This is most likely abdominal wall paresis (lack of abdominal wall muscle ability to contract) from either nerve stretch or nerve compression. The thoracic spine contains all the nerves that cascade down to the belly to supply the muscles here. One nerve that is injured will do exactly what you have experienced, a band of weakness and a bulge of the abdominal wall along a descending band.
There are two things that you can do. One is to have a CT scan of the thoracic spine to see if a screw is out of place and irritating a thoracic root. The other is simply to wait and see if this nerve will heal. See the section on “Nerve Damage and Healing” to understand how nerves heal.