Last Updated on January 30, 2025
Cortical bone and cancellous bone are two types of osseous tissues of the human skeleton which differ in their structure and distribution. The difference in their structures and distribution is designed to carry different functions.
Bone Composition
The bone consists mainly of
- collagen fibers
- inorganic bone mineral
- water
About 70 percent of bone mass is formed by minerals. 10-20% is water.
Calcium and phosphorus are major bone minerals and form crystals in form of hydroxyapatite [Ca10(PO4)6(OH)2].
Depending on the way these elements are arranged, the bone can be cortical or cancellous. The cancellous bone is also called trabecular due to the arrangement of bone-forming structures in trabeculae.
At the microscopic level, the structural arrangement of a cortical bone is different than cancellous. Compact bone consists of closely packed osteons or Haversian systems. The osteon consists of a central canal called the osteogenic (Haversian) canal, which is surrounded by concentric rings (lamellae) of the matrix.
Microscopically, cancellous bone consists of plates (trabeculae) and bars of bone adjacent to small, irregular cavities that contain red bone marrow.
The amount and proportion of trabecular and cortical bone at a given skeletal site affect bone strength independently.
What is Cortical Bone
A typical example of cortical bone is a long bone like the tibia or femur. A cortical bone is a hollow cylindrical bone where the hollow cavity is medulla and the covering layer of bone is called the cortex.
Cortical bone is also called compact or lamellar bone. It provides strength to all the long bones of the body, for example, the femur.
Cortical bone contributes about 80% of the weight of a human skeleton. It is much denser than cancellous bone, harder, stronger, and stiffer.
Compact bone consists of closely packed osteons or Haversian systems. The osteon consists of a central canal called the osteogenic (Haversian) canal, which is surrounded by concentric rings (lamellae) of the matrix.
Between the rings of the matrix, the bone cells or osteocytes are present in the spaces called lacunae. Small channels called canaliculi radiate from the lacunae to the osteonic or Haversian canal to provide passageways through the hard matrix.
These Haversian systems are packed tightly together to form what appears to be a solid mass. The osteonic canals contain blood vessels that are parallel to the long axis of the bone. These blood vessels interconnect with vessels on the surface of the bone. via perforating vessels.
[Read more on Anatomy and Physiology of bone]
Image Credit: Public domain image, from Wikipedia
Cortical bone is arranged to facilitate the following functions
- To support the whole body weight
- Protect organs
- Provide levers for movement
- Store and release calcium.
Cancellous Bone or Spongy Bone
Cancellous bone is also called trabecular bone or spongy bone.
Compared to compact bone, which is the other type of osseous tissue, it has a higher surface area but is less dense, softer, weaker, and less stiff.
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It typically occurs at the ends of long bones, proximal to joints, and within the interior of vertebrae. For example, the distal end radius, proximal humerus, or proximal femur, all are examples of cancellous bone.
Microscopically, cancellous bone consists of plates (trabeculae) and bars of bone adjacent to small, irregular cavities that contain red bone marrow.
The canaliculi connect to the adjacent cavities, instead of a central Haversian canal, to receive their blood supply.
The trabeculae may appear to be arranged haphazardly, but they are organized to provide maximum strength similar to braces that are used to support a building.
The trabeculae of spongy bone follow the lines of stress and can realign if the direction of stress changes.
Cancellous bone has a greater surface area and is ideal for metabolic activity e.g. exchange of calcium ions.
In osteoporosis, cancellous bone is more severely affected than cortical bone.
Cancellous bone is highly vascular and frequently contains red bone marrow where hematopoiesis, the production of blood cells, occurs. Bone marrow also acts as a source of stem cells.
All the procedures for the study of bone marrow are done in spongy bone.
Both cortical and cancellous bones together form the skeleton and serve their respective functions.
References
- Morgan EF, Unnikrisnan GU, Hussein AI. Bone Mechanical Properties in Healthy and Diseased States. Annu Rev Biomed Eng. 2018 Jun 4;20:119-143. doi: 10.1146/annurev-bioeng-062117-121139.
