EMPLOYEE AND 1 MAN WERE CARRYING WOODEN PROPS AS A TEAM. THE MAN IN THE REAR STUMBLED WHICH CAUSED HIM TO STEP AWKWARDLY TO KEEP FROM FALLING. HE FELT PAIN IN HIS KNEES BUT HE FINISHED THAT SH IFT AND 2 MORE. THE PAIN GOT WORSE SO HE WENT TOTHE HOSPITAL AND HAS BEEN OFF WORK SINCE THEN.