Dislocation of the veebra is uncommon in thoracic region because in this region:

In the thoracic and lumbar region of the veebral column the adjoining veebrae are maintained in position by the close interlocking of the aicular process. As a result dislocation in this region is highly uncommon and usually takes place after fracture of the aicular process. Interveebral disc herniation is more common in the lumbar region than cervical.The discs usually affected are those between fouh and fifth lumbar veebrae and between fifth lumbar and veebrae and sacrum. A lateral herniation may press on one or two nerve roots going to interveebral foramen just below.