Calcified Cartilage Zone Remodeling Induced by IL-1β Derived from Necrotic Subchondral Bone Initiates Cartilage Degeneration in Patients with Glucocorticoids-induced Osteonecrosis of the Femoral Head.

Glucocorticoids-induced osteonecrosis of the femoral head (GONFH) is characterized by progressive cartilage degeneration, yet the role of calcified cartilage zone (CCZ) remodeling in this process remains poorly understood. This study investigated how the inflammatory microenvironment within necrotic subchondral bone drove CCZ remodeling and subsequent cartilage degeneration. Using osteochondral tissues from GONFH patients and interleukin-1β (IL-1β)-treated hypertrophic chondrocytes induced by ATDC5 cells, we combined histology, immunohistochemistry, scanning electron microscopy, energy dispersive spectrometer, transmission electron microscopy, nanoindentation testing, enzyme linked immunosorbent assay and fluorescent tracking to evaluate morphological, biomechanical, and molecular changes. Our findings revealed that CCZ of GONFH exhibited significant thinning, matrix decomposition, demineralization, diminished mechanical strength, and increased porosity. Spatial analysis demonstrated a strong correlation between CCZ remodeling and site-specific cartilage degeneration. Notably, IL-1β was overexpressed in necrotic subchondral bone and the site deep zones of cartilage. It potently enhanced catabolic activity in hypertrophic chondrocytes, promoting matrix metalloproteinase expression while impairing mineralization capacity. This study uncovers a novel pathological cascade in GONFH: necrotic subchondral bone-derived IL-1β drives CCZ remodeling via biomechanical and biological pathways, leading to cartilage degeneration independent of femoral head collapse. Our findings highlight IL-1β as a critical therapeutic target, providing a rationale for subchondral bone-targeted anti-inflammatory strategies to mitigate GONFH progression.