Tendon

A tendon is a fibrous connective tissue that attaches a muscle to a bone, enabling the transfer of muscular force to produce movement. Tendons are mainly composed of dense regular connective tissue rich in type I collagen fibers aligned in parallel to withstand uniaxial tension. They store and dissipate elastic energy during locomotion, contributing to mechanical efficiency and joint stability.

Anatomically, tendons consist of collagen fibrils organized into fascicles, surrounded by the epitenon, and, in some cases, a synovial sheath (the tenosynovium) or a surrounding loose tissue layer called the paratenon. Blood supply is relatively limited, with vessels entering from the surrounding connective tissue and the bone-tendon junction. Innervation includes sensory nerves that convey pain and proprioceptive information. The tendon inserts into bone at the enthesis, a site capable of adapting to mechanical load, and some tendons develop specialized structures to handle shear or sliding within a sheath.

Clinically, tendons are prone to overuse injuries and degeneration. Tendinopathy encompasses inflammatory and non-inflammatory conditions such as tendinitis and tendinosis, presenting with localized pain, tenderness, and sometimes swelling. Tenosynovitis refers to inflammation of the tendon’s synovial sheath. Acute rupture can occur with sudden overload or age-related degeneration. Diagnosis typically relies on clinical examination supplemented by imaging such as ultrasound or MRI. Management emphasizes gradual loading and rehabilitation, often with eccentric exercises, activity modification, and analgesia as appropriate; surgical repair may be required for rupture or refractory cases. Healing is slow due to limited vascularity and may result in altered tendon properties and scar tissue.