Classification of osteonecrosis of the femoral head: Who should have surgery?

Abstract

Objectives: Using a simple classification method, we aimed to estimate the collapse rate due to osteonecrosis of the femoral head (ONFH) in order to develop treatment guidelines for joint-preserving surgeries.

Methods: We retrospectively analyzed 505 hips from 310 patients (141 men, 169 women; mean age 45.5 years (sd 14.9; 15 to 86)) diagnosed with ONFH and classified them using the Japanese Investigation Committee (JIC) classification. The JIC system includes four visualized types based on the location and size of osteonecrotic lesions on weightbearing surfaces (types A, B, C1, and C2) and the stage of ONFH. The collapse rate due to ONFH was calculated using Kaplan-Meier survival analysis, with radiological collapse/arthroplasty as endpoints.

Results: Bilateral cases accounted for 390 hips, while unilateral cases accounted for 115. According to the JIC types, 21 hips were type A, 34 were type B, 173 were type C1, and 277 were type C2. At initial diagnosis, 238/505 hips (47.0%) had already collapsed. Further, the cumulative survival rate was analyzed in 212 precollapsed hips, and the two-year and five-year collapse rates were found to be 0% and 0%, 7.9% and 7.9%, 23.2% and 36.6%, and 57.8% and 84.8% for types A, B, C1, and C2, respectively.

Conclusion: Type A ONFH needs no further treatment, but precollapse type C2 ONFH warrants immediate treatment with joint-preserving surgery. Considering the high collapse rate, our study results justify the importance of early diagnosis and intervention in asymptomatic patients with type C2 ONFH.Cite this article: Y. Kuroda, T. Tanaka, T. Miyagawa, T. Kawai, K. Goto, S. Tanaka, S. Matsuda, H. Akiyama. Classification of osteonecrosis of the femoral head: Who should have surgery?. Bone Joint Res 2019;8:451-458. DOI: 10.1302/2046-3758.810.BJR-2019-0022.R1.

Keywords: Collapse; Femoral head; Joint-preserving surgery; Kaplan–Meier survival analysis; Osteonecrosis.

Fig. 1

Schematic representation of T1-weighted MRIs of the 2001 revised Japanese Investigation Committee classification system based on type. The classification schema comprises four types (A, B, C1, and C2). Type A involves the smallest osteonecrotic lesions of the four types (present only in the medial one-third, or less, of the weightbearing surface). Type B involves osteonecrotic lesions present in the medial two-thirds, or less, of the weightbearing surface. Type C1 lesions are characterized by an osteonecrotic zone that spans more than the medial two-thirds of the weightbearing surface at the acetabular edge. Type C2 involves the largest osteonecrotic zone that spans more than the medial two-thirds of the weightbearing surface and exceeds the acetabular edge.

Fig.2

Kaplan–Meier survival curves of precollapse cases. a) The cumulative five-year survival rates indicate that the collapse rate of precollapse osteonecrosis of the femoral head (ONFH) cases is 0% to 84.8%, in the order of smaller to larger lesion sizes. Type C2 progressed quickly, with 37% at one year and 58% at two years reaching the endpoint. b) Collapse rate of precollapse ONFH cases according to sex; there were no differences in terms of time to collapse (p = 0.453, log-rank test). c) Collapse rate of precollapse ONFH cases according to laterality; there were no differences in terms of time to collapse (p = 0.580, log-rank test). d) Collapse rate of precollapse ONFH cases according to steroid use; there were no differences in terms of time to collapse (p = 0.961, log-rank test).

Fig. 3

Five-year collapse rates and hazard ratios (HRs) of each disease type as evaluated by the Cox regression model. A higher collapse rate and an increase in HR for collapse of the femoral head can be seen as the osteonecrotic lesion size increases.