Dear,
Firstly , I would suggest you to get Knee replacement only when the patient is ready for it as it requires a good post operative rehabilitation.
Secondly, get it done only when patient has symptoms such as severe pain, difficulty in walking etc clinically.
Not just a X-ray picture is suggestive of arthritis.
Third, select a doctor first whom you want to do a surgery and then decide hospital.
Next Steps
Visit the hospital yourself and talk to doctors.