Characterization of calcifications in posterior horn of human meniscus using micro-computed tomography

Objective Meniscal calcifications are associated with meniscal degeneration and osteoarthritis (OA). We investigated micro-computed tomography (µCT) imaging for identification of calcification patterns caused by basic calcium phosphate (BCP) and calcium pyrophosphate (CPP). Design Posterior horns of human medial and lateral menisci from 19 individuals with medial compartment knee OA and 21 deceased donors were imaged with high-resolution µCT. Raman spectroscopy characterized the calcification types from histological sections, adjacent to µCT piece. Qualitative and quantitative analysis, visualization, and grading were performed using 3D µCT images of meniscal calcifications.

Different calcification patterns were observed with BCP and CPP. BCP was found at the borders of meniscal tissue and inside complex tears or fibrillation. In contrast, CPP accumulated as circumferential rod-like structures between collagen bundles, mainly inside the meniscal tissue, and lacked the porous 3D structure observed in BCP calcifications. Quantitatively, CPP samples had a higher calcification volume compared to BCP with a geometric mean ratio of 14 (95%CI; 3,73), and larger particle sizes with a ratio of 7 (95%CI; 2,8). Additionally, BCP calcifications had an organized porous structure with a closed porosity range of 6–19, while a similar structure was not seen in CPPs (range 1–3.5).

We qualitatively and quantitatively identified volumetric and morphological differences in the calcification deposition patterns between BCP and CPP calcifications in human meniscus. The calculated differences may help distinguish the calcification types with in vivo imaging modalities in the future, as well as provide a better understanding of their role in OA. Competing Interest Statement ME reports past consultancy for Grunenthal Sweden AB, Key2Compliance AB and Genascence. The other authors report no conflicts of interest.