Hi there. I'm happy to answer your question.
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I am an Orthopedic Surgeon and would like to help answer your questions. Please understand that the information that I provide is for educational and informational purposes and is not treatment or meant to substitute for being treated by a live physician. I get online once a day and therefore please bear with me if you post and I haven't responded yet. I will in due time. Please do not accept until you have had your question answered in a satisfactory fashion.
I'm sorry that you are having this problem with your knee.
It is unlikely that the PT made your arthritis progress from moderate to severe bone on bone. This doesn't happen overnight.
It sounds like the steroid shot worked from 7 months ago. That is a good sign.
Is your arthritis in the medial (inside) or lateral (outside) compartment of your knee only?
Usually arthritis starts on one side first. Are you bowl-legged or have knock knees?
If you have arthritis in one compartment of you knee rather than both and you are this young then you may be a candidate for a bony procedure called a osteotomy of the tibia or femur. What this can do is to offload the bad compartment of your knee to relieve the knee pain.
Regarding the rooster shot - you are in a lot of pain after it? When did you have the shot?
Which one did you get? There is a small incidence of inflammatory reaction and/or infection after that shot. If you are in worse pain and cannot walk after that shot then you should get checked out to make sure you are not having a reaction. You should not be in pain all day and night.
Please let me know some of these answers so I can help you more. Unfortunately your issue of gaining weight with inability to exercise is a common problem. There is no good solution but I can say that all weight loss must start with a good diet complemented by moderate exercise. Are you able to swim or bike without pain? Those are both non-weightbearing exercises that are easy on the knees. Thanks.