Patella Disintegration 10 years after TKR

Saw new doctor for problems with my knee 10 years after TKR : pain sometimes severe, catching, slippage followed by excruciating pain on weight bearing relieved only by sitting. I had actually scheduled revision surgery but this new doctor is concerned that may not fix the problem as he does not see anything the matter with the prosthesis on X-ray or MRI ( nor did the other doctor see anything significant). He has ordered an 3 Phase bone scan as he is concerned there may be deterioration of the patella . Anyone experience this?