Arm 4: Sham injection (Sham Control) AND oral placebo taper (Placebo Control) The sham injection is CT/fluoroscopic guided (with parameters set to zero) lumbar sham injection. The needle placement is down to muscle layer but NOT into the epidural space, and there is no injection of any fluid. The oral placebo is a gelatine capsule with filler. It is identical to the dexamethasone capsule in appearance.