The carpal boss is a bony part that sticks out of the back of the hand, called the dorsum, at the second and/or third finger joint. Researchers aren’t sure what causes it, whether it’s caused by trauma or that it’s degeneration of bone. They also don’t know how common it is. Osseous coalition is the joining of bone. The authors of this article examined the presence of the carpal boss on 202 wrists of cadavers (bodies) to see if they could determine the incidence and the presence of osseous coalition, and how often it appears.
The researchers dissected 87 pairs of wrists. They examined the anatomy of the wrists when they were in the neutral or bent position and then again extended. They were looking for a visible and palpable (one that could be felt) prominence on the back of the hand.
Thirty nine wrists out of the 202 had the bony prominence and all wrists with the bony prominence also had at least a partial osseous coalition. Ten pairs of wrists had it in both wrists. the osseous coalition was found between at the base of the third finger, the second finger, or between the second and third fingers. None was noted in the other joint areas.
The authors wrote that their study confirmed the high percentage of partial osseous coalition with carpal boss, but they still don’t understand what causes it.