Surface Markings of Synovial Sheaths of the Flexor Tendons

Topic Overview

Common Flexor Synovial Sheath (Ulnar Bursa)

• Extends above the flexor retinaculum (lower transverse crease of wrist) for about 2.5 cm into the forearm.

• Medial border: Lateral edge of the tendon of flexor carpi ulnaris.

• Lateral border: Roughly along the tendon of palmaris longus.

• Becomes narrower behind the flexor retinaculum and broadens below it in the palm.

• Most of the sheath terminates at the upper transverse crease of the palm, but the medial portion continues to the distal transverse crease of the little finger (hence, continuous with the little finger synovial sheath).

• Clinical note: infection in the ulnar bursa may spread to the forearm or along the little finger (“horseshoe abscess”).

Synovial Sheath of Flexor Pollicis Longus (Radial Bursa)

• Lies deep to the flexor retinaculum along the tendon of flexor pollicis longus.

• Extends from about 2.5 cm above the flexor retinaculum to the distal phalanx of the thumb.

• This sheath is independent of the ulnar bursa.

• Clinical importance: may communicate with the ulnar bursa in some cases—spread of infection between thumb and little finger can occur through this connection.