Fibrillar bone

Because of the spatial organisation of the extracellular bone matrix (EBM), fibrillar bone is distinguished from lamellar bone. The collagen bundles in fibrillar bone are arranged in all directions whereas lamellar bone has a regular structure.

Wherever bone tissue has to be formed very quickly, fibrillar (or primary or immature bone, during development or recovery from a fracture), whereas lamellar (or mature) bone occurs secondarily and requires more time to form. Lamellar bone is formed from spongiform (or canalicular) bone (Spongiosa) and compact bone (Kompakta), which are both lamellar in structure. They are only different in the way in which their fibres are organised. Canalicular bone is made up of flat fibres parallel to its surface whereas a compact bone is made up of concentric fibres arranged around a blood vessel. The lamellar structure can be seen under a polarising microscope.