Even mild trauma can cause a disk to herniate---I don't even know what caused mine to pop out and wedge b/n my spinal cord and vertebra

With your other vertebra fused the T1 could have gotten the full force of the blow

From the MR report you likely have a new problem there--motion can render an MR useless--while CT myeography is painful, there are no closed spaces involved and you definitely need to find out if there is compression there

are you having sx?