The survival of non-traumatic osteonecrosis of femoral head at ARCO II with ring-shaped sclerotic zone: a mid-term follow-up retrospective study

The sclerotic zone in the osteonecrosis of femoral head (ONFH), containing condensed trabecular bone and abundant neovascularization, is the transition area between osteonecrosis and normal tissue. Due to the prominent feature in ONFH, the characteristics of the sclerotic zone might indicate the femoral head survival of the disease. Thirty ONFH patients (41 hips) with ring-shaped sclerotic zone at Association Research Circulation Osseous-II were recruited during 1996 to 2019, and the corresponding radiographic images in their follow-up are reviewed retrospectively. Two subtypes (type A and B) are defined to discriminate different locations of ring-shaped sclerotic zone in the femoral head (center or subchondral bone plate) in accordance with the radiographic images. The natural history of the enrolled subjects was followed up for average 9 years to record and compare their collapse incidences as well as the progress of hip symptoms. Chi-square test shows that the occurrence rates of symptomatic hip of type A are significantly lower than that of type B and differences between these two groups were significant (P < 0.05). Kaplan Meier survival curve analysis shows that the mean survival time of type A is 247.600 M (95% CI: 203.072 ∼ 292.128 M) and type B is 88.795 M (95% CI: 72.607 ∼ 104.984 M). The survival rate of femoral head of type A is significantly higher than that of type B (P < 0.005). This study demonstrates that type A shows a more satisfactory clinical outcomes and lower femoral head collapse rate in a mid-term follow-up.