What does a mild upper thoracic curvature convex to the left mean? I also have mild wedging of the T11 and T12 vertebral bodies with loss of approximately 5% of vertebral height. Is this concerning?

Spinal alignment. Spinal alignment varies from person to person, and can change suddenly with a fracture, or be abnormal from a childhood curve, such a scoliosis. Since your findings are mild, they may be just your "normal" variation. That is, everybody is shaped a little differently, but it doesn't cause a problem for most. If you have pain, a change in your posture, or an injury, see a spinal specialist.