Table 2. Quality assessment of included studies according to NOS.

Study	Selection	Comparability	Outcome/exposure	Total score
George et al. [2018]	****	*	*	6
Smith et al. [2018]	****	*	**	7
Shohat et al. [2018]	****	*	**	7
Jung et al. [2017]	****	*	**	7
Lübbeke et al. [2016]	****	*	**	7
Bohl et al. [2016]	****	*	*	6
Tornero et al. [2015]	****	*	**	7
Wu et al. [2014]	****	**	*	7
Wallace et al. [2014]	****	*	**	7
Namba et al. [2012]	****	*	***	8
Grant et al. [2008]	****	*	**	7

Each asterisk (*) indicates 1 score. NOS, Newcastle-Ottawa Scale.