Human skeleton is made of two types of osseous tissues which differ in their structure and distribution. The difference in their structures and distribution is designed to carry different functions.
What is Cortical Bone
Cortical bone refers to the thick outer surface of typically a long bone that ensheathes the cacity of the bone called medulla. The sheath or outer shell formed by the cortical bone is called cortex. Cortical bone is also called compact or lamellar bone and provides strength to all the long bones of the body, for example, femur.
Cortical bone contributes about 80% of the weight of a human skeleton. bones. It is much denser than cancellous bone, harder, stronger and stiffer.
At 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 matrix.[See diagram below]
Between the rings of matrix, the bone cells (osteocytes) are located in spaces called lacunae. Small channels (canaliculi) radiate from the lacunae to the osteonic (haversian) canal to provide passageways through the hard matrix.
The 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, by way of perforating canals, with vessels on the surface of the bone.
[Read more on Anatomy and Physiology of bone]
Image Credit: Public domain image, from Wikipedia
Cortical bone is arranged for facilitating the following functions
- To support the whole body weight
- Protect organs
- Provide levers for movement
- Store and release calcium.
Cancellous 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.
Image Credit:OERPUB
It typically occurs at the ends of long bones, proximal to joints and within the interior of vertebrae.
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. It may appear that the trabeculae are arranged in a haphazard manner, 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.
Both cortical and cancellous bones together form the skeleton and serve their respective functions.
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Bone is a important thing on our body parts as I think That is why we need know about bone as well. In this post you’ve shared some important info about the Types of Bone – Cortical and Cancellous as well. This is really effective to all. Thanks!!!
Thanks a lot. Helped me so much to understand the difference between the two. 🙂
Great job summarizing and comparing the two types of bone tissue. I’m just unsure about the last paragraph which states that cancellous bone is highly vascularized, as spongy bone does not contain blood vessels.
I am glad Bhagyashree it helped you.
Thanks for the appreciation. Cancellous bone is very vascular. It has to be because it is the place where blood cells are formed by marrow.
any one help me my mother left leg is bone cortices are intact
Would cortical and cancellous bone explain color variation on an MRI? Black vs very light gray? Or would light gray almost white coloring be of concern on an MRI?
The cortices are blacker, medulla almost looks similar. The concern should arise if the difference is focal rather than widespread. If you are able to put across your specific concern, I would be in better position to reply.
My 10 year old daughter broke her tarsal bone in her foot. It got hit with a bowling ball ( significant force). This is her 3rd broken bone. X Ray was questionable so they ordered an MRI. It showed the break in much better detail. The doctor was concerned about the color contrast from the bottom of the tibia (dark) to the tarsal (white or light grey). From my best recollection……
I wish I had a second look at the MRI because then I would have measured certainty of what I’m relating to you. But for discussion sake, let’s pretend that’s the exact concern of the bones mentioned. I do recall him saying possibly osteomalasia? He ordered blood work as precaution, vitamin D and calcium, all minerals were nominal. So what could be left or overlooked? I’ll get better information if necessary. Thanks so much for your input!
Lars Edwards,
I understand that you are concerned about something doctor said but there are too many ifs and buts to answer it in proper way. But I do understand that sometimes incidental findings could also be significant.
I think the best way is to discuss it with the treating doctor, understand the concerns raised and their implications. If there is an MRI finding that bothers, review of the image from radiologist can be asked.
Osteomalacia as term is used in adults. In children, the similar condition is called rickets[some authors do call it pediatric osteomalacia]. In rickets, the bone keeps growing at the end but the calcification is delayed. But I doubt that could cause of darker bone. [Its further confusing that MRI has two kinds of images T1 and T2 weighted and I do not even know what you may be referring to]
Please talk to your doctor and ask it is wiser to investigate further or okay to wait and watch.
Take care.