CHICAGO — A surprising study of nearly 46 million Medicare patients says older residents in rural areas are more likely to have any of nine common surgeries than people in cities.

Back surgery, hip and knee replacements, and prostate removal were among the operations performed more often in rural Medicare patients, the study found. Emergency surgeries and elective operations alike were more common among rural residents.

The results seem to challenge the idea that city dwellers have better access to medical care, but experts say the research raises more questions than it answers.

“When I first saw the result, I looked at it and said maybe I got it backwards,” said lead author Dr. Mark Francis, a researcher at Texas Tech University Health Sciences Center in El Paso. The study doesn’t indicate where rural residents had surgery. It’s likely many had to travel some distance, which would be risky when urgent surgery is needed.

The study didn’t report on how the patients fared after their operations. Nor did it say whether rural residents had worse health overall than city dwellers, although some previous research has suggested that is generally true.

The authors say their findings could mean that rural residents are sicker, getting treatment they don’t need, or more likely to delay treatment for aches and pains until they worsen and require surgery.

It’s also possible rural residents have less access to non-surgical treatments, or view them as less desirable. But the real reasons can’t be gleaned from the study, which was a data analysis on all Medicare patients in 2006.

Though the cases are five years old, Francis said the results likely reflect current practice and noted that he had found similar trends going back to the 1990s. He said it’s unlikely the recession had much impact because these patients are covered by Medicare.

The researchers used ZIP codes and a government classification system that designates regions on a 10-point scale, with 1 being the most urban and 10 the most rural. They compared surgery rates among residents in regions 7 to 10 — the most rural — with the most urban areas.

The study was released Monday in the Archives of Surgery.

Francis said colleagues told him, “If you find a 5 percent difference, that would be a big difference from a public health policy view.” But the contrast between the two groups was larger than that for all but one of the operations — abdominal aortic aneurysms.

Rural residents were almost 20 percent more likely to have heart valve replacements, and about 15 percent more likely to get knee or hip replacements or spine fusion surgery. Smaller but still noteworthy differences were found for prostate surgery, appendectomies, surgery to remove neck artery blockages, and surgery to fix broken hips.

An Archives critique says the study raises hard questions.

“We have been led to believe that patients in rural areas lack appropriate access to surgery. Although this may be true for specific areas, it does not seem to be true for the nation as a whole,” Massachusetts General Hospital surgeon Dr. George Velmahos wrote.

Dr. Sam Finlayson, a Dartmouth Medical School surgeon and researcher, called the results provocative but said, “I don’t think this study can negate all of the evidence that there are pockets of problems with access to surgical care across rural America.”

Other research has suggested there’s a growing shortage of surgeons in rural America. But Keith Mueller, a rural health expert at the University of Iowa, said the new study raises the “so what?” question if people lacking local access can get surgery elsewhere. Even so, he said, it still may be more appropriate to have more of those services locally.