EE WAS PUSHING A 2-WHEELED CART LOADED WITH AN 02 BOTTLE INTO THE WELD SHOP. THE CART WHEELS CAUGHT ON AN OFFSET OF CEMENT INT HE DOORWAY CAUSING THE CART TO STOP SUDDENLY. THE SUDDEN STOP IMM ED THE CART INTO EE BODY. OVER AN OFFSET, EE SHOULD HAVE PULLED THE CART. ALSO EE HAS HAD PREVIOUS BACK PROBLEM