Tendons – Structure, Function and Conditions

What Are Tendons?

Tendons (Latin: Tendo, plural: Tendines) are cord-like or strap-like structures made of dense fibrous connective tissue. They connect skeletal muscles to bones and transmit the force generated by the muscle to the skeleton, making purposeful body movement possible. Without tendons, muscles would be unable to produce directed movement.

Structure and Composition

Tendons are composed primarily of collagen fibers – mainly collagen type I – arranged in parallel bundles. This structure gives tendons exceptionally high tensile strength while remaining relatively inelastic. Key structural components include:

• Collagen fibrils: The smallest building units, grouped into larger fiber bundles.
• Tenocytes: Specialized fibroblast cells that produce and maintain the collagen matrix.
• Endotenon: Fine connective tissue surrounding individual fiber bundles, containing blood vessels and nerves.
• Epitenon: The outer connective tissue sheath that encloses the entire tendon.
• Tendon sheath (Vagina tendinis): In certain locations (e.g., hands and feet), a synovial sheath surrounds the tendon, reducing friction and improving gliding ability.

Function

The primary function of tendons is to transmit muscle contraction forces to the bone, enabling joint movement. They also serve several other important roles:

• Force transmission: Relaying muscular force to bone for controlled movement.
• Energy storage: Elastic tendons such as the Achilles tendon can temporarily store kinetic energy and release it (spring-like effect).
• Joint stabilization: Tendons contribute to passive stabilization of joints.
• Proprioception: Tendons contain mechanoreceptors (Golgi tendon organs) that relay information about muscle tension and body position to the brain.

Major Tendons in the Human Body

The human body contains numerous tendons. Among the most well-known and clinically relevant are:

• Achilles tendon (Tendo calcaneus): The strongest and thickest tendon in the body; connects the calf muscles to the heel bone.
• Patellar tendon (Ligamentum patellae): Connects the kneecap to the tibia and is essential for knee extension.
• Rotator cuff: A group of four tendons surrounding the shoulder joint, providing stability and mobility.
• Biceps tendon: Connects the biceps muscle to the shoulder joint and the forearm bone.
• Finger flexor and extensor tendons: Enable fine motor control of the hand.

Common Tendon Conditions

Tendinitis (Tendon Inflammation)

Tendinitis is an inflammation of the tendon, often caused by overuse, improper loading, or injury. Typical symptoms include pain, swelling, and restricted mobility in the affected area.

Tendinopathy

Tendinopathy refers to degenerative changes in the tendon structure without classic signs of inflammation. It is common in athletes and older individuals and presents as chronic pain and reduced load-bearing capacity.

Tendon Rupture

A tendon rupture involves a partial or complete tear of the tendon. This can result from sudden intense stress (e.g., Achilles tendon rupture during sports) or from degenerative pre-existing damage. Typical signs include an audible snap, sudden pain, and loss of function.

Tendovaginitis (Tendon Sheath Inflammation)

Tendovaginitis is an inflammation of the tendon sheath, most commonly affecting the hand and wrist. It is characterized by pain during movement and a creaking or crepitus sensation along the tendon.

Diagnosis of Tendon Problems

Tendon conditions are diagnosed using several methods:

• Clinical examination: Palpation, range-of-motion tests, and specific provocation tests.
• Ultrasound (sonography): Imaging technique for direct visualization of tendon structure, thickening, tears, or inflammation.
• Magnetic resonance imaging (MRI): Detailed cross-sectional imaging for complex or deep tendon changes.
• X-ray: To rule out associated bone injuries or calcifications within the tendon.

Treatment of Tendon Conditions

Treatment depends on the type and severity of the tendon condition:

• Conservative therapy: Rest, ice application, physiotherapy, eccentric strength training, and anti-inflammatory medications (e.g., NSAIDs).
• Shockwave therapy: A non-invasive method to stimulate tendon regeneration in chronic tendinopathies.
• Injection therapies: Corticosteroids for short-term anti-inflammatory effects, or platelet-rich plasma (PRP) to promote healing.
• Surgical treatment: In cases of complete ruptures or treatment-resistant symptoms, surgical repair or reconstruction of the tendon may be required.

Tendon Health and Prevention

Tendons can be strengthened and protected from injury through targeted measures:

• Regular warm-up before physical activity
• Progressive training load without abrupt increases
• Adequate recovery time after intense physical activity
• Eccentric strength training to reinforce tendon structure
• Balanced nutrition with sufficient collagen precursors (vitamin C, amino acids)

References

1. Schiebler, T.H. & Korf, H.W. (2007). Anatomie: Histologie, Entwicklungsgeschichte, makroskopische und mikroskopische Anatomie, Topographie. Steinkopff Verlag.
2. Docking, S.I. & Cook, J. (2019). How do tendons adapt? Going beyond tissue responses to understand positive adaptation and pathology development. Journal of Orthopaedic Research, 37(6), 1205–1215.
3. World Health Organization (WHO). Musculoskeletal conditions. Retrieved from: https://www.who.int/news-room/fact-sheets/detail/musculoskeletal-conditions