Assessment of patient, Radiology and correlation with symptoms is important. Clinical examination essential for any answers.

Post the xrays.you will get a proper answer however the answer to your question is TKR gives nearly 80 to 90 percent of pain releif if done in good hands. And your dad will be excited after this

Treatment of knee osteoarthritis varies with functional disability of patients and my advise  is different based on the individuals expectations

TKR is suggested for giving pain relief and improved mobility. Generally, there is no treatment to 'cure' osteoarthritis. The treatment is mainly aimed at relieving symptoms. If he's having too much pain despite tablets and his activities are progressively reduced because of knee pain then TKR is a good option. It is a fairly successful surgery and generally chances of problems are quite less if done well

100 %

Yes, earlier stages of osteoarthritis can be treated without surgery very successfully. Once the entire joint is destroyed the only option is TKR.

Please share your fathers X-ray so the severity of arthritis can be assessed. In early stages medication and exercise may help In advance stages of osteoarthritis , surgery is the best way to relieve pain and improve the lifestyle and make patient independent