What Causes Electric Shock Sensation From Legs To Feet After Having Cortisone?

Hi I had cortisone injections to my lower spine in January and I ve been suffering with what I can describe as electrical currants down both legs to my feet, although I ve had these injections many times before I ve never experienced this also we needle went into my spine I got an almighty pain in the middle of my shoulders what has happened this time and why?