Knee replacement 9 months ago - still not right !!!!

Hi,

My Father whos in his seventies had a total knee replacement before
Xmas last year.

Since then, hes been back in for a manipulation, regurlarly attends
physio (twice a week).

However, his knee is if anything worse than before the operation. Its
still swollen, he cant bend it too much, and still very painful.

Is this something that can happen?

To complicate matters, hes also got blood problems - takes Warfarin.
And steroids for some other blood condition.