It is what my PT person says is a good hurt...
Yes, correct IMO (well it was the same for me, anyway). It's because the tendons at the back of the knee aren't, again IMO, damaged in surgery.
However. Here's a lot more IMO, although I have read a lot about this: if you do a stretch into pain, the body reacts against it and tenses up. This is not productive. A stretch should be perhaps 30sec long, to the point of pain but not into it, with multiple repetitions. You can see in my exercises thread (link below) pix of the extension stretch I did, or you can try this one, with a partner.
- You sit on the floor, TKR leg out straight.
- Rest the heel on a fairly thick book or similar, to get it may 2" off the ground
- partner kneels at right angles to your leg, placing one hand about 6-9" below the knee, one about 6-9" above.
- gently pushes the leg towards the floor until you feel a good stretch through the back of the leg
- holds for about 20sec
- eases off, waits 30sec, repeats.
- repeat 3 or 4 times.
It's effectively the same as the self-performed exercise pictured in my thread on the subject, but more effective IMO.