What Causes Knee Pain And Problem To Move After Replacement?

I HAD A TOTAL KNEE REPLACEMENT 10 YEARS AGO. I WAS TOLD BY A SURGEON THAT THE KNEE WAS NOT DONE CORRECTLY. THE ANGLE OF MY LEG IS WAY OFF. NOW I AM EXPERIENCING A PROBLEM WHERE THE KNEE ACTUALLY GOES OUT OF PLACE. I AM NOT ABLE TO WALK UNTIL I MOVE IT BACK INTO PLACE AND THIS IS VERY PAINFUL. WHAT COULD CAUSE THIS PROBLEM.