Preface

The muscles and skeletal system are vital for performing everyday functions. Tendons are round, oval, or flat tissue extending between muscle and bone. Tendons are differentiated muscles that connect to bones. They provide joint movements resulting from contraction and relaxation of muscles. Tendons are highly resistant to tensile force but have a flexible structure. They also have some extension properties. In this manner, they transmit the tension generated by the muscle to the bones and tendons adapt perfectly to the joint regions and bone circumference. Some tendons contain bony or cartilaginous sesamoid bones. These bones allow the tendons to adapt to the bone surface. The tensile strength of the tendons is similar to the bone, and a 1 cm thick tendon can withstand a load of 600–1000 kg.

The musculoskeletal system can be likened to the columns that carry the body. A weak system will cause you to experience discomfort in different parts of your body after a while. A muscle and skeletal system that is strong enough to perform vital functions is extremely important. Walking, running, performing sports, and even moving comfortably, depends on it. With the increasing importance placed on human health, the average life expectancy has started to increase. Improving the quality of life for this longer lifespan has become very important.

The book contains an introductory chapter, which is followed by an overview of the structure and classification of tendons by Kaya et al., including an explanation of their complex structure. The third chapter is about the imaging of tendons by Torres-Ayala et al., where we learn that magnetic resonance imaging and ultrasound are useful radiological methods that allow adequate evaluation of tendon anatomy and integrity. The fourth chapter is on exercise and a tendon remodeling mechanism by de Cassia Marqueti et al. The fifth chapter describes patellar tendinopathy, which is a source of anterior knee pain, characterized by pain localized to the inferior pole of the patella. The author describes patellar tendinopathy as jumper's knee. The sixth chapter by Burk summarizes a very important, yet mostly underestimated subject: mechanisms of action of multipotent mesenchymal stromal cells in tendon disease. The chapter provides an understanding of successful treatment approaches to fully exploit the regenerative potential of the multipotent mesenchymal stromal cells. The seventh chapter is by Yousef and it introduces the physiology of flexor tendon healing and rationale for treatment protocols. This is an interesting chapter on the management of flexor tendon injuries of the hand by Ahmad et al. We use our hands for carrying out most of our daily activities, but these activities can make our hands vulnerable for trauma. The last chapter is written by Lee et al. and it describes an interesting study performed with the injectable rhBMP-2-containing collagen gel for tendon healing in a rabbit extra-articular bone tunnel model. This book may contain errors despite our obsessive reviews and efforts. But all in all, I think that it provides the reader with interesting up-to-date data while summarizing information about tendons.

I want to thank all the authors of this book for their amazing work and our Author Service Manager Ms Rozmari Marijan, without whom I would not have been able to edit this book.

I hope that this book will be useful for anyone who wants to read about new perspectives on tendons. I also hope that it will inspire researchers working in this field.

> **Dr. Hasan Sözen** University of Ordu, Physical Education and Sport, Ordu, Turkey

> > **1**

**Chapter 1**

*Hasan Sözen*

**1. Introduction**

Introductory Chapter: Tendons

The tendons act as a mechanical bridge. Tendons allowing muscle strength to pass to the bones and joints, it also allows the muscle to contract and target movement. There are different types of tendons that reflect muscle morphology and specific functions. Tendon tissue includes all muscle tissue, not just the terminal or starting area of each muscle. The binding layers (epimysium, perimysium, and endomysium) combine in a single organization to contact one or more fixed bone points. There is a contraction fiber in the same tendon near the muscle. It affects the muscle-tendon, and thus the tendon affects the functional function of the muscle. In the context of manual therapy, rehabilitation or surgery, it is important to consider these close relationships between anatomy and function. Tendon tissue can adapt its cellular structure to pathological or physiological stimuli depending on the systemic hormonal environment and age [1]. The primary function of ligaments and tendons is to move from muscles to tendons or to assist movement to transfer force from the bone involved in the movement to the bone (ligaments). Foot and hand tendons net occur in relation to the ligament between them and this is called super-tendons. The concept of super-tendons has been proposed to explain that

such networks exhibit a more functional range than their members [2].

tendon (small tendons, tendinopathic tendons) [3].

lular matrix proteoglycans (**Figure 2**).

In the organism, ligaments and tendons act as connective tissues that act as force-transmitting structures and provide musculoskeletal movement. Typical features of normal tendon tissue are parallel-aligned tenocytes and collagen I fibers. In addition, the extracellular matrix consists of proteoglycans, elastin, and glycoproteins. There is almost no vein in the tissue and nutrition is provided along with oxygen as well as nutrition at the osteotendinous junctions and vascularized myotendinous. Growth factors are vital for tendon homeostasis, development, and regeneration. The most important of these is growth factor-beta. Structural changes on tendinopathy and aging comprise the degree of vascularization (aging leads to less tendinopathy and more vascularization), extracellular matrix (age-related lower collagen content and tendinopathic collagen disorder), and proteoglycan

Tendons' basic structural properties situations are combined and shown in **Figure 1**. The main differences in morphology and organization of collagen fibers, has in terms of vascularization and cell density and morphology. In addition, extracellular matrix proteins in the normal aging and degenerative change the condition of the tendon and ligament [4]. Aging tendon tissue is different in terms of the tendon cells from healthy tissue morphology and finer turn into tenocytes have larger nuclei in older age. As for the vascularization is reduced and there are fat deposits in the connective tissue. Finally, tendinopathic tendon is more vascularized than normal tendon with irregular collagen fibers and the enriched with extracel-

According to the figure, healthy tendon tissue consists of densely packed collagen fibers in an amorphous ground material containing connective tissue of
