More physician-owned outpatient surgery centers may mean the surgical removal of more kidney stones, suggests a new study.

Because of declining reimbursement for their professional services, as well as rising practice costs, physicians' real-dollar incomes have been declining, lead researcher Dr. John M. Hollingsworth, of the University of Michigan Medical School in Ann Arbor, told Reuters Health in an email. In response to their new economic reality, physicians have sought nontraditional revenue sources as a means of generating extra income.

One of those investments, he added, is in ambulatory surgery centers -- medical facilities that perform surgeries not requiring an overnight stay.

Based on state-level data from Florida, Hollingsworth and his colleagues investigated what happens after one of these centers opens up in a health care market: How is business at nearby hospitals affected, and does the overall rate of surgery increase?

They looked specifically at the surgical removal of kidney stones, a common and painful urinary tract disorder that afflicts about 5 percent of the U.S. population and accounts for almost 3 million healthcare visits a year.

Most stones pass through the body without any medical help, but sometimes they stick around long enough to cause severe symptoms and complications that require intervention. However, setting the threshold for active treatment can be somewhat subjective, the authors note.

Drugs called alpha-blockers can induce the body to pass kidney stones more quickly. If time and medication do not eliminate the stone, several surgical procedures can be used to break up and extract stones. Lithotripsy, the technique used most often by ambulatory surgery centers in the Florida study, costs on average more than $17,000.

The team found more than 2,200 additional surgeries performed where an ambulatory surgery center opened between 2002 and 2006. This translated into an average annual increase of 11 procedures per 100,000 individuals.

Four years after a center's opening, approximately 64 percent more stone surgeries were being performed in its local health care market compared to a similar market without an ambulatory surgery center.

Meanwhile, it didn't appear that the centers were taking any business away from the competition: surgery rates at nearby hospitals held steady.

The researchers note the possibility that these ambulatory surgery centers were simply placed in markets with a real unmet need for more stone surgeries. Or the rise in stone surgeries could be the result of financial pressures on the urologists, they suggest in The Journal of Urology.

While barring physicians from referring Medicare and Medicaid patients to centers in which they have ownership, current federal law does allow physician investment in ambulatory surgery centers. The numbers of these centers are on the rise across the country.

Physician ownership can provide benefits to the patient, including convenience and less hospital time, but it might also reflect a financial conflict of interest, Hollingsworth said.

A separate study of insurance claims in the state of Idaho recently found that orthopedic surgeries, such as those performed on the rotator cuff or knee, also increased with physician ownership. (See Reuters Health report, August 18, 2010.)

To the extent that our findings and those of others reflect physician-induced demand, noted Hollingsworth, policy remedies may include revisiting the federal law that permits physician ownership.

SOURCE: The Journal of Urology, online July 20, 2010.