Aching knee and hip joints may hurt less after successful weight-loss surgery, a new study suggests.

"In particular, walking is easier, which impacts patients' ability to adopt a more physically active lifestyle," lead researcher Wendy King said in a news release from the ObesityWeek meeting.

Weight-loss surgery isn't a "magic bullet" for joint pain for every patient, however.

"Some patients continue to have significant pain and disability" even after the operation, said King, who is an associate professor of epidemiology at the University of Pittsburgh's Graduate School of Public Health.

King's team was to present the findings Wednesday at the ObesityWeek meeting in Los Angeles, which is hosted by the American Society for Metabolic and Bariatric Surgery and The Obesity Society.

In the study, the researchers tracked outcomes for more than 2,200 obese people, average age 47. All had undergone weight-loss (bariatric) surgery at one of 10 hospitals across the United States.

In the three years after surgery, 57 percent of patients who'd had significant mobility limitations before the procedure no longer had them, and about 70 percent of those who'd had severe knee and hip pain or disability had improvements in joint pain and function, the researchers found.

However, one in six patients still required narcotic pain medication, 26 percent still had problems moving around and there were wide variations in several measures of pain, disability and physical function, the researchers said.

Overall, however, "our study found that clinically meaningful improvements in bodily pain, specific joint pain, and both perceived and objectively measured physical function, are common following bariatric surgery," King said.

Certain types of patients -- younger, more affluent males in particular -- tended to do better after surgery.

Also, people who went into the surgery with a relatively lower weight did better than the very obese, King's team found.

"Obesity can affect the knees and hips and cause bodily pain because of all the added stress it puts on the joints. As a result, musculoskeletal problems are quite common among bariatric patients," Dr. John Morton, president of the American Society for Metabolic and Bariatric Surgery, said in the news release. Morton is also chief of bariatric and minimally invasive surgery at Stanford University School of Medicine in Palo Alto, Calif.

"Bariatric surgery can help reduce or reverse that pain and improve function, but the longer one lives with obesity, the less improvement one may have. In certain cases, some damage to the joints may be irreversible," added Morton, who was not involved in the study.

Findings presented at medical meetings are typically considered preliminary until published in a peer-reviewed journal.