Synovial sheath

The synovial sheath is the inner layer of a tendon sheath, composed of a thin synovial membrane that surrounds the tendon and secretes synovial fluid. This fluid lubricates the tendon surface, allowing smooth, friction-free movement as the tendon glides within its fibrous sheath.

The synovial sheath consists of two continuous layers:

• Visceral layer – closely adheres to the tendon surface.

• Parietal layer – lines the inner surface of the fibrous sheath. A narrow synovial cavity between these layers contains synovial fluid.

Function

• Reduces friction between the tendon and fibrous sheath.

• Provides nourishment to the avascular tendon surface.

Example

The synovial sheaths of the flexor tendons in the fingers and extensor tendons on the dorsum of the wrist facilitate efficient, low-friction tendon movement during hand and finger motion.