Multiscale bone quality analysis in osteoarthritic knee joints reveal a role of the mechanosensory osteocyte network in osteophytes

Gustavo Davi Rabelo,Annika vom Scheidt,Michael Amling,Katharina Jähn,Mustafa Citak,Felix Klebig,Björn Busse,Haniyeh Hemmatian

doi:10.1038/s41598-019-57303-z

Gustavo Davi Rabelo, Annika vom Scheidt + Show 6 more

Open Access

https://doi.org/10.1038/s41598-019-57303-z

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Abstract

Osteophytes - bony outgrowths on joint structures - are found in healthy individuals but are specifically present in late osteoarthritis (OA). Osteophyte development and function is not well understood, yet biomechanical stimuli are thought to be critical. Bone adapts to mechanical forces via the cellular network of osteocytes. The involvement of osteocytes in osteophyte formation and maturation has not been unravelled. Forty-three osteophytes from tibias of 23 OA patients (65 ± 9 years) were analysed. The trabecular bone structure of osteophytes presented with fewer trabeculae of lower bone mineral density compared to subchondral bone. We identified 40% early stage and 60% late stage osteophytes that significantly differed in their trabecular bone characteristics. Osteophyte bone revealed a higher number of osteocytes and a lower number of empty osteocyte lacunae per bone area than the subchondral bone. We found that OA osteophytes consist of younger bone material comprised of woven and lamellar bone with the capacity to develop into a late stage osteophyte potentially via the involvement of the osteocyte network. Our analysis of OA osteophytes implies a transition from woven to lamellar bone as in physiological bone growth within a pathological joint. Therefore, osteophyte development and growth present a valuable research subject when aiming to investigate the osteogenic signalling cascade.

Highlights

Osteophytes - bony outgrowths on joint structures - are found in healthy individuals but are present in late osteoarthritis (OA)
Histological analyses enabled the qualitative tissue analysis and quantitative assessment of osteocyte network characteristics. Combining these multi-scale methods, we aim to provide evidence (i) that osteophytes possess a bone composition resembling young bone matrix and arise from an active remodelling process, (ii) that the osteocyte network differs significantly within osteophytes compared to adjacent bone, (iii) that the alterations in tissue composition and osteocyte network characteristics are dependent upon osteophyte maturation, suggesting an adaptive process
The loss of functional cartilage is a hallmark of osteoarthritis and we found that in accordance, the hyaline joint cartilage had been degraded

Summary

Introduction

Osteophytes - bony outgrowths on joint structures - are found in healthy individuals but are present in late osteoarthritis (OA). Changes in the subchondral bone are a hallmark in the progression of OA and bone formation is locally imbalanced leading to the growth of osteophytes[9,10]. In OA, osteophyte formation is of clinical significance: Later stage osteophytes are suggested as a source of pain They may limit joint mobility and contribute to a loss of function, once their growth culminates with limited movement[11]. The question remains if osteophytes develop as a physiological adaptation to changes in mechanical forces or require a pathologically altered joint milieu for their formation. The potential of bone to adapt to mechanical stimuli has been known for decades[21] Osteocytes, with their extensive cellular network, have emerged as bone’s mechanosensory cells[22]. With osteophytes being involved and potentially originating through altered mechanosensation, a functional role of the osteocyte network within these bony spurs would be likely

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