Steroids are not recommended for people with diabetes for this exact reason. The sugar spike could last up to a week. Be very careful with your diet. Definitely tell your doctor immediately.
I'm assuming the steroid shot in your knee was because of knee pain that wouldn't go away? Ask to see if there's anything else that can be done to help without steroids.
You could also give your doctor a call already to let him know the situation and to get instructions.
Hi, steroid shots can definitely cause a peak in blood sugars, that may take a while to subside.
For the meantime please drink plenty of water and avoid eating carbs /' sweet foods as much as possible (no breads, rice, cakes, candies, icecream, tropical fruits aetc), just stick to veges (non starchy) and meats.
If your sugars are still high in 24 hours please contact your doctor for further instructions.
I unfortunatley found that my diabetes was irreversibly worsened after some oral steroids. However, hopefully your sugars will return to normal in a few days once the steroid is out of your system.