"It's an interesting study, but it could have been better designed," he says. "They have no acceleration/deceleration data, which would have been very helpful in understanding the effects of specific G-forces required to dislodge the stones. A discussion about the effects of G-force and what is needed to dislodge a stone are needed to flesh out the findings."
The study also lacked a control arm, meaning the researchers couldn't compare results from the roller coaster to other interventions or, perhaps, no intervention at all, according to Faerber. "Who knows, maybe just walking around the park or taking the monorail to the park also resulted in migration of stones. Unfortunately, the study didn't answer this question."
Kidney stones are formed by a number of causes including dehydration, excessive sodium, and metabolic factors. Once they form, the stones must make their way out of the kidney, through the ureter, and into the bladder to be passed. The roller coaster G-forces may play a part in making this migration happen. "Both positive and negative G-forces might play roles in freeing up the stone fragments," says Faerber. "Positive (downward) motion might accelerate the fragments down the ureter portion and negative (upward) motion would help lift the fragments from the lower part of the kidney up and over the 'lip' into the pelvis."
While that sounds technical, you can recreate a similar situation at home. You don't even need a rollercoaster or 3-D printed kidney. Simply put some M&Ms in a bottle and start shaking. "Ultimately the more you shake, the more likely you'll be to get them out," says Faerber. "Or think of a piggy bank—shaking it to get all of the coins out. Maybe a vigorous percussion massage might do the very same thing and might be a bit cheaper than a one-day ticket to Disney."
Of course, a kidney is very different from a bottle of candy or a bank full of coins. The human kidney is adhered to other structures inside the body. Also, the ureter isn't simply a hollow tube. "A better experimental design would be to take measurements of the forces on the ride and then simulate the up and down surges in an animal model using a real kidney and ureter."
"Right now all that they have shown is that if you rattle a container with little rocks forcefully enough you can get some to tumble out of an opening," says Faerber. "It's probably not really translatable but it makes for good copy."