Osteocytes are embedded in the mineralised bone matrix and are connected with each other via a dense network of canaliculi. The osteocyte network is thought to control bone remodelling and to contribute to mineral homeostasis via the process of osteocytic osteolysis. Our investigations focus on how the osteocyte lacuno-canalicular network (OLCN) is orientated, specifically in relation to the concentric lamellae within human osteons. Four samples of cortical bone from femora of middle-aged healthy women were stained with rhodamine allowing to three-dimensionally image the network within 10 osteons in each sample using confocal laser scanning microscopy.1 The image data of the OLCN was skeletonised rendering the network topology. The lamellar structure was obtained using the second harmonic generated (SHG) signal of collagen, which allowed defining dark lamellae (collagen orientation predominantly perpendicular to the image plane) and bright lamellae. Most of the network is oriented radially towards the centre of the osteon. More quantitatively, 64±1% of the canalicular length has an angle smaller than 30o to the direction towards the osteon center, while the lateral network defined by an orientation angle larger than 60o comprises 16±1%. Within dark lamellae most of this lateral network is parallel to the Haversian canal, and the orientation of the canaliculi twists when moving along the direction of bone deposition across a bright and dark lamella. The lateral network can, therefore, be described by a twisted plywood model being coaligned with the orientation of the collagen matrix. However, our data indicate additional structural changes in the network alignment between bright and dark lamellae. The results of our investigation agree with the hypothesis that dendritic cell processes are involved in the alignment of the collagen matrix during osteoid formation.
Disclosure: The authors declared no competing interests.
1. M. Kerschnitzki et al., (2013) JBMR 28 18371845.