Can't decipher those letters that follow your doctor's name? If you can't tell a D.O. from an O.D., refer to this quick checkup on credentials.  D.C.: doctor of chiropractic Translation: Unlike an orthopedist, who is an M.D. and prescribes drugs or surgery for back pain, a chiropractor physically manipulates a patient's spine for therapy. Training: After a requisite number of undergraduate class hours, three years and four months of chiropractic study are necessary. An orthopedist, on the other hand, after four years of undergraduate study, must complete four years of…