Cold abscess in chest wall is most common due to

Ans is 'a' i.e. T.B spine * Cold abscess is a feature of bone tuberculosis and spine is the most common site of bone TB (about 50%)Rib tuberculosis is very rare.These lines from Tuli further support the answer."Abcess or sinuses from the cervical or dorsal regions can present themselves far away from the vertebral column along the fascial planes or course of neurovascular bundles. Thus they may present in the paraspinal regions at the back in the posterior/ anterior cervical triangles, along the brachial plexus in the axilla, and/ or along the intercostal spaces on the chest wall." -Tuli, 2/e