Donald Unger, an allergist in Thousand Oaks, California, earned the medicine prize for addressing another timeless question: does cracking knuckles really cause arthritis, as his mother warned him it would? As a child, he naturally thought his mother omniscient, but as a teenager he learned about science and started questioning received wisdom of this kind.
To resolve the issue Unger embarked on a long-term controlled experiment, and began cracking the knuckles on his left hand twice a day, but not those on his right (Arthritis and Rheumatism, vol 41, p 949). He has done so for more than 60 years, and never suffered arthritis in either hand.
As a non-experimental knuckle-cracker, this is research I appreciate.
For his work, Unger received the Ig-Nobel prize for medicine. Other prizes detailed here.