EMPLOYEE IS STATING HE WAS STEPPING BACK FROM FUELING A DOZER TO THE CONTAINMENT STRUCTURE AROUND A DIESEL FUEL TANK. HE LOST HIS BALANCE AND STEPPED DOWN TO A PLATFORM (APPROX 2') PUTTING HIS WEIGHT ON ONE LEG. THIS ACTION CAUSED AN INFLAMATION TO THE OSTEOARTHRITIC CONDITION OF HIS LUMBOSACRAL SPINE THAT HAS EXISTED FOR A PERIOD OF TIME.