Hello Shireen and thanks for writing in at HCM
The risk and time period of recovery depends on the condition and physical condition of the patient. If he is physically active, no heart and diabetic issue than it takes no time to recovery. Complication of anesthesia
is slight high in this age.
In my opinion first try all medication and physiotherapy
for pain and wait for improvement. If you gets no relief than you must go for knee replacement
. Don't wait for too long because it can effect the other knee also.
If your father is physically active and pain is worse than go for Knee replacement otherwise you can take decision by keeping the pain in mind.