The key difference between interstitial and appositional growth is that interstitial growth is the longitudinal growth of bone which increases the length of the bone while appositional growth is the bone growth which increases the diameter of the bone.
Bones can grow. They can increase in length as well as in diameter or thickness. Moreover, they are highly active organs which can repair themselves when injured. Bones are formed from cartilages. We call this process ossification. Soft cartilages gradually turn into hard bones.
CONTENTS
1. Overview and Key Difference
2. What is Interstitial Growth
3. What is Appositional Growth
4. Similarities Between Interstitial and Appositional Growth
5. Side by Side Comparison – Interstitial vs Appositional Growth in Tabular Form
6. Summary
What is Interstitial Growth?
Interstitial growth is a bone growth which results in the lengthening of the bone. This growth occurs within the lacunae. It happens due to the cell division in the proliferative zone and the maturation of cells in the zone of maturation. Cartilage lengthens and is replaced by bone tissue during interstitial growth.
Figure 01: Interstitial Growth
As a result of interstitial growth, long bones continue to lengthen. Interstitial growth happens, and bones continue to grow in length until early adulthood. At the end of adolescence, when chondrocytes stop dividing by mitosis, interstitial growth ceases.
What is Appositional Growth?
Appositional growth is the second type of growth which increases the bone width or diameter. This growth occurs as a result of depositing new bone tissue on the endosteal and periosteal surfaces. Therefore, new layers are formed on the surface of pre-existing bones, increasing the thickness of the bone.
Figure 02: Appositional Growth
Appositional growth can even continue after the cease of interstitial growth. During the appositional growth, both bone formation and reabsorption take place. Osteoclasts resorb old bone while osteoblasts produce new bone tissue. Appositional growth not only increases the diameter of the diaphysis but also increases the diameter of the medullary cavity.
What are the Similarities Between Interstitial and Appositional Growth?
- Interstitial and appositional growth are two types of growth shown by bones.
- Both occur in growing bones.
What is the Difference Between Interstitial and Appositional Growth?
Interstitial growth is the increase in the length of bones by the cartilage lengthening and is replacing by bone tissue while appositional growth is the increase in the diameter of bones by the addition of bony tissue at the surface of the pre-existing bone. So, this is the key difference between interstitial and appositional growth. Interstitial growth allows bones to grow in length, while appositional growth allows bones to grow in diameter. Moreover, interstitial growth occurs within lacunae while appositional growth happens on the surface of pre-existing cartilage.
The following infographic tabulates the differences between interstitial and appositional growth for side by side comparison.
Summary – Interstitial vs Appositional Growth
Interstitial growth and appositional growth are two types of bone growth. Due to interstitial growth, long bones continue to lengthen while due to appositional growth, bones increase in width or diameter. Thus, this is the key difference between interstitial and appositional growth. Moreover, interstitial growth occurs within the lacunae while appositional growth occurs on the surface of pre-existing cartilage. Cartilages lengthen and is replaced by bone tissue during the interstitial growth while new bone tissue deposit on the surface of existing bone during the appositional growth.