Hi, thanks for writing to HCM.
A successful Primary Total knee arthroplasty
should not give rise to any sort of symptoms (especially pain) after a period of 3 months (maximum).
Also you should have attained a minimum of 100 degrees of motion in the knee joint ( which is not in your case -not able to bend knee fully). This byitself indicates that there is some problem in the knee.
I suspect HETEROTOPIC OSSIFICATION in you (as you are able to feel a lump above the knee cap) which results in limitation of movements of the knee.
Any pain or stiffness
after TKR warrants a detailed evaluation.
I suggest you to consult an arthroplasty surgeon and follow his advice.
Hope this information is helpful. Good day