One possible cause of your problem could be a muscle imbalance or weakness in the muscles around the knee.Many times the Vastus Medialis, which is the portion of the quad on the medial side of the knee. If you sit on the floor and extend the leg you can find the vastus medialis by flexing the leg and look for a teardrop shaped muscle just above the knee on the inside part of the leg. It can be overpowered by the larger quad on the lateral side of the leg. When that happens it can cause the knee to track incorrectly. I'm not saying that's your problem but it's something to consider and it's an easy fix.
I had a TKR last September and I can get out of the saddle to pedal without issue. MY knee is fine my back....well that's another story.