Novel CT based 2021 ARCO Classification for Osteonecrosis of the Femoral Head

The Association Research Circulation Osseous(ARCO) has developed a novel classification for early stage (precollapse) osteonecrosis of the femoral head (ONFH).Kyung-Hoi Koo & Michael A. Mont et al. hypothesized that the novel classification is more reliable and valid when compared to previous 3 classifications: Steinberg, modified Kerboul, and Japanese Investigation Committee (JIC) classifications.

In the novel classification, necrotic lesions were classified into 3 types:

• Type 1 is a small lesion, where the lateral necrotic margin is medial to the femoral head apex;

• Type 2 is a medium-sized lesion, with the lateral necrotic margin being between the femoral head apex and the lateral acetabular edge; and

• Type 3 is a large lesion, which extends outside the lateral acetabular edge.

In a derivation cohort of 40 early-stage osteonecrotic hips based on computed tomography imaging, reliabilities were evaluated using kappa coefficients, and validities to predict future femoral head collapse by chi-squared tests and receiver operating characteristic curve analyses. The predictability for future collapse was also evaluated in a validation cohort of 104 early-stage ONFH.

In the derivation cohort, interobserver reliability (k = 0.545) and intraobserver agreement (63%- 100%) of the novel method were higher than the other 3 classifications.

The novel classification system was best able to predict future collapse (P <.05) and had the best discrimination between nonprogressors and progressors in both the derivation cohort (area under the curve = 0.692 [0.522- 0.863], P < .05) and the validation cohort (area under the curve = 0.742 [0.644-0.841], P = 2.46 x 10-15).

The authors concluded that – the 2021 ARCO classification for early stages of ONFH is more reliable and valid than Steinberg, modified Kerboul, and JIC classifications. ARCO recommends using this novel method for the categorization of early-stage ONFH. Future validating studies involving larger and different patient cohorts are warranted.

Further reading:

The 2021 Association Research Circulation Osseous Classification for Early-Stage Osteonecrosis of the Femoral Head to Computed Tomography Based Study

Kyung-Hoi Koo & Michael A. Mont et al

The Journal of Arthroplasty 37 (2022) 1074-082

https://doi.org/10.1016/j.arth.2022.02.009.