I thought cortisol was a catabolic hormone. So then if anything wouldn't it break down fat, I would worry more about my cartilidge if I were you. I wouldn't trust a physio to give me a cortisol shot unless I had got my own MRI and shown it to another consultant preferably one who has nothing to gain by prolonging my injury or by bringing it to a premature close at the cost of a long term performance decrement (ideally speak to a qualified freind or family member) and had a second opinion from him.
One final piece of advice, if your physio was an athlete or bodybuilder (recreational or otherwise) whoose career was ended by injury sack him the second you come by this information! Why?
1) The same principle as "never trust a bald barbour he has no respect for your hair".
2) If he couldn't prevent his own injury how in the blue hell do you expect him to be able to fix yours?