THE EMPLOYEE WAS CHANGING THE SCREEN ON THE VIC. AS HE HANDLED THE SCREEN OFF TO ANOTHER EMPLOYEE INSIDE THE UNIT, THE INJURED EMPLOYEE FELT HIS ARM SNAP AND POP. THERE WAS A LOT OF BUILDUP IN THE AREA MAKING IT DIFFICULT TO MAINTAIN A FIRMBALANCE. ALSO, A LADDER WAS PLACED AGAINST THE SCREEN HOUSING THAT SHOULD HAVE BEEN MOVED OUT OF THE WAY.