Risk Factors for Femoral Head Collapse in Osteonecrosis

Osteonecrosis of the femoral head (ONFH) affects at least 20,000 patients annually in the United States; however, the pathophysiology of disease progression is poorly understood. The purpose of this study was to determine the relative importance of three distinct elements and their relationship to the collapse of the femoral head as follows: (1) identifiable risk factors, (2) femoral head anatomy, and (3) the extent of the necrotic lesion.

A single-center retrospective cohort study was performed on patients ≥ 18 year old who presented with ONFH. Ficat classification and femoral head anatomic parameters were measured on radiographs. Osteonecrotic lesion size was measured on magnetic resonance imaging using four validated methods. Multivariable regression analyses were performed to identify predictors of femoral head collapse.

There were 105 patients and 137 hips included in the final cohort, of which 50 (36.5%) had collapse of the femoral head. Multivariable analyses demonstrated that medical risk factors (adjusted odds ratio (aOR): 1.15), alcohol exposure (aOR: 1.23), and increased alpha angle (aOR: 4.51) were predictive of femoral head collapse. Increased femoral head offset (aOR: 0.54) was protective against collapse. An increased size of the osteonecrotic lesion was significantly predictive of collapse with all four measurement methods evaluated: three-dimensional volumetric (aOR: 3.73), modified Kerboul (aOR: 2.92), index of necrotic extent (aOR: 1.91), and modified index of necrotic extent (aOR: 2.05).

In an analysis of patients who had ONFH, we identified risk factors such as alcohol exposure, high alpha angle, increased lesion size, and decreased femoral offset as increasing the risk of femoral head collapse. Given the challenges of studying this patient population, large prospective studies of patients who have ONFH should seek to identify whether these factors are reliable indicators of femoral head collapse.

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