The thecal sac contains fluid, and surrounds (protects) the spinal cord.
Angulation usually refers to a type of injury or condition that has caused the bone (or other structure) to either be fractured or displaced.
Can you tell us more about your diagnosis? Did you sustain an injury to your back, or have a medical condition (you tagged this as degenerative disc disease)? Do you have any additional questions about treatment options (what information has your doctor provided to you?)