Tendons

Tendons are fibrous connective tissues that connect muscle to bone, transmitting the force of muscle contraction to generate movement. They are composed mainly of type I collagen, arranged in parallel fibers that form fascicles, and contain tenocytes in an extracellular matrix rich in proteoglycans and other matrix proteins. The tissue has a hierarchical organization from collagen molecules to fibrils, fibers, and the whole tendon, which supports its tensile strength.

Tendons are viscoelastic structures that can store elastic energy during loading and release it during propulsion. Their fibers are aligned with the direction of force, maximizing resistance to tension. The mid-substance tends to have comparatively poorer blood supply, while vascularization comes from the muscle-tendon junction and the bone-tendon insertion, often with a surrounding synovial sheath in certain tendons. Innervation provides sensory feedback and proprioception, contributing to motor control and joint stability.

Functionally, tendons transfer force from muscle to bone to produce movement, contribute to joint stability, and act as energy stores that improve locomotion efficiency. They also play a role in proprioceptive sensing, helping regulate muscle activity.

Common clinical issues involve tendinopathies and ruptures. Tendinopathies encompass inflammatory tendinitis and degenerative tendinosis, with frequent involvement of the Achilles, rotator cuff, patellar, and lateral elbow tendons. Healing is slow due to limited blood flow, and management emphasizes graded loading, often with eccentric exercises, along with rest and rehabilitation. Surgery may be required for complete ruptures or severe degenerative tears. Diagnosis relies on history, examination, and imaging such as ultrasound or magnetic resonance imaging to assess structure and integrity.