Effect of femoral head necrosis cystic area on femoral head collapse and stress distribution in femoral head: A clinical and finite element study

The purpose of this study was to investigate the effect of cystic areas of osteonecrosis of the femoral head (ONFH) on stress distribution and disease progression in the femoral head. A total of 85 patients (106 hips) diagnosed with Association Research Circulation Osseous stage II non-traumatic and non-surgical treatment were retrospectively analyzed. The presence of cystic areas and diameter of cystic areas were compared between the two groups. In addition, five spherical cystic areas of different diameters were constructed and the maximum stress was observed. There was a difference between the two groups in whether cystic areas appeared in the femoral head, with 49.1% in the collapse group showing cystic areas, which was significantly higher than that in the non-collapse group (18.4%) (P < 0.05). In addition, the diameter of the cystic areas was significantly larger in the collapsed group than in the non-collapsed group (P < 0.05). The maximum and mean von Mises stress value around the necrotic area and around the cystic area of the femoral head increased with the increase of the cystic diameter. Stress concentration areas can be generated around the cystic areas. The presence and increased diameter of the cystic areas accelerates the collapse of the ONFH femoral head.