EMPLOYEE HAD HOOKED SWITCHER AND RAILCAR GLADHANDS TOGETHER. WHEN THE EMPLOYEE OPENED THE BALL VALVE TO APPLY AIR TO THE CAR, THE GLADHANDS BLEW APART. ONE OF THE GLADHANDS STRUCK THE EMPLOYEE IN THE KNEE. THE EMPLOYEE CONTINUED WORKING UNTIL THE PAIN GOT WORSE AND WORKMANS COMP. ALLOWED SURGERY. EE HAD NOT BEEN ON LIGHT DUTY AS EE DIDNT FEEL EE NEEDED IT.