A woman in Illinois decided to share a personal story about why she has 10 fingers but only nine knuckles. It’s because she was born with the Type E version of a genetic disorder called Brachydactyly. (Brach-a-DACT-alee.)
It makes fingers or toes shorter. In her case, her left ring finger is pinky-sized, and it has no knuckle. That finger and her middle finger are attached to the same knuckle.
Source: ViralHog