I Had Total Knee Replacement Surgery Almost A Year Ago.

i had total knee replacement surgery almost a year ago. i have continued to have issures on the same knee laterally, despite physical therapy, steroid injections. I am not overweight. i do not have swelling. I am presently taking celebrex 200 mg. once daily, and tylenol 500 mg. prn. I did have an knee scope 5 months prior to tka. My question is why do I still continue to have pain. I don't have pain everyday. But when I do it can get rather uncomfortable.