Data open access: Published data will be available at www.figshare.com. Statistical analysis Statistical analysis will be performed by a professional statistician (blinded to grouping) using SPSS 19.0 software. If Runx2, BMP-2, BMP-7 and osteoprotegerin mRNA expression, as well as osteocalcin immunoreactivity in the femoral head and neck of patients with ONFH and osteoarthritis, are normally distributed, a two-sample t-test will be used to compare differences between groups. If, however, these data are not normally distributed, a Mann-Whitney U test will be used. A level of P < 0.05 will be considered statistically significant.