Endosteum is a thin layer of connective tissue that lines the inner surfaces of all bones (the cavities within the bone).
- Appositional bone growth (in width). Here is a video that shows how endosteum contributes to the growth of the osteons in the cortical bone.
- Bone remodeling: Endosteum stimulates bone resorption on the inner bone surfaces and periosteum stimulates formation of the new bone on the outer bone surfaces — this way the diameter of the medullary canal and the bone as a whole increases with age 11.
- Bone repair after a bone fracture (hematoma > endosteal proliferation > callus formation > consolidation > remodeling) 14
- References: 1,2,9,11
Endosteum is found on all internal surfaces of bones: the medullary cavity, the hollow spaces in the trabecular (spongy) bone, Haversian (osteonic) and Volkmann’s (perforating) canals in the cortical (compact) bone of the long bones, such as humerus and femur, flat bones, such as ribs 5 and pelvic bones 6,8, and sesamoid bones, such as patella 10. NOTE: The surface of the skull bones that faces the brain is not covered by endosteum, but periosteum, which is a part of dura mater. Endosteum covers the cavities within the skull bones, though.
Picture 1. Endosteum location
Endosteum covers all inner surfaces of the bone:
medullary cavity, cavities in the spongy bone and Volkmann’s and Haversian canals
(free image use)
Endosteum Composition, Blood Supply and Innervation
- A single layer of epithelial cells, and osteoprogenitor cells or bone stem cells and cells that develop from them: osteoblasts (bone-forming cells) and osteoclasts (bone dissolving cells) 3,9
- Small amount of connective tissue fibers
- The endosteum cells and fibers form a type of connective tissue called loose connective tissue 15.
- Blood vessels. Endosteum gets blood via perforating arteries that enter the bone through nutrient foramens 11,16.
- Autonomic nerve fibers (which regulate the tone of blood vessels) 12
- References: 1,3,9
Picture 2. Endosteum structure
(free image use)
Difference Between Endosteum and Periosteum
|Location||Medullary canal, spongy bone, Volkmann’s and Haversian canals of all bones||Outer bone surfaces, except articular surfaces; not in sesamoid bones (patella)|
|Structure||A single cellular layer, loose connective tissue||Two layers: fibrous and cellular layer (cambium), dense irregular connective tissue|
|Thickness||~10 micrometers (0.01 mm) 13||0.1-0-5 mm|
|Function||Bone growth, remodeling, repair||Bone growth, remodeling, repair, bone sensitivity, nourishment|
Examples of Endosteum Disorders
- Endosteal sclerosis in sclerosing osteomyelitis 7.
- PubMed (Bone lining and hematopoiesis)
- Medscape (Description of bone healing)
- Inkling.com (Structure of bones)
- Virginia.edu (Bone formation)
- Wiley.com (Bone remodelling in human ribs)
- PubMed (Endosteal cells in human iliac bone)
- Oxfordjournals.org (Sclerosing osteomyelitis)
- Augustatech.edu (Bones and bone tissue)
- Montgomerycollege.edu (Osseous tissue and skeletal structure)
- PubMed Central (Aneurysmal bone cyst in patella)
- Asnjournals.org (Normal bone anatomy and physiology)
- Springer.com (Physiology of bone formation and remodeling)
- Nuclear Medicine Radiation Dosimetry: Advanced Theoretical Principles, y. 2010, p.512 (Endosteum thickness)
- General Principles of Orthopedics and Trauma, y. 2013, p.5 (Stages of fracture healing)
- Etsu.edu (Skeletal system)
- Orthobullets.com (Bone circulation)