I had knee replacement surgery on Tues (Sept 3) and am home from the hospital. After the surgery my blood sugar went berserk. I had numbers in the 170-315 range for 42 hours, starting about 6 hours after the surgery. The hospital's diabetes specialist said that the body produces its own steroids after surgery to compensate for the trauma. In a diabetic's body that can cause high blood sugar levels. Insulin did not work well at all for me during that 42 hour period. Then my numbers started falling and my normal blood sugar levels appeared. That was so scary!!! I was concerned that I would never have good numbers again. This was my first experiencing this. Here is a quote from my Google research: "Your body naturally makes steroids by itself. When your body is under stress (caused by infection or surgery, for example) it makes extra steroids."
Here is the link: http://familydoctor.org/familydoctor/en/drugs-procedures-devices/prescription-medicines/how-to-stop-steroid-medicines-safely.html