What causes bone tuberculosis ?

Extrapulmonic TB: When you first get TB by inhalation it multiplies in the lung, then into a lymph node, where it ruptures into a blood vessel and the bacteria spread to sites around the body, usually those that receive the most blood. This includes bone. It may lie dormant in those sites for many years, only to reactivate later and produce disease at one of these extra-pulmonic sites.