What are synovial sheaths and what is their function?

Synovial sheaths are double-layered tubular sacs that surround long flexor tendons, containing synovial fluid to provide a frictionless surface for tendon movement within osseofibrous tunnels. They facilitate smooth gliding of tendons, reducing wear and tear.

What is the ulnar bursa and which tendons does it enclose?

The ulnar bursa is a synovial sheath that encloses eight tendons: the flexor digitorum superficialis (FDS) and flexor digitorum profundus (FDP) as they pass through the carpal tunnel. It extends proximally and distally from the flexor retinaculum and is continuous with the digital sheath of the little finger.

What is the radial bursa and how does it relate to the thumb?

The radial bursa is a synovial sheath that surrounds the tendon of the flexor pollicis longus (FPL). It extends proximally above the flexor retinaculum and is continuous distally with the digital synovial sheath of the thumb, facilitating its movement.

How do digital synovial sheaths differ between fingers?

Digital synovial sheaths surround flexor tendons in each digit, extending from the metacarpal head to the distal phalanx base. The thumb is continuous with the radial bursa, the little finger with the ulnar bursa, and the index, middle, and ring fingers have a gap between the ulnar bursa and their digital sheaths.

What are vincula and what is their role?

Vincula are connective tissue bands (vincula longa and vincula brevia) that connect flexor tendons to phalanges. They transmit blood vessels to the tendons, with each sheath typically having five vincula (two brevia and three longa) to support vascular supply.

What is tenosynovitis and how can it spread in the hand?

Tenosynovitis is an infection or inflammation of the synovial sheath, often from injuries like pin pricks, causing painful swelling from pus accumulation. It can spread from digital sheaths to the ulnar or radial bursae, especially from the thumb or little finger, and potentially extend to the space of Parona in the forearm.

Flexor Tendon Synovial Sheaths – Ulnar & Radial Bursae