Understanding the Structure of Trabecular Excrescences Found in Osteoarthritic and Non-Osteoarthritic Joint Samples

Taylor, Adam and Allison, Kathryn and Rhodes, Bryan and Kerns, Jemma and Shepherd, Rebecca (2020) Understanding the Structure of Trabecular Excrescences Found in Osteoarthritic and Non-Osteoarthritic Joint Samples. FASEB Journal, 34 (S1). ISSN 0892-6638

Abstract

The presence of novel bone structures, termed trabecular excrescences, have previously been found in surgical waste tissue samples from patients with osteoarthritis, alkaptonuria and from aged bone samples. A form of trabecular excrescence is found associated with the presence of bone marrow adipocytes and the absence of bone lining cells. We hypothesize that the adipocytes are contributing to the formation of bone like structures. This is inconsistent with the current paradigm of osteoclast-osteoblast coupled remodelling. This study aimed to determine the topographical distribution of trabecular excrescences throughout the trabecular bone in human joint samples and to further characterise their internal structure. Joint samples were obtained as surgical waste, with informed patient consent, from 20 patients with OA (mean age = 75.3) and 20 control patients without OA (mean age = 78.5). North of Scotland NHS Research Ethics Committee (UK) approved this research. Joint samples obtained included femoral heads, humeral heads, ankles, knees and shaft of femur. Each joint sample was sliced into sagittal sections. The sections were decalcified and processed for histology. Unstained sections were viewed under fluorescence microscopy. Sections were stained with haematoxylin and eosin and with immunohistochemical staining for collagen I, collagen VI and osteocalcin. Excrescences were found in both control and osteoarthritic samples. When found, the excrescences were often clustered, with several protrusions shown along a region of trabeculae. These results demonstrate that trabecular excrescences are globally distributed throughout the femoral head, and not specific to areas of osteoarthritic change. This suggests the formation of these structures may be linked to the ageing process rather than disease progression. Immunohistochemical staining demonstrated the presence of collagen VI within the extracellular matrix of the newly formed excrescences. However, we also noted the presence of osteocalcin in ‘smoothed over’ versions of excrescences. This study has shown that trabecular excrescences are initially formed by the deposition of collagen VI by adipocytes. However, the presence of osteocalcin suggested that excrescences have the potential to be remodelled through typical osteoblast-osteoclast remodelling. Future treatments for skeletal disorders could look to exploit the scaffold like properties of structures formed by adipocytes.