Value of CT in quantitatively diagnosing and assessing collapse in patients with femoral head necrosis based on finite element mechanics analysis

BACKGROUND: Mechanical analysis of the femoral head is mostly conducted through finite element analysis (FEA), the operation of which is relatively complex. In this study, the correlation between computed tomography (CT) quantitative analysis and FEA in the diagnosis of osteonecrosis of the femoral head (ONFH) was analyzed. METHODS: This retrospective study involved 30 hips from patients with Steinberg stage II ONFH who had not received treatment. The average CT density was measured, and an FEA model was constructed on the basis of the CT images of each case. The correlation between the average CT density and the FEA measurements was analyzed. RESULTS: The average CT density of the coronal midline plane was 370.47 ± 16.85 HU, and that of the maximum necrotic layer was 420.73 ± 22.24 HU. According to the FEA results, the maximum total displacement was 0.42 ± 0.04 mm, the maximum displacement in the Z direction was 0.25 ± 0.02 mm, the maximum equivalent stress in the stress concentration zone of the head was 1.81 ± 0.02 MPa, and the failure coefficient was 0.34 ± 0.02. The average CT density of the maximum necrotic layer was not correlated with the maximum total displacement or maximum displacement in the Z direction but was correlated with the maximum equivalent stress (r = 0.65; P < 0.1001) and failure coefficient (r=-0.58; P < 0.001). The average CT intensity of the maximum slice (P = 0.004) and the average failure coefficient (P = 0.020) significantly differed between the collapse and noncollapse groups. CONCLUSION: CT quantification can reflect the load distribution and bearing capacity of ONFH to some extent. The higher the average CT density of the maximum slice, the lower are the average failure coefficient of the femoral head and the clinical risk of collapse.