Hi
@Eyak
I'm so sorry that the prednisone protocol that was used as likely just one of the immunosuppressive medications to prevent rejection after your kidney transplant is the cause of your AVN and that your hip needs replacing ...thankfully bionic hips are really an amazing cure for bad hips.
I know you are nervous, and rightfully so, but regarding your other aches....I know when my hips were at their worst (not due to AVN, just good old end-stage OA) that I was experiencing full body aches, particularly in joint areas (shoulders, ankles, elbows, back) and I attribute to a hyped up immune response along with the bad posture / gait that comes along with bad hips.
Hard not to let our minds wonder...is it just my hips?
I know you are already dealing with one complication caused by your transplant, but please don't let your mind (and/or especially the frightening Dr. Google) while focusing on the symptoms cause you unnecessary stress.
Septic arthritis is an infection caused by either a bacterial or fungal infection, and your OS certainly will be doing bloodwork to check for infection.
A definitive test, even with blood markers that can be inconclusive, can be done by analyzing joint fluid.
Do Iet your OS help alleviate any concerns you have...
But I can tell you that my chronic inflammation and pain research before my hip diagnosis led me (on line) to all matter of horrid diagnoses including bone cancer

A bone scan showed this was thankfully not the case.
I hope all your concerns can be addressed so that you can go into surgery in a better place.
Hugs!