NEW FINDING: Migrating to a new fortress removes naturally healing Injuries, but NOT NERVOUS INJURIES.
Explanation: two of my miners in a fort lost in a zombie invasion had their legs broken in a number of places, and infection was rapidly setting in. One of the miners had a broken spine, the other just had broken legs. I abandoned the fort just before they died, and now in this new fortress, a fortress that they migrated to in the third or so month of the year (two legendary miners in the first few months...excellent!) their legs seem fine.
However, the spine miner has the red flashing cross indicating a loss of walking ability. When I checked his injuries, his lower spine is blue, indicating loss of function. Most curiously, however, he seems to be getting around just fine, with no crutches and no crutch-walker skill. His background is brown, indicating he is crawling, but he seems to be crawling as fast as any other dwarf walks. I'm afraid that getting hospitalized will reveal he is unable to walk, but the game doesn't seem to care about that very much.
Seems like a bug of some sort? Much like the other fort where the dwarf had a lost leg and was walking at 100% speed with no crutches?
EDIT: Upon further reflection, the miner is in fact slower than other dwarves, but not by much. I think that his extraordinary physical stats as a result of being a 5-year legendary miner in the old fortress have enabled him to crawl along the ground at almost the speed of a regular dwarf. I suppose I could injure him, force hospitalization and diagnosis, and then have him diagnosed with crutches, but I'm afraid of hurting him even more.
As a fun note, this demonstrates that physical attributes as well as skills are moved over when dwarves migrate to a new fortress, proving that a dwarf from an old fort is 100% the same, down to the miserable condition these guys came in as a result of having just seen their friends torn to bits by zombies.