Tenosynovitis is a broad term describing the inflammation of the fluid-filled synovium within the tendon sheath. It commonly manifests as pain, swelling, and contractures, depending on the etiology. The condition can affect any tendon in the body surrounded by a sheath but has a predilection for the hand, wrist, and foot. A basic understanding of the tendon anatomy allows the clinician to appreciate the pathophysiology, treatment, and complications. The tendon anatomy and relationship to the tendon sheath are well illustrated in the hand.
The tendons' intricate arrangement in the hand permits the gripping, grasping, and precise motor function of the hand. Shortly after exiting the carpal tunnel at the wrist, the tendons of flexor digitorium superficialis and profundus muscles cross the palm and enter tunnels formed by the fibrous sheaths on the palmar aspect of each digit. Within each tunnel, the tendons are surrounded by a synovial sheath or bursa. Together, the fibrous tunnel and synovial covering form the tendon sheath.
The tendon sheath has the following functions:
The synovial fluid nourishes the tendon and provides a low-friction environment, allowing the smooth gliding of the tendon and reducing wear and tear of the tendons from excessive friction.
The fibrous sheath provides anchor points for the tendon to prevent 'bowstringing.' For example, in the hand, they help anchor the tendons to the bony plane of the phalanges and interphalangeal joints to prevent the tendons from bowing when the digits are flexed.
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