Thanks for your query.Knee pain
could be due to osteoarthritic changes in knee. these not seems to be related to hip replacement
before.But it is too early to say that you are suffering from this condition, without a proper clinical examination by an orthopaedician. Visit your doctor, get yourself examined. Your doctor will advice you to go for a xray.
I do hope that you have found something helpful and I will be glad to answer any further query.