An employee was walking down concrete steps from a 19" concrete platform. On the last step, the employee's left foot stepped on the front edge of the step, causing the employee's right foot to roll. He lost his balance and continued to step down. His body and leg moved in a twisting motion, causing a break in his right tibia as his right foot impacted the ground. He did not fall down. He then sat down on the step and radioed for help.