50 Years of Knuckle Cracking Did Not Produce Arthritis

Warned by relatives that knuckle cracking causes arthritis, Donald Unger decided to crack only the knuckles of his left hand. For 50 years he frequently cracked his left hand, never his right. Finally he wrote a letter to a scientific journal (in which he calls himself “the author”) pointing out that he did not have arthritis in either hand, supporting the conclusion of another study which studied a much smaller amount of knuckle cracking.

Thanks to Bryan Castañeda via Now I Know.

8 Replies to “50 Years of Knuckle Cracking Did Not Produce Arthritis”

  1. The National Institute of Health website has links to many published studies which show little or no harm from long-term knuckle cracking.

    However, according to a 1990 report (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1004074/):
    “Habitual knuckle cracking was associated with manual labour, biting of the nails, smoking, and drinking alcohol.”

    Just wondering: Does Donald Unger drink, smoke, bite his nails, or do manual labor?

    Seth: Unger’s study was better controlled than any of the NIH studies, in the sense that the hands being compared were identical in terms of diet and genetics.

  2. This whole thing is, of course, a joke. It is one of the recipients of the 2009 Ig-Nobel Prizes.

    Seth: Calling someone’s 50-year project “a joke” is not terribly nice. What do you mean by “a joke” and how do you know it is “a joke”?

  3. Unger’s letter is light-hearted and whimsical (“spinach-eating”!) and the authors of the previous study answered in kind. So in a way it is a joke, on both their parts. More like a case study so of course it’s statistically ‘underpowered’.

    Seth: “Joke” usually means “didn’t actually happen” (“I was joking!”). I see nothing to suggest that what Unger described didn’t actually happen. In fact, I believe Unger — like most of us — is not creative enough to make such stuff up.

  4. Seth,

    You’re right. I don’t know whether the 50-year “self-controlled study” actually happened or not. It’s certainly not impossible but fifty years of one-sided knuckle cracking seemed unlikely to me. The letter and response read like satire to me. The response is certainly satire, especially the “statistical analysis” of Dr. John Adams, e.g., “Typically, sample sizes of roughly twice the available research budget are required for valid inference.” (Not seeing a journal name at the top or bottom of either page also made me suspicious.)

    If I had access to a medical library, I would see if the cited 1973 article actually exists (I’m so ignorant I don’t even know if there was a Western Journal of Medicine in 1973). If I was a hot shot Berkeley Psychology Professor, I’d call Dr. Unger and ask him personally whether the letter described something that had actually happened or was “a joke.”

    It is funny.

  5. As a very ordinary person, with access to the extraordinary Internet, I could google “Donald L. Unger.” There I would find a couple of stories that indicate the project was indeed real and not a joke.

    Probably should have done that before I commented 🙂

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