Developmental Transformation and Reduction of Connective Cavities within the Subchondral Bone.

Shahed Taheri,Sebastian Baumbach,Lia Schenk,Thomas Winkler,Arndt Schilling,Wolfgang Lehmann,Jozef Zustin,Carl Neuerburg

doi:10.3390/ijms20030770

Abstract

It is widely accepted that the subchondral bone (SCB) plays a crucial role in the physiopathology of osteoarthritis (OA), although its contribution is still debated. Much of the pre-clinical research on the role of SCB is concentrated on comparative evaluations of healthy vs. early OA or early OA vs. advanced OA cases, while neglecting how pure maturation could change the SCB’s microstructure. To assess the transformations of the healthy SCB from young age to early adulthood, we examined the microstructure and material composition of the medial condyle of the femur in calves (three months) and cattle (18 months) for the calcified cartilage (CC) and the subchondral bone plate (SCBP). The entire subchondral zone (SCZ) was significantly thicker in cattle compared to calves, although the proportion of the CC and SCBP thicknesses were relatively constant. The trabecular number (Tb.N.) and the connectivity density (Conn.D) were significantly higher in the deeper region of the SCZ, while the bone volume fraction (BV/TV), and the degree of anisotropy (DA) were more affected by age rather than the region. The mineralization increased within the first 250 µm of the SCZ irrespective of sample type, and became stable thereafter. Cattle exhibited higher mineralization than calves at all depths, with a mean Ca/P ratio of 1.59 and 1.64 for calves and cattle, respectively. Collectively, these results indicate that the SCZ is highly dynamic at early age, and CC is the most dynamic layer of the SCZ.

Highlights

Osteoarthritis (OA) is a degenerative joint disease with several verified risk factors including sex, immobility, obesity, and joint injuries [1]
The thickness of the calcified cartilage (CC) was 168.6 μm ± 63.7 μm, which accounts to 34.1% of the subchondral zone (SCZ)
Calves demonstrated a fine trabecular structure, large co-continuous trabecular cavities, and small conduits within the CC, whereas cattle were characterized by thicker trabeculae, a more compact bone structure, and only a few conduits in the CC region

Summary

Introduction

Osteoarthritis (OA) is a degenerative joint disease with several verified risk factors including sex, immobility, obesity, and joint injuries [1]. Other common causes include inappropriate mechanical stress to the joint via malposition of the axis, mechanical overload, or inflammatory joint processes [2]. The strongest risk factor for OA is age. The age of 30, OA is virtually absent [3], suggesting a change in joint physiology after young adulthood that enables. This change could directly affect cartilage [4]. Cartilage degradation can trigger a vicious circle that eventually leads to the destruction of the joint [5]

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Discussion

Conclusion