What is the Difference Between Compact and Trabecular Bone

The main difference between compact and trabecular bone is that compact bone is a tough and heavy bone made up of compactly packed osteons whereas trabecular bone is a soft and light bone made up of loosely packed trabeculae. Furthermore, compact bones make up the shaft of long bones while trabecular bones make up the ends of long bones. 

Compact and trabecular bone are the two types of bone tissues that make up the structural bones. Compact bone is also known as the cortical bone while the trabecular bone is also known as the cancellous or spongy bone. 

Key Areas Covered 

1. What is Compact Bone
     – Definition, Structure, Function
2. What is Trabecular Bone
     – Definition, Structure, Function
3. What are the Similarities Between Compact and Trabecular Bone
     – Outline of Common Features
4. What is the Difference Between Compact and Trabecular Bone
     – Comparison of Key Differences

Key Terms 

Compact Bone, Osteoblasts, Osteon, Trabeculae, Trabecular Bone

What is Compact Bone 

A compact bone is a type of cortical bone tissue that makes up the hard-outer shell of a bone. Therefore, this type of bone is less porous and strong. Especially, it forms the shaft of the long bones. It contains a marrow cavity which consists of yellow bone marrow, storing fat. Other than providing the structural support and sites for the attachment of muscles, compact bones serve as stores of minerals, aiding mineral homeostasis.

Figure 1: Compact Bone Structure

Furthermore, osteons are the functional units of a compact bone. They surround a tiny, central canal known as Haversian canal. Also,  osteogenic cells are responsible for secreting bone matrix as a ring known as lamella. Here, the bone matrix is made up of hydroxyapatite rich in calcium and phosphorus. Additionally, osteocytes in adult bones occur in cavities known as lacunae. However, canaliculi are the tiny canals that provide nutrients and oxygen to osteocytes. The canaliculi connected to lacunae are responsible for the intercellular communication of osteocytes, forming concentric layers of lamellae around the central canal.  

What is Trabecular Bone 

Trabecular bone is a type of bone tissue which makes up the inner cavity of the bone. It is more porous and lighter than compact bone. Also, the long bones contain trabecular bone in their enlarged ends. In addition, trabecular bone is the major components of the ribs as well as the shoulder blades and flat bones of the skull. Most short flat bones of the skeleton are also composed of trabecular bones. 

Figure 2: Trabecular Bone Structure

Moreover, the main functional unit of a trabecular bone is the trabecula. Trabeculae form a structural framework filled with red bone marrow, which undergoes hematopoiesis. Therefore, trabecular bones have high metabolic activity. Furthermore, osteoblasts align along the trabeculae and are responsible for converting trabecular bone to compact bone by the deposition of bone matrix around trabeculae.  

Similarities Between Compact and Trabecular Bone 

• Compact and trabecular bone are the two types of bone tissue found in the body of animals. 
• Their main function is to make up the skeletal system, which provides the shape and support to the animal. 
• Also, they provide sites for the attachment of muscles. 
• Furthermore, both types of tissue contain osteoblasts and osteoclasts that are responsible for creating bones.  
• They contain osteoids, the collections of collagen and other proteins. 
• Additionally, they contain inorganic mineral salts within the matrix. 
• Besides, both contain nerves, blood vessels, and bone marrow. 
• Moreover, they contain cartilage and membranes including endosteum and periosteum. 

Difference Between Compact and Trabecular Bone 

Definition 

Compact bone refers to the denser material used to create much of the hard structure of the skeleton while trabecular bone refers to a very porous type of bone, which is highly vascularized. Thus, this is the main difference between compact and trabecular bone.

Other Names 

Compact bone is also known as the cortical bone while the trabecular bone is also known as spongy bone or cancellous bone.  

Location 

Compact bone makes up the outer covering of bone while the trabecular bone makes up the inner cavity of a bone. Thus, this is an important difference between compact and trabecular bone.

Occurrence 

Moreover, while compact bone forms the major parts of long bones such as arms and legs,  trabecular bone forms the major parts of short bones such as wrists and ankles. 

In Long Bones  

In addition, compact bones make up the shaft of long bones while trabecular bones make up the ends of long bones. 

The shape of the Bone 

The shape of the bone is also a difference between compact and trabecular bone. Compact bone is cylindrical while trabecular bone is cuboidal.  

Functional Unit 

Furthermore, the functional unit of a compact bone is an osteon while the functional unit of a spongy bone is a trabecula. 

Spaces between Lamellae 

Compact bone does not have spaces between lamellae while trabecular bone has spaces between lamellae.  

Marrow Cavity 

Another difference between compact and trabecular bone is that the former has a marrow cavity while the latter does not have a marrow cavity. 

Bone Marrow 

Whereas compact bone contains yellow bone marrow, trabecular bone contains red bone marrow. 

Amount of Calcium 

Compact Bone contains a high amount of calcium while trabecular bone contains a very low amount of calcium. 

Contribution to the Weight of the Skeleton 

Besides, compact bones take 80% of the weight of the skeleton while trabecular bones take 20% of the weight of the skeleton. 

Porosity 

 One other difference between compact and trabecular bone is that compact bone is less porous while the trabecular bone is more porous. 

Strength 

A compact bone can withstand the weight of up to 5000 pounds while a trabecular bone cannot withstand high weights.  

Function 

The functional difference between compact and trabecular bone is that the former is responsible for providing structural support to the body while the latter acts as a buffer for compact bones. 

Conclusion 

Compact bone is a hard, less porous bone tissue, which makes up the outer layer of bones. The functional unit of a compact bone is the osteon. Moreover, it forms the shaft of the long bones. Additionally, yellow bone marrow occurs inside long bones. On the other hand, trabecular bone is soft and porous bone tissue, which makes up the inner cavity of the bones. The functional unit of a trabecular bone is the trabeculae. It forms the ends of the long bones. Inside the trabecular bone, red bone marrow occurs. Therefore, the main difference between compact and trabecular bone is the structure and function. 

References:

1. Newman, Tim. “Bones: Types, Structure, and Function.” Medical News Today, MediLexicon International, 11 Jan. 2018, Available Here.

Image Courtesy:

1. “605 Compact Bone” By OpenStax Anatomy and Physiology – (CC BY 4.0) via Commons Wikimedia
2. “606 Spongy Bone” By OpenStax College – Anatomy & Physiology, Connexions Web site. Jun 19, 2013. (CC BY 3.0) via Commons Wikimedia