T12 (12th Thoracic Vertebra) The twelfth thoracic vertebra (or the T12 vertebra) is the largest and most inferior of the thoracic vertebrae. T12 bears the most weight of any thoracic vertebra, making it the strongest thoracic vertebra, but also the most susceptible to stress-related injuries. In many ways, the T12 is a hybrid vertebra with the ....