Single-Cell RNA Sequencing Reveals Distinct Cellular and Molecular Features of Steroid-Induced Osteonecrosis of the Femoral Head Compared to Alcohol-Induced Osteonecrosis and Hip Osteoarthritis

Osteonecrosis of the femoral head (ONFH) remains a devastating complication of glucocorticoid therapy and alcohol abuse, yet the pathophysiology is poorly understood. Using single-cell RNA sequencing, we analyzed femoral head specimens from patients undergoing total hip arthroplasty due to steroid-induced ONFH, alcohol-induced ONFH, or hip osteoarthritis (OA). Our comprehensive analysis across conditions revealed etiology-specific cellular compositions and transcriptional profiles. Steroid-induced ONFH demonstrated a distinctive immunological signature characterized by a neutrophil-predominant, elevated innate-to-adaptive immune cell ratio compared to alcohol-induced ONFH or OA. T cell analysis revealed impaired maturation in steroid-induced ONFH, with abundant naïve T cells but reduced mature CD4+ T cells and CD4+ memory T cells compared to both alcohol-induced ONFH and OA. In addition, compared to alcohol-induced ONFH, steroid-induced ONFH was associated with an increase in exhausted/dysfunctional CD8+ T cells which suggests an impaired response to stress and reflects chronic immune dysfunction. Within stromal cell populations, steroid-induced ONFH demonstrated an increase in pericytes, endothelial cells, and mesenchymal cell with osteogenic features as compared to both alcohol-induced ONFH or OA. These findings collectively reveal novel cellular mechanisms underlying steroid-induced ONFH which may contribute to further investigation of etiology-specific pathogenesis and treatment strategies.