I have hairline crack in 5th sacral vertebrae. What exercises of the extremities should I do to prevent formation of clots?

Clots? Unless u have a propensity for clots, this fracture shouldn't increase your risk of them. The sacral vertebrae are all fused together and rigid. Jogging or other impact activity would be painful and could displace the fracture. Concentrate on walking, yoga (avoiding seated asanas)and possibly supine exercise (pilates reformer) if not too painful until healed.