Table 1. Detailed inclusion and exclusion criteria.

Eligibility	Population	Intervention	Control	Outcome	Study design
Inclusion	Adult patients (≥16 years)	CDA (any device)	ACDF	Index- or adjacent-level reoperations at fixed follow-up time periods (e.g., 2 years)	Multi-center
	One- or two-level cervical spondylosis		Allograft or cage	Minimum follow-up of 1 year	Randomized controlled trial
	Symptomatic with refractory radiculopathy or progressive myelopathy		Anterior plate	For mixed populations, outcomes reported separately for one- and two-level subgroups	English-language publication as a full-text report
Exclusion	Cervical spondylosis affecting more than two levels		Anterior cervical discectomy without fusion	Variable follow-up time periods (e.g., mean follow-up, 3 years; range, 1–5 years)	Single-center
	Cervical spondylosis at non-contiguous levels		Lack of anterior plate fixation (e.g., stand-alone cage)	Failure to distinguish between index- and adjacent-level reoperations	Non-randomized
			Autologous iliac crest bone graft	For mixed populations, lack of stratification of outcomes by one- or two-level cervical spondylosis	Use of historical controls
					Conference abstract
					Non-English language publication

CDA, cervical disc arthroplasty; ACDF, anterior cervical discectomy and fusion.