Table 2.

Common characteristics about studies included in the systematic review

Source	Country	Published year	Study design	Disease	No. of patients			No. of levels (mean)
					A	P	Total	A	P
Kristof et al. [28]	Germany	2009	NRCT	CSM	42	61	103	2	3
Bapat et al. [30]	India	2008	NRCT	CSM	20	25	45	3.0	3.2
Edwards et al. [34]	USA	2001	Cohort	CM	13	13	26	≥3	≥3
Wada et al. [35]	Japan	2001	NRCT	CSM	23	24	47	2.3	2.5
Yonenobu et al. [37]	Japan	1992	NRCT	CSM	41	42	83	2.5	2.6
Lee et al. [29]	South Korea	2008	NRCT	OPLL	20	27	47	3.4	5.5
Iwasaki et al. [31]	Japan	2007	NRCT	OPLL	27	66	93	3.0	5.7
Jain et al. [32]	India	2005	NRCT	OPLL	14	13	27	≥4	≥4
Tani et al. [33]	Japan	2002	NRCT	OPLL	14	12	26	3.2	5.6
Goto and Gita [36]	Japan	1995	NRCT	OPLL	7	57	64	≥3	≥3

NRCT non-randomized controlled clinical trial, OPLL multilevel cervical ossification of the posterior longitudinal ligament, CSM multilevel cervical spondylotic myelopathy, MCM multilevel cervical myelopathy, No. number