Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Randomly allocated
Allocation concealment (selection bias)	Unclear risk	Not reported
Blinding of participants and personnel (performance bias)	High risk	Unlikely
Blinding of outcome assessment (detection bias)	Unclear risk	Not reported
Incomplete outcome data (attrition bias)	Low risk	Data provided for all participants
Selective reporting (reporting bias)	High risk	Eight failed spinal converted to GA, not in intention‐to‐treat
Other bias	Low risk	Group well balanced for age, delayed injury‐surgery and incidence of major systemic disease.