Ambulatory surgical center owners much more likely to operate on stones

"We found an association between ownership and the higher use of surgical services for the ambulatory treatment of stone disease," said first author John Hollingsworth, III, MD, chief urology resident at the University of Michigan working with Brent K. Hollenbeck, MD, MS, and colleagues. "We found that owners tended to treat a healthier population than non-owners. We also found that provider surgery rates rise with increasing competition in any given health care market."

Dr. Hollingsworth pointed out that the study was observational in nature, and the researchers were unable to show any causality.

The conclusion published in the study abstract raised an important question: With growing societal concerns about our country's health care expenditures, are these observed trends re-sponsible?

"There are a variety of explanations," Dr. Hollingsworth said. "It might be a misalignment of incentives and perhaps physician-induced demand, or it could just as easily be that the ambulatory centers provide more efficient care. Physician-owners may be able to provide quicker and more expedient care for their pa-tients."

Nevertheless, the differences are striking. The Michigan team chose Florida as the target of the study because of the availability of data. They focused on stone surgeries because Florida is at the heart of the so-called "stone belt." Using data elicited from the State Ambulatory Surgery Database for the period 1998 to 2003, the investigators identified all ambulatory surgeries for stone disease, noted which surgeons also were owners based on the proportion of surgeries conducted at ambulatory centers, and compared owners with non-owners on the basis of their case mix and volume.

This established that 1,520 owners and 3,086 non-owners performed 58,246 and 59,551 stone surgeries, respectively. The rate of surgeries for owners was 0.06 per 1,000 population compared to 0.019 per 1,000 for non-owners (p<.0001). This translates to a 316% increase of physician-owner surgeries over non-owner surgeries.

"There is also a statistically significant difference [p<.0001] between non-owners and owners from a patient disease perspective. Physician owners were tending to treat healthier patients," Dr. Holl-ingsworth noted.

Another curious finding was that stone surgery rates in a given market area increased when the number of ambulatory surgery centers increased. That data showed that each 10% increase in the surgeon-owner population corresponded with a 0.9 per 1,000 increase in the surgery rate.