Periosteum

The periosteum is a thin, highly vascularized connective tissue membrane that covers the outer surface of most bones, except at articular surfaces and sites of tendon or ligament attachment. It consists of two distinct layers: an outer fibrous layer composed primarily of dense irregular connective tissue, and an inner cambium (osteogenic) layer rich in progenitor cells, including mesenchymal stem cells, which are essential for bone growth, repair, and remodeling.

The periosteum serves multiple functions: it provides physical protection to bone, acts as a reservoir for osteogenic and chondrogenic cells, supplies blood to the underlying cortical bone, and participates in the sensing and response to mechanical stimuli.