Arm 3: Oral dexamethasone taper (Active Intervention) AND sham injection (Sham Control) Oral dexamethasone taper is a 15 day tapered dosing: (i) days 1-5, dexamethasone 4 mg morning and evening, (ii) days 6-10, dexamethasone 2 mg morning and evening, and (iii) days 11-15, dexamethasone 1mg morning and evening. The dexamethasone gelatine capsule is identical to the placebo capsule in appearance. 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.