How does the geometry of this joint work? I understand it has ovoid and elliptical surfaces, but not how they move wrt each other.

Is there only sliding, only rolling, or both?

Are the extension/flexion movements equivalent to simply rotating about the center of curvature of the "ball" on the metacarpal? How about the sideways movement?

Is this joint funtamentally different from an arthrodial, hinge or ball-and-socket joint?

Cheers.