Large-area time-of-flight secondary ion mass spectrometry (ToF-SIMS) imaging of the human growth plate from polydactyly specimen

Abstract

The spatial organization of organic/inorganic components at the cartilage–bone interface in the human growth plate remains poorly understood. This study uses time-of-flight secondary ion mass spectrometry (ToF-SIMS) for the first time on human growth plate samples to provide insights into these interfaces. Three polydactyly specimens were analysed to map spatial variations of hydroxyapatite and collagen-related components. Regions of interest were statistically evaluated using Dunn’s multiple comparisons and Spearman correlations. The calcified cartilage interface represents a critical transition zone, marked by a sharp decline in organic matrix components (e.g. CH₄N⁺) and a concurrent increase in mineral fragments (CaPO₂⁺, Ca⁺), particularly evident in large-area images. A significant peak in the Ca⁺/CH₄N⁺ ratio (p < 0.0001) highlighted a rapid shift from organic-rich to mineral-rich composition. Correlations between organic (CNO⁻) and mineral (PO₂⁻) markers indicated early-stage mineralization, while phosphate and mineralized bone fragments confirmed full mineralization (trabecular and cortical bone). Results were consistent with existing literature, supporting a structured, progressive mineralization pattern characteristic of endochondral ossification. This study demonstrates the first application of ToF-SIMS on human growth plate samples from polydactyly cases, highlighting the capacity of ToF-SIMS for large-scale imaging of human growth plate interfaces and its potential relevance to orthopaedic research.