Summary of the experimental interventions by arm
| Arm | Experimental intervention |
| Arm 1 Intervention 1 Injectable dexamethasone and lignocaine OR betamethasone and bupivacaine selective CT fluoroscopy-guided transforaminal lumbar epidural steroid | Drug: betamethasone OR dexamethasone injectable Procedural agents The steroid and local anaesthetic preparation is determined by interventional radiologist’s preferences regarding the use of particulate or non-particulate steroids Dexamethasone 4 mg (1 mL) is a non-particulate corticosteroid and is used with the local anaesthetic lignocaine 1% (1 mL) Betamethasone sodium phosphate/acetate 5.7 mg/mL injectable is a particulate corticosteroid and is used with the local anaesthetic bupivacaine 0.5% (1 mL). Other name: celestone chondrase 5.7 mg/mL injectable suspension Other: oral placebo The oral placebo is a gelatine capsule packed with filler |
| Arm 2 Intervention 2 Normal saline, 0.9% injectable solution with either bupivacaine or lignocaine selective CT fluoroscopy-guided transforaminal lumbar epidural normal saline | Drug: normal saline, 0.9% injectable solution Procedural agents The local anaesthetic preparation used with the normal saline, 0.9% injectable solution will be standardised to replicate current radiology interventional practices: either local anaesthetic bupivacaine 0.5% (1 mL) or local anaesthetic lignocaine 1% (1 mL) Other: oral placebo The oral placebo is a gelatine capsule packed with filler |
| Arm 3 Intervention 3 Dexamethasone oral capsule 15 day tapered dosing as follows: (1) days 1–5, 4 mg morning and evening; (2) days 6–10, 2 mg morning and evening; and (3) days 11–15, 1 mg morning and evening | Drug: dexamethasone oral tablet Dexamethasone oral tablet: 15-day taper dosing is days 1–5, 8 mg (4 mg morning and evening); days 6–10, 4 mg (2 mg morning and evening); and days 11–15, 2 mg (1 mg morning and evening). The dexamethasone is overencapsulated in a gelatine capsule that is identical to the placebo capsule in appearance Other: sham injection The sham injection procedure is needle placement down to muscle at the designated spinal level and no injection of any fluid. |
| Arm 4 Control Sham injection and oral placebo: CT/fluoroscopy-guided (parameters set to zero) transforaminal lumbar sham (needle placement down to muscle and no injection of any fluid) AND placebo oral tablets taper | Sham injection and oral placebo The sham injection procedure is needle placement down to muscle at the designated spinal level and no injection of any fluid. The oral placebo is a gelatine capsule packed with filler |