Crack Research: Good news about knuckle cracking cracking knuckles https://www.scientificamerican.com/article/crack-research/ Crack Research: Good news about knuckle cracking http://www.scientificamerican.com/article/crack-research/ Source 1 www.scientificamerican.com/article/crack-research/ ♦ SOURCE ♦ SOURCE Donald Unger http://www.scientificamerican.com/article/crack-research/ ♦ SOURCE