Kidney stones aren't anyone's idea of a good time, but treating them could be more fun than we think. The prescription? A day at Walt Disney World. Researchers from Michigan State University (MSU) have found that roller coasters are an effective way to dislodge kidney stones, with tests on a synthetic model showing a success rate for passing kidney stones of almost 70 percent.

The research comes from David Wartinger, a urologist at MSU who was inspired to test the theory after patients reported success passing stones just hours after riding Disney's western-themed Big Thunder Mountain Railroad.

"Basically, I had patients telling me that after riding a particular roller coaster at Walt Disney World, they were able to pass their kidney stone," says Wartinger. "I even had one patient say he passed three different stones after riding multiple times."

In what was probably one of the most fun studies ever conducted, Wartinger rode the coaster 20 times, taking with him a backpack containing a 3D model of a hollow kidney with three stones suspended in urine inside, each under 4 mm (0.16 in). And it actually did seem to work, although where in the train the patient sat had a significant effect on whether the stone was successfully passed.

"In the pilot study, sitting in the last car of the roller coaster showed about a 64 percent passage rate, while sitting in the first few cars only had a 16 percent success rate," says Wartinger.

Those results were backed up by an expanded study, which Wartinger conducted with MSU resident Mark Mitchell. Riding with several kidney models at once, the researchers found the success rate approached 70 percent in the rear car, and if the stones were in the upper chamber of the kidney, they were found to pass every single time.

Interestingly though, when the models were taken on other roller coasters in the park, the results were less impressive. Wartinger suggests that the G-force of faster rides might keep the stone in place. Instead, the ideal roller coaster for passing stones is one that's bumpy and twisty, but stays right-side up and doesn't go too fast.

"In all, we used 174 kidney stones of varying shapes, sizes and weights to see if each model worked on the same ride and on two other roller coasters," says Wartinger. "Big Thunder Mountain was the only one that worked. We tried Space Mountain and Aerosmith's Rock 'n' Roller Coaster and both failed."

While it's far from a clinical prescription, Wartinger says it's probably worth a try for patients with smaller kidney stones, or those who have undergone lithotripsy, a treatment used to break larger stones into smaller, more easily passed fragments.

"The problem though is lithotripsy can leave remnants in the kidney which can result in another stone," says Wartinger. "The best way to potentially eliminate this from happening is to try going on a roller coaster after a treatment when the remnants are still small."

The research was published in the Journal of the American Osteopathic Association.