Table 1.

Demographic and Baseline Characteristics of the Included Studies.

First Author	Year	Country	Study Design	Number of Patients	Mean Age (Years)	Male/Female	1 Level ACDF	2 Levels ACDF
Hacker RJ et al 6	2000	USA	Prospective	488	44 ± 9/47 ± 7∞	95/84	390	98
					43 ± 8/47 ± 7∞	80/87
					44 ± 9/48 ± 8∞	74/68
Agrillo U et al 7	2002	Italy	Retrospective	45	49.7	26/19	33	12
Cauthen JC et al 8	2003	USA	Retrospective	88	49.5 (34.4-66.1)	15/15	43	45
					51.1 (32.9-67.4)	12/20
					51.4 (29.6-70.3)	13/13
Cosar M et al 9	2008	Turkey	Retrospective	17	46 (33-60)	8/9	17	—
Akula M et al 10	2008	UK	Retrospective	50	51 (31-90)	31/19	42	8
Moon HJ et al 11	2010	South Korea	Retrospective	27	50.8 (31-67)	18/9	—	27
Niu CC et al 12	2010	Taiwan	Retrospective	53	49.5 ± 11.5	15/13	35	18
					52.2 ± 10.5	12/13
Zagra A et al 13	2013	Italy	Retrospective	86	32-60	13/11	80	6
					28-29	15/14
					29-63	17/16
Kim CH et al 14	2013	South Korea	Prospective	52	49.5 ± 12.8	17/12	52	—
					55.2 ± 12.4	14/9
Shin JS et al 15	2014	Korea	Retrospective	60	50.0 ± 12.0	7/13	60	—
					49.0 ± 11.0	12/8
					44.3 ± 9.7	13/7
Kim SJ et al 16	2014	Korea	Retrospective	96	51.9 ± 13.5	25/23	96	—
					46.5 ± 10.5	24/24
Xie Y et al 17	2015	China	Prospective	68	54.6 ± 12.7	20/15	29	39
					56.3 ± 10.5	16/17
Yi J et al 18	2015	Korea	Prospective	77	51.9 ± 11.7	25/13	77	—
					51.3 ± 12.4	26/13
Chin K et al 19	2017	United States	Retrospective	145	53 ± 1.0	33/42	NR	NR
					53.4 ± 1.6	34/36
Farrokhi MR et al 20	2017	Iran	Prospective	64	47.6	12/20	64	—
					45.3	14/18
Yu J et al 21	2017	Korea	Retrospective	247	53.7 ± 10.2	43/33	115	132
					53.8 ± 10.9	46/36
					51.7 ± 9.9	65/24
Shiban E et al 22	2018	Germany	Retrospective	194	54	91/103	98	96

∞ denotes 1-level/2-level.

ACDF – Anterior Cervical Discectomy and Fusion.