Table 2

Risk of Bias assessment of the included trials, according to the criteria by the Cochrane Back and Neck Group [19]

Study authors	1. Was the method of randomization adequate?	2. Was the treatment allocation concealed?	3. Was the patient blinded to the intervention?	4. Was the care provider blinded to the intervention?	5. Was the outcome assessor blinded to the intervention?	6. Was the drop out rate described and acceptable?	7. Were all randomized participants analyzed in the group to which they were allocated?	8. Are reports of the study free of suggestion of selective outcome reporting?	9. Were groups similar at regarding the most important prognostic indicators?	10. Were co-interventions avoided or similar?	11. Was the compliance acceptable in all groups?	12. Was the timing of the outcome assessment similar in all groups?	13. Are other sources of bias unlikely?	Overall risk of bias
Bodes-Pardo et al. [51]	Yes	Unsure	Unsure	No	Unsure	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Unsure
Chaibi et al. [52]	Yes	Yes	No	No	No	No	Yes	Yes	No	Yes	Unsure	Yes	Yes	High
Dunning et al. [53]	Yes	Yes	No	No	No	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Low
Esin et al. [54]	Yes	Unsure	Unsure	No	No	No	Unsure	Yes	Yes	Unsure	Unsure	Yes	Unsure	High
Haas et al. [55]	Yes	Yes	No	No	No	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Low
Haas et al. [56]	Yes	Yes	No	No	No	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Low
Hall et al. [57]	Yes	Unsure	Yes	No	Yes	Yes	Yes	Yes	Yes	No	Unsure	Yes	Yes	High
Jafari et al. [58]	Yes	Unsure	No	No	No	Yes	Yes	Yes	Yes	Yes	Unsure	Yes	Yes	Unsure
Jull et al. [59]	Yes	Unsure	No	No	No	Yes	Yes	Yes	Yes	No	Yes	Yes	Yes	High
Malo-Urriès et al. [60]	Yes	Yes	No	No	No	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Low
Nilsson et al. [61]	Yes	Yes	No	No	No	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Low
Sedighi et al. [62]	Unsure	Unsure	No	No	No	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Unsure
Sharma et al. [63]	Yes	Unsure	No	No	No	Yes	Unsure	Yes	Unsure	Unsure	Unsure	Yes	Unsure	Unsure
von Piekartz et al. 2011 [64]	Yes	Yes	No	No	No	Yes	Yes	Yes	Yes	Unsure	Yes	Yes	Yes	Unsure
Yang and Kang [65]	Unsure	Unsure	No	No	No	No	Unsure	Yes	Unsure	Unsure	Unsure	Yes	Unsure	High
Youssef and Shanb [66]	Yes	Yes	No	No	No	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Low
Abdel et al. [67]	Yes	Yes	No	No	No	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Low
Dunning et al. [68]	Yes	Yes	No	No	No	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Low
Lerner-Lentz et al. [69]	Yes	Yes	No	No	No	Yes	Yes	Yes	Yes	Yes	Yes	Unsure	Yes	Unsure
Moustafa et al. [70]	Yes	Yes	No	No	No	Yes	Yes	No	Yes	Yes	Yes	Yes	Yes	High

Studies were considered as overall low-RoB if no individual domain was rated as “high” or “unsure” RoB. Studies which scored “unsure”, but not “high”, for one or more items, were considered as overall unsure RoB, and “high” if any individual item was rated as high RoB