1, 2, 3. First degree sprain - is a tear of only a few fibers of the ligament. Second degree sprain - is a tear of part of a ligament, from a third to almost all its fibers. Third degree sprain - is a complete tear of the ligament. (source :wikipedia).
Graded 1 through 3. Sprains and strains are graded based on the number of fibers within the structure that are stretched/ torn. This is by no means an exact number (of fibers), st but a grade 1 = fiber stretch, grade two = partial/ moderate disruption, & grade three = complete disruption.
1, 2, 3. They are rated as 1st, 2nd & 3rd degree depending on the extent of injury.
Grade I, II, and III. Grade I sprain is the most common and requires the least amount of treatment and recovery. The ligament damage has occurred without any significant instability developing. Grade ii injury is more severe and indicates that the ligament has been more significantly damaged, but there is no significant instability. Grade iii sprain is results in torn ligaments resulting in instability.