In this photo taken Wednesday, Sept. 12, 2012, Dr. David Mathis gives a cortisone shot to the knee of inmate Edwin Bergman at the California Medical Facility in Vacaville, Calif. Mathis

 

              In this photo taken Wednesday, Sept. 12, 2012, Dr. David Mathis gives a cortisone shot to the knee of inmate Edwin Bergman at the California Medical Facility in Vacaville, Calif. Mathis
In this photo taken Wednesday, Sept. 12, 2012, Dr. David Mathis gives a cortisone shot to the knee of inmate Edwin Bergman at the California Medical Facility in Vacaville, Calif. Mathis, a board certified physician, was the highest paid prison doctor in the state last year, earning a base salary of $239,572 and an additional $169,548 for working overnight shifts, weekends and holidays. Prison doctors say they are worth the higher pay because they face the constant threat of assault from inmates. (AP Photo/Rich Pedroncelli)