I don't have a sister. Yes, that all fits. Your description fits a condition called splints. Sometimes horsemen say that a horse has 'popped' a splint. Yes, it's common.
Splints come in a few types.
First, the anatomy. The small bones are splint bones attached to the cannon bone by a thick ligament called the interosseous ligament. The splint bones are really remnants of toes from early evolutionary days when prehistoric horses had more than one toe. They serve as support bones now, which is where the name comes from. They act like splints on both sides of the cannon bone.