3D morphometric analysis of calcified cartilage properties using micro-computed tomography

Our aim is to establish methods for quantifying morphometric properties of calcified cartilage (CC) from micro-computed tomography (microCT). Furthermore, we evaluated the feasibility of these methods in investigating relationships between osteoarthritis (OA), tidemark surface morphology and open subchondral channels (OSCCs).

Samples (n = 15) used in this study were harvested from human lateral tibial plateau (n = 8). Conventional roughness and parameters assessing local 3-dimensional (3D) surface variations were used to quantify the surface morphology of the CC. Subchondral channel properties (percentage, density, size) were also calculated. As a reference, histological sections were evaluated using Histopathological osteoarthritis grading (OARSI) and thickness of CC and subchondral bone (SCB) was quantified.

OARSI grade correlated with a decrease in local 3D variations of the tidemark surface (amount of different surface patterns (r_s = -0.600, P = 0.018), entropy of patterns (EP) (r_s = -0.648, P = 0.018), homogeneity index (HI) (r_s = 0.555, P = 0.032)) and tidemark roughness (TMR) (r_s = -0.579, P = 0.024). Amount of different patterns (ADP) and EP associated with channel area fraction (CAF) (r_p = 0.876, P < 0.0001; r_p = 0.665, P = 0.007, respectively) and channel density (CD) (r_p = 0.680, P = 0.011; r_p = 0.582, P = 0.023, respectively). TMR was associated with CAF (r_p = 0.926, P < 0.0001) and average channel size (r_p = 0.574, P = 0.025). CC topography differed statistically significantly in early OA vs healthy samples.

We introduced a micro-CT image method to quantify 3D CC topography and perforations through CC. CC topography was associated with OARSI grade and OSCC properties; this suggests that the established methods can detect topographical changes in tidemark and CC perforations associated with OA.