Table 1.

Ranking of studies based on their methodological quality according to the GRADE Statement [17]

Domains of GRADE →	Study design	Study quality						Directness		Consistency
Study	Was it a cohort study?	Did the study directly compare the relationship of ON and osteonecrosis?	Was radiographic followup at least 4 years in all included cases?	Was loss-to-followup less than 20%?	Were outcomes ascertained blinded to outcome?	Were multivariate analyses performed?	Was a risk ratio with confidence intervals reported?	Were all conclusions about the relationship between ON and osteonecrosis supported by data?	Were participants, interventions and outcome measures similar to those of interest in clinical practice?	Were estimates of effect (results) similar to other studies?
Roposch et al. (2011) [8]	✓	✓	✓	✓	✓	✓	✓	✓	✓	✓
Sllamniku et al. (2013) [14]	✓	✓	✓	✓	✘	✘	✓	✓	✓	✓
Sibinski et al. (2009) [16]	✓	✓	✓	✓	✘	✘	✘	✓	✓	✓
Pospischill et al. (2011)	✓	✘	✓	✘	✘	✓	✓	✓	✓	✓
Madhu et al. (2013) [19]	✓	✘	✘	✓	✓	✘	✘	✓	✓	✓
Luhmann et al. (1998) [7]	✓	✓	✘	✓	✘	✘	✘	✓	✓	✓
Segal et al. (1999) [3]	✘	✓	✘	✓	✘	✓	✓	✓	✓	✘
Clarke et al. (2005) [2]	✓	✓	✘	✓	✘	✘	✘	✓	✓	✘
Carney et al. (2004) [1]	✓	✓	✘	✓	✘	✘	✘	✓	✓	✘
Cooke et al. (2010) [20]	✘	✓	✓	✓	✘	✘	✘	✘	✓	✘
Agus et al. (2002) [12]	✘	✘	✘	✓	✘	✘	✘	✓	✓	✓
Konigsberg et al. (2003) [6]	✓	✘	✘	✓	✘	✘	✘	✘	✓	✓
Tarassoli et al.(2014) [4]	✓	✘	✘	✓	✘	✘	✘	✘	✓	✘
Zamzam et al. (2009) [5]	✓	✘	✘	✓	✘	✘	✘	✘	✓	✘