After my second TKR, at the one year follow up we were talking with my surgeon and the subject of kneeling came up. I was not having subcutaneous pain but a friend was, I asked the Dr. why neither one of my knees hurt when a friends. His reply was that I should look at the scar on my knee(6.25" w/32 staples for closure) and then friends scar. The Dr. explained he cut as far off center to the outside of the knee as possible and he would bet my friends scar was in the center of the new patella.
Sure enough, about 3/4 of an inch off. He said that was far enough to keep the pain to a minimum when kneeling.