In addition to osteoblasts and osteoclasts, bone tissue – whether cortical or trabecular – contains numerous osteocytes that arise from osteoblasts and are thus of mesenchymal origin (Bonewald, 2011). While osteoblasts and osteoclasts are considered responsible for bone formation and resorption in bone remodeling, osteocytes were viewed for a long time as an inactive cellular entity within the bone (Tresguerres et al., 2020). However, osteocytes account for 85–90% of all cells in bone tissue (Wang et al., 2022). Recent investigations have shown that bone is able to adjust its structure to mechanical signals through remodeling processes regulated by mechanosensitive osteocytes (Hemmatian et al., 2017).

The ability of osteocytes to sense and respond to mechanical stimuli depends on many factors, such as the shape of the osteocyte cell bodies, numbers and length of the cell processes, structure of the cytoskeleton, and presence of primary cilia (Hemmatian et al., 2017).

On the one hand, osteocytes regulate the activity and recruitment of osteoblasts and/or osteoclasts by producing a large number of signaling molecules (PGE 2, NO, COX-2, FGF-23, RANKL/OPG, sclerostin) (Klein-Nulend et al., 2013). On the other hand, osteocytes are prone to apoptosis, which is followed by bone resorption in the affected area after estrogen deprivation (Tomkinson et al., 1998), glucocorticoid excess (Weinstein et al., 1998), and fatigue-induced microdamage (Verborgt et al., 2000).

In general, bone mass is determined by the metabolic activity of osteoblasts and osteoclasts, whereas the local bone architecture results from local recruitment of osteoblasts and/or osteoclasts through osteocytes (Klein-Nulend et al., 2015). With advancing age, the imbalance in bone remodeling causes osteoporosis (OP). Bone atrophy in women is expressed as a loss of trabecular number, while men reveal a general rarefaction of trabecular architecture with advancing age (Bergot et al., 1988, Aaron et al., 1987, Mosekilde, 1989).

In the presence of OP, the reduction of bone mass, structure and function may cause a fracture even in the presence of low-energy trauma (Chadha et al., 2022). Fractures in OP occur independent of age and gender, primarily in the distal radius, the proximal femur and the spine (Hadji et al., 2013). Vertebral body fractures are associated with health and economic burdens, increase morbidity and mortality, and impair quality of life (Oleksik et al., 2000).

Since local changes may be related to the reactivity of osteocytes, the number of osteocytes in the various portions of the spine is worthy of investigation. Structural differences develop between the cervical spine (CS), the thoracic spine (TS), and the lumbar spine (LS) (Schröder et al., 2021b, Schröder et al., 2021a, Grote et al., 1995), resulting in various levels of fracture risk. To our knowledge, the number of osteocytes in the three sections of the human spine have not been investigated so far. In the current study, we aimed to answer the following questions:

Question 1

Do osteocyte density, trabecular structure, and bone area differ between the cervical, thoracic and lumbar spine?

Question 2

Do the individual parameters correlate with each other?

Question 3

Do osteocyte density, trabecular structure and bone area differ between men and women?

Question 4

Do osteocyte density, trabecular structure and bone area differ between older and young individuals?