Table 3.

Quality assessment of observational studies using the Newcastle-Ottawa scale

	Wychowansky et al. 2020 [11]	Yuce et al. 2019 [12]	Nord et al. 2019 [23]	Giesenhagen et al. 2019 [20]	Chandra et al. 2019 [10]	Sindel et al. 2018 [27]	Giraddi et al. 2017 [21]	Rizzo et al. 2017 [26]	Flanagan et al. 2016 [17]	Omara et al. 2016 [24]	Fukuda et al. 2005 [18]
Selection
• Representativeness of the exposed cohort	*	*	*	*	*	*	*	*	*	*	*
• Selection of the non-exposed cohort	*	*	*	*	*	*	*	*	*	*	*
• Ascertainment of exposure	*	*	*	*	*	*	*	*	*	*	*
• Demonstration that outcome of interest was not present at start of study	*	*	*	*	*	*	*	*	*	*	*
Comparability
• Study controls for bone ring group	*				*
• Study control for any additional factor (duration of exposure)	*				*
Outcome
• Assessment of outcome	*	*	*	*	*	*	*	*	*	*	*
• Was follow-up long enough for outcomes to occur?	*	*	*	*		*		*	*		*
• Adequacy of follow up of cohorts	*	*	*	*		*		*	*		*
Newcastle-Ottawa scale	9	7	7	7	9	7	5	7	7	5	7