Looks like high grade of patellofemoral osteoarthritis . You can try intrarticular steroid injections but it may have mixed results in this stage. Still go ahead with intrarticular depoprednisolone injection and physiotherapy.

Your interest in not getting operations is not going to define the scientific line of treatment. Any other treatment will not help you in reducing the problem. If you want to make your father pain free for rest other life , Knee Arthroplasty is right answer. For detailed discussion and consultation kindly consult via pay Practo.