Fig. 2From: Comparison of cervical disc arthroplasty and anterior cervical discectomy and fusion for the treatment of cervical disc degenerative diseases on the basis of more than 60 months of follow-up: a systematic review and meta-analysisAssessment of risk of bias for RCT: “+”: low risk of bias; “−”: high risk of bias; “?”: unclear risk of biasBack to article page