tenosynovium

Tenosynovium refers to the synovial membrane that lines a tendon sheath and produces lubricating fluid to reduce friction as a tendon moves within its sheath. It constitutes the visceral, inner layer of the sheath and is part of the joint’s broader synovial system; where a true sheath surrounds a tendon, the tenosynovium forms the lubricated interior surface, while an outer parietal layer forms the surrounding sleeve.

Anatomy and distribution: Tendon sheaths surround many long tendons where gliding motions occur, most notably in the hand (digital flexors and extensors), as well as in the wrist and ankle. In some anatomical regions, tendons are enclosed by a paratenon rather than a complete synovial sheath. When a true tendon sheath is present, the inner surface is the tenosynovium, with a potential space between the layers that contains synovial fluid.

Function: The tenosynovium secretes synovial fluid that lubricates the tendon within its sheath, reducing friction and wear. This lubrication also helps nourish the avascular tendon tissue through diffusion.

Clinical significance: Inflammation of the tenosynovium, or tenosynovitis, is the most common disorder of the tendon sheath. It can be infectious or non-infectious and is associated with pain, swelling, warmth, and decreased range of motion. Common examples include de Quervain’s tenosynovitis of the wrist and stenosing tenosynovitis (trigger finger). Repetitive motion, inflammatory diseases, infection, or trauma are contributing factors.

Diagnosis and treatment: Evaluation relies on clinical examination and, when needed, imaging such as ultrasound or MRI to assess sheath thickening or fluid. Treatments include rest, nonsteroidal anti-inflammatory drugs, splinting, corticosteroid injections into the sheath, and antibiotics if infection is suspected. Refractory cases may require surgical intervention.