More than 300,000 patients in the United States seek emergency care for kidney stones each year, with the costs of treating kidney stones estimated at $2.1 billion.
Riding a moderate-intensity roller coaster can facilitate passage of small kidney stones, according to a report published today in The Journal of the American Osteopathic Association that attempts to corroborate patients' accounts of spontaneously passing kidney stones after riding a specific Disney World roller coaster.
In an expanded follow-up study, his team found a 70 percent passage rate when sitting in the back of the roller coaster.
"Imagine giving birth to a porcupine", says David Wartinger, professor emeritus at the Michigan State University College of Osteopathic Medicine, describing what it's like to pass a kidney stone.
Kidney stones form when minerals, usually calcium, accrete in the kidneys and begin to form jagged lumps. These stones will eventually move from the kidney down into the bladder and eventually out through the urethra.
Hundreds of thousands of people head to the emergency room every year for painful kidney stones, but new research suggests some could find relief at Disney World instead. In one case, a patient said he passed one kidney stone after each of three consecutive rides on the roller coaster.
Lithotripsy, which breaks apart kidney stones that are too large to pass, is a common treatment for the problem. Sufficiently convinced, he chose to test out the therapeutic coaster for himself.
"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", Wartinger said.
Wartinger did what any medical professor would do: He printed a three-dimensional model of the kidney that passed three stones, together with the three stones, all in clear silicone.
A silicon cast of the inside of a kidney in the office of Dave Wartinger.
"In the pilot study, sitting in the last auto 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", Wartinger said.
The model held three actual kidney stones of various sizes positioned in the upper, middle or lower passageways of the kidney.
Wartinger thinks that sitting in the back on this particular ride helped because the last vehicle ended up going faster down the inclines and around turns.
"The problem though is lithotripsy can leave remnants in the kidney which can result in another stone", Wartinger said.
While Big Thunder Mountain may have hit the sweet spot for one patient, Wartinger says that the correct combination of twists, turns and bumps will differ for each person. The inner structure of a kidney looks like a vast river delta with a series of branches all leading into a main chamber, and these branches look different for everyone. "It's not a violent roller coaster", said Wartinger.
"Preliminary study findings support the anecdotal evidence that a ride on a moderate-intensity roller coaster could benefit some patients with small kidney stones", Dr. Wartinger said.
The Magic Kingdom Park's Big Thunder Mountain Railroad is now closed for upgrade, due to reopen in November.
The researchers also took the test kidney on a low-key railroad ride around the park so they'd have a control arm to the study. The goal of this initial study was to validate the effectiveness of the model and support the case for further research.