Comparison of the 2021 Association Research Circulation Osseous Classification System for Osteonecrosis of the Femoral Head and the Japanese Investigation Committee Classification System.

BACKGROUND

The size and location of the necrotic area are important factors in predicting prognosis and determining treatment in patients who have osteonecrosis of the femoral head (ONFH). This study assessed the utility of the 2021 Association Research Circulation Osseous (ARCO) classification system, which is based on coronal section computed tomography images of the center of the femoral head, by using magnetic resonance imaging (MRI) to classify types of the natural course in non-collapsed ONFH.

METHODS

This research included 102 hips with non-collapse ONFH. There were 40 men and 62 women (mean age 45 years). The patients were followed up for > 2 years (mean 13). The location of the necrotic lesion was categorized according to the 2021 ARCO classification by using MRI and the Japanese Investigation Committee classification. The cumulative survival rate with collapse as the endpoint was evaluated.

RESULTS

According to the 2021 ARCO classification, 27, 42, and 33 hips were classified as types 1, 2, and 3, respectively. The survival rates with collapse as the endpoint were 95% for type 1, 48% for type 2, and 18% for type 3. The collapse rates significantly differed among types 1, 2, and 3 (P < 0.01). Meanwhile, 19 hips were classified as type A, 19 hips as type B, 31 hips as type C1, and 33 hips as type C2 based on the Japanese Investigation Committee classification. The survival rates with collapse as the endpoint were 100, 84, 28, and 13% for types A, B, C1, and C2, respectively. The collapse rates differed significantly between types A and C1, types A and C2, types B and C1, types B and C2, and types C1 and C2 (P < 0.01).

CONCLUSIONS

The 2021 ARCO classification system, by using MRI, is a reliable and valid tool for predicting the occurrence of collapse in patients who have early-stage ONFH.