There is something called as seronegative Arthritis in which RF and Anti CCP can be negative. Her Clincal examination is very important. Blood investigations are only supportive.

What is her age? It can be any Arthritis or can not be. History is important than the blood reports. Only raised ESR, without relavent history is not suggesting Arthritis

Hello , First of all , high ESR will never cause arthritis. Its a non specific marker of inflammation which can be raised in lots of disorders . In some patients and that too especially in females sometimes high esr is normal finding . As regards your patients knee joint pain , a x ray and a thorough examination will help us understand more abt the issue . Anyhow , unless she has some immune related arthritis which she doesnt seem to have , osteoarthritis at her age is very rare. I would suggest to apply some ice packs , start any anti inflammatory medicine and physiotherapy in form of quadriceps and hamstring exercises