Bunion and overlapping second toe
Great video, right? But why would this ever happen? Why would the second toe ride up and over the great toe? It all starts with a person's genetic predisposition to form a bunion.
Bunions aren't inherited per se, but people do inherit the same biomechanical set of bones and joints that their parents and grandparents have. And if there's a tendency for a family to have bunions, we tend to see that biomechanical trait passed down through the family.
Bunion - what causes a bunion?
A bunion is normal bone, it's just that the bone is in a poor position. The bump of bone we call a bunion is located on the head of the first metatarsal bone. The reason that a bunion forms is due to the fact that the first metatarsal is no longer straight, but over time changes in position becoming poorly aligned. The position of the first metatarsal makes the foot wider. In the process of creating a bunion, the first metatarsal moves away from the second metatarsal, essentially making the forefoot much wider. As the first metatarsal moves medially (away from the second metatarsal) the tendons attached to the toe continue to pull up and down on the toe. As the first metatarsal changes position, the tendons that move the great toe start to pull in a deviated position, tugging the great toe towards the second toe.
These same mechanical properties also make the second toe move towards the great toe. The tendons that pull the second toe up and down become poorly aligned and rather than simply pulling the second toe up and down, they now pull the toe in a medial direction, towards the great toe. The outcome is an overlapping toe that is difficult to fit into a shoe.
This video shows the early stages of the progressive deviation of the toes. In this case, the changes of the great toe and the second toe are flexible and return to their normal positions when done moving. Progressively though, over time these flexible deformities will become rigid and fixed with the great toe permanently residing under the second toe.