less-complete healing and more surgical complications, according to a new analysis.
Smoking has a profound effect on circulation, "so that means it even affects musculoskeletal healing," said Dr. Kurt Spindler, an orthopedic surgeon at Vanderbilt University in Nashville, Tennessee, who wasn't involved in the new research.
Dr. David Flanigan, one of the authors of the review paper and a sports medicine doctor at The Ohio State University in Columbus, said surgeons had a hunch smoking was related to worse outcomes after knee surgery.
He and his colleagues wanted to get a sense of what studies on the topic had found.
They gathered the results of 14 studies, eight of which looked at surgical repair of knee ligaments, including the anterior cruciate ligament (ACL), and six of which examined repair of knee cartilage.
The studies looked at a variety of outcomes, such as how well people were able to get around after surgery, whether they could return to sports and if the surgery was considered to have excellent results.
All but one of the studies on ACL surgery found smokers tended to do worse afterward, the researchers report in The American Journal of Sports Medicine.
For instance, smokers were less likely to return to their pre-injury level of sport and experienced more pain. One study from the University of Pittsburgh School of Medicine found surgery patients who smoked were 64 percent less likely to report a successful outcome than non-smokers.
The one study that did not find any difference between smokers and non-smokers examined patients' risk of developing osteoarthritis in the knee.
Four studies on cartilage surgery found that smokers were less likely to have excellent results after surgery, had less improvement in the knee years later or had fewer beneficial proteins in the knee fluid than non-smokers.
In contrast, two studies found no differences between smokers and non-smokers on measures of pain and function.
There are about 150,000 ACL injuries in the United States every year, according to the American Orthopaedic Society for Sports Medicine.
Flanigan said he wasn't able to quantify just how much worse smokers tended to fare after surgery than non-smokers overall.
"We don't have a percentage to point to. I say (to patients), we do know this has increasing rates of failure, increasing rates of people not doing well compared to people who are not smokers," he told Reuters Health.
The individual studies also couldn't prove that smoking, itself, was responsible for the negative outcomes seen in smokers.
Flanigan said he'd like to see more research on the biology of smoking and knee repair to determine what is causing those worse outcomes.
Spindler told Reuters Health the consistency of the studies' findings implicates smoking.
"It makes me believe this is a powerful variable that does influence your outcome," he said.