Table 2.

Criteria for risk of bias assessment

	Question	Criteria	Judgment
1	Was the method of randomization adequate?	A random (unpredictable) assignment sequence. Adequate methods including computer-generated random sequence, coin toss, rolling a dice, drawing of ballots with the study group labels from a dark bag, preordered sealed envelops, and sequentially ordered vials.	Yes/No/Unsure
2	Was the treatment allocation concealed?	Adequate if the allocation of patients involved a central independent unit, on-site locked computer, identically appearing numbered drug bottles or containers prepared by an independent pharmacist or investigator, or sealed envelopes.	Yes/No/Unsure
3	Was the patient blinded to the intervention?	The index and fusion groups are indistinguishable for the patients.	Yes/No/Unsure
4	Was the care provider blinded to the intervention?	The index and fusion groups are indistinguishable for the care providers.	Yes/No/Unsure
5	Was the outcome assessor blinded to the intervention?	For patient-reported outcomes with adequately blinded patients for outcome criteria that supposes a contact between participants and outcome assessors: the blinding procedure is adequate if patients are blinded, and the treatment or adverse effects of the treatment cannot be noticed during examination for outcome criteria that do not suppose a contact with participants: the blinding procedure is adequate if the treatment or adverse effects of the treatment cannot be noticed during the assessment for outcome criteria that are clinical or therapeutic events that will be determined by the interaction between patients and care providers, in which the care provider is the outcome assessor: the report needs to be free of selective outcome reporting.	Yes/No/Unsure
6	Was the dropout rate described and acceptable?	The number of participants who were included in the study but did not complete the observation period or were not included in the analysis are described and reasons are given and are <20 % or short-term and <30 % for long-term follow-up.	Yes/No/Unsure
7	Were all randomized participants analyses in the group to which they were allocated?	All randomized patients are reported/analyzed in the group they were allocated to by randomization for the most important moments of effect measurement (minus missing values) irrespective of noncompliance and cointerventions.	Yes/No/Unsure
8	Are reports of the study free of suggestion of selective outcome reporting?	In general, we expected studies comparing interventions for low back pain to assess at least pain, Oswestry (or similar) scores and to evaluate mobility/fusion of the motion segment. If there were too many studies without these parameters, reporting bias was suspected, unless confirmed by a full protocol.	Yes/No/Unsure
9	Were the groups similar at baseline regarding the most important prognostic indicators?	The groups have to be similar at baseline regarding demographic factors, duration, and severity of complaints, percentage of patients with neurological symptoms, and value of main outcome measure(s).	Yes/No/Unsure
10	Were co-interventions avoided or similar?	There were no cointerventions or they were similar between the index and fusion groups.	Yes/No/Unsure
11	Was compliance acceptable in all groups?	The compliance with the interventions based on the reported intensity, duration, number, and frequency of sessions for both the index intervention and fusion intervention.	Yes/No/Unsure
12	Was the timing of the outcome assessment similar in all groups?	Timing of outcome assessment was identical for all intervention groups and for all important outcome assessments.	Yes/No/Unsure