British Journal of Sports Medicine has an excellent case report which describes a Broken arm wrestler:
"Usually the musculotendinous structures are the limiting factor in arm wrestling, but in this particular case they were not, either because the proprioceptive awareness of the patient was reduced because of the alcohol and late night and/or he wasovermuscular for his bony size, in the sense that, although he was generally muscular, he did not have the humeral cortical bone hypertrophy to match his muscularity because he was not a regular arm wrestler.
This type of arm wrestling injury tends to occur when one arm wrestler tries to force the match in an effort to win or to change the tide of the contest. As the offensive wrestler continues with the attack, the defender's internalrotator shoulder muscles suddenly and passively stretch and change from their maximally concentric contraction to an eccentric compensatory contraction, resulting in an intense rotational force with subsequent humeral fracture."
Video: An arm wrestler breaks his arm during a match at the Empire State Golden Arm Tournament of Champions in New York City. There is a clearly audible snap in the video when the humerus breaks.
John Brzenk, who is considered the best arm wrestler in the world, responds to a fan question regarding how often (professional) arm wrestling leads to fractures:
"To be honest over the last 15 years of arm wrestling I’ve seen maybe a handful of broken arms and all of them in the upper arm."
Any fracture is serious. If you engage in arm wrestling, please have the cases above in mind, exercise properly and take every precaution to prevent similar injury from happening to you.
Broken arm wrestler. Br J Sports Med 2000; 34:461-462.
Interview with John Brzenk. ArmWrestling.com.
Image source: Arm wrestling from Wikipedia, the free encyclopedia.
Ed Goljan, M.D., professor of pathology and top notch arm wrestler