Brief Answer:
Possible osteoarthritis of hip.

Detailed Answer:
Hello dear, welcome to Ask a doctor service.
I read your query and here is my advice.

I think the groin pain that you are having is not directly related to knee replacement surgery you had not a complication of it.
I think it can be related to another issue such osteoarthritis if the hip or even sciatica nerve pain.
You may need to do a x-ray of hip to see its conditions and if it has osteoarthritis too.
You may need to use any antinflammatory drugs such advil or naproxen for pain.

Hope I have answered the question.
Let me know if I can assist you further.

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