Tendon Structure and Classification

*Murat Kaya, Nazım Karahan and Barış Yılmaz*

### **Abstract**

Tendons play an important role in the movement by transmitting the contraction force produced by the muscles to the bone they hold, and their contribution to stability to the joints is extremely important. Tendons generally have a very complex structure; they are actually heavily composed of connective tissue and have a small number of cells and rich extracellular matrix, similar to other connective tissue structures. The tendons are mainly composed of three parts: the tendon itself, the muscle-tendon junction, and the bone insertion. The simplest classification for the tendons classified according to their shapes, settlements, and anatomical structures is the classification made according to their shapes. 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 intraarticular and extraarticular. According to their anatomy, the tendons can also be classified as sheathed or synovial-coated or unsealed or paratenon-coated. According to their functions, tendons can be classified as energy storage or positional tendons.

**Keywords:** tendon, tendon structure, tendon classification, fascicle, endotenon, epitenon, paratenon, collagen fibrils

### **1. Introduction**

Tendons are dense fibrous tissues that bind the muscles to the bone. They play an important role in the movement by transmitting the contraction force produced by the muscles to the bone they hold. At the same time, their contribution to stability to the joints is extremely important. Although they differ in shape and size depending on the location, the common feature of all is that they can attach to a bone and transmit large loads without deforming them. Although they are structurally sound as they can withstand very high powers due to their function, degeneration and various damages caused by aging can result in loss of muscle strength [1–3].

Although tendons generally have a very complex structure, they are actually heavily composed of connective tissue and have a small number of cells and rich extracellular matrix, similar to other connective tissue structures. In terms of total tissue volume, while the cellular structure constitutes approximately 20% of total tissue volume, the remaining cells form 80% of the extracellular matrix. As a result of these factors, the cellular structure is mainly 60–85% collagen, 0.2% proteoglycans such as inorganic substances, 2% elastin, and 4.5% other proteins, while the matrix is composed of 55–70% water and the rest of the extracellular matrix consists of proteoglycans [4, 5].

**4**

*Tendons*

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2018

Limited; 2010

Elsevier

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