**3. Classification of tendons**

The tendons are mainly composed of three parts: the tendon itself, the muscletendon junction, and the bone insertion. In general, they pass through the joints and adhere to their distal. In this way, they increase the effectiveness of the muscles on the joints. At the same time, similar to bones, mechanical properties vary depending on the load carrying place. For this reason, knowing where they are helps us understand the structure. In fact, not every muscle has a tendon. While some tendons are involved in some muscles that play an active role in joint movements, the presence of some tendons is to increase muscle movement distances rather than the movement of the joint. For example, Achilles tendon is a very special tendon for the body carrying the loads by centralizing the strength of a few muscles. In contrast, some tendons, such as the posterior tibial tendon, act by distributing the load to several bones. Although it is known that most tendons originate from the muscle and adhere to the bone, some tendons may be the starting point for muscles, or two muscles are connected to each other through a tendon [22, 23].

The simplest classification for the tendons classified according to their shapes, settlements, and anatomical structures is the classification made according to their shapes. They can be very small and very long, and they can be very large and very short. Tendons are very variable according to their shape, long, round, ropeshaped (such as Achilles tendon), or short; flat tissue adhesion (such as bicipital aponeurosis) can be seen. In other words, tendons may change from flat to cylinder, from fan shape to ribbon shape. However, round tendons (such as flexor digitorum profundus) or flat tendons (such as rotator cuff, bicipital aponeurosis) are more involved in the body. In this simple classification, tendons are divided into round and flat and are very different from each other as structural and functional. For example, while round tendons respond equally to tensile loads with parallel collagen patterns, flat tendons such as rotator cuffs can respond microanatomically in the form of compression and shear forces due to longitudinal, oblique, and transverse collagen sequences. However, in round tendons, the section area is proportional to the maximum isometric strength of the muscle. In other words, due to parallel collagen sequences, flat tendons are resistant to compression and shear forces due to flat, longitudinal, and oblique collagen sequences in comparison to round tendons that respond equally to the tensils [3, 24].

Tendons can be classified in many ways according to their location, but the most logical one is the tendon classification in relation to the functions they see as the intraarticular (biceps long head and popliteus tendon) and the extraarticular (Achilles tendon). Most tendons are non-articular, but the intra-articular ones lack the ability to repair after injury as in the same intra-articular ligaments (an example of anterior cruciate ligament tear). At the same time, although most tendons adhere to the bone, some tendons form the origo point for the muscles (lumbrical muscles originate from the flexor digitorum profundus) or connect two muscles (such as


### **Table 1.**

*Classification and properties of tendons according to their functions.*

omohyoid and digastric muscle). In addition, the large part of the tendon may originate from the muscle itself (gastrocnemius and soleus). For example, in some muscles tendons move into the muscle joint and tendon sticks at an angle. This allows a high proportion of muscle fibers to adhere to the tendon, thereby increasing the strength of the muscle-tendon unit but reducing the range of motion.

According to their anatomy, the tendons can also be classified as sheathed or synovial-coated (such as the long flexor of the fingers) or unsealed or paratenoncoated (such as Achilles tendon). In other words, these tendons, which are separated by intrasynovial and extrasynovial, have a higher slippage resistance compared to the intrasynovial tendon structure, when examined more closely. At the same time, the soft tissue protection and vascularity of these two tendons are different [20].

According to its functions, tendons can be classified as energy storage or positional tendons (**Table 1**). In general, the muscles tend to tendon to shorten the stress load; the affected tendon is stretched and the muscle can relax again when relaxed. This makes the tendon a structure that stores elastic voltage energy. The best example of energy storage tendons is Achilles tendon. Tibialis anterior tendons in human are examples of positional tendons, and they can never extend relatively. Positional tendons are rarely injured because they extend less [25–27].

### **4. Conclusion**

In conclusion, tendons are composed of multiple bundles, fibroblast, and dense linear collagen fibrils, which form the macroscopic structure of tendons and give the fibrous appearance. The cell and matrix compositions of tendons are similar to ligaments and capsules and contain only small differences. In fact, they all have the same cell type and similar vascular and innervation sources. The extracellular matrix of tendons is largely composed of collagen fiber network and less proteoglycans, elastin, and other proteins. The main task of these components is to maintain the structure of the tendon and facilitate the biomechanical reaction of the tissue against mechanical loads.

Knowing where tendons are helps us understand the structure. While some tendons are involved in some muscles that play an active role in joint movements, the presence of some tendons is to increase muscle movement distances rather than the movement of the joint.

**11**

**Author details**

Hospital, Diyarbakır, Turkey

Murat Kaya1

provided the original work is properly cited.

\*, Nazım Karahan<sup>2</sup>

Education and Research Hospital, Istanbul, Turkey

\*Address all correspondence to: kayamuratdr@gmail.com

*Tendon Structure and Classification*

*DOI: http://dx.doi.org/10.5772/intechopen.84622*

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

and Barış Yılmaz1

1 Department of Orthopedic Surgery and Traumatology, Fatih Sultan Mehmet

2 Department of Orthopedic Surgery and Traumatology, Selahaddin Eyyubi State

*Tendon Structure and Classification DOI: http://dx.doi.org/10.5772/intechopen.84622*

*Tendons*

Material specifications

Biomechanical features

**Table 1.**

omohyoid and digastric muscle). In addition, the large part of the tendon may originate from the muscle itself (gastrocnemius and soleus). For example, in some muscles tendons move into the muscle joint and tendon sticks at an angle. This allows a high proportion of muscle fibers to adhere to the tendon, thereby increasing the strength of the muscle-tendon unit but reducing the range of motion. According to their anatomy, the tendons can also be classified as sheathed or synovial-coated (such as the long flexor of the fingers) or unsealed or paratenoncoated (such as Achilles tendon). In other words, these tendons, which are separated by intrasynovial and extrasynovial, have a higher slippage resistance compared to the intrasynovial tendon structure, when examined more closely. At the same time, the soft tissue protection and vascularity of these two tendons are

**Energy storage tendons Positional tendons**




content, the harder matrix -Tightly packed fascicles with less interfascicular slip at low loads


the bones

Function -Storage and release of elastic stress energy

content, softer matrix


*Classification and properties of tendons according to their functions.*

Injury -More -Less




Example -Achilles tendon -Anterior tibial tendon

According to its functions, tendons can be classified as energy storage or positional tendons (**Table 1**). In general, the muscles tend to tendon to shorten the stress load; the affected tendon is stretched and the muscle can relax again when relaxed. This makes the tendon a structure that stores elastic voltage energy. The best example of energy storage tendons is Achilles tendon. Tibialis anterior tendons in human are examples of positional tendons, and they can never extend relatively.

In conclusion, tendons are composed of multiple bundles, fibroblast, and dense linear collagen fibrils, which form the macroscopic structure of tendons and give the fibrous appearance. The cell and matrix compositions of tendons are similar to ligaments and capsules and contain only small differences. In fact, they all have the same cell type and similar vascular and innervation sources. The extracellular matrix of tendons is largely composed of collagen fiber network and less proteoglycans, elastin, and other proteins. The main task of these components is to maintain the structure of the tendon and facilitate the biomechanical reaction of the tissue

Knowing where tendons are helps us understand the structure. While some tendons are involved in some muscles that play an active role in joint movements, the presence of some tendons is to increase muscle movement distances rather than

Positional tendons are rarely injured because they extend less [25–27].

**10**

different [20].

**4. Conclusion**

against mechanical loads.

the movement of the joint.
