Topics

Topic

design image
Flexor tendon synovial sheath

The flexor tendon synovial sheath is a double-layered tubular synovial envelope surrounding the flexor digitorum profundus (FDP) and flexor digitorum superficialis (FDS) tendons as they pass through the fibro-osseous tunnel of each finger.

It provides lubrication, protection, and smooth gliding for tendons during flexion and extension, allowing high-precision digital movement with minimal friction. Each sheath forms part of the fibro-osseous digital canal, which includes the annular and cruciform pulleys that maintain tendon alignment against the phalanx.

The synovial sheath also houses the mesotendon, supplying vascular branches to the tendons. Because of its closed compartmental structure, it is clinically important in tenosynovitis, infection spread, trigger finger, and post-traumatic adhesions.

MRI Appearance

T1-weighted images

  • Synovial sheath: Thin low-signal (dark) lining around tendon

  • Tendons: Low-signal linear structures surrounded by sheath

  • Fatty tissue around sheath: Bright

  • Fluid inside sheath (if present physiologically): Usually minimal, low-to-intermediate signal

T2-weighted images

  • Synovial sheath: Thin low-signal wall

  • Tendons: Low-signal

  • Normal synovial fluid: Bright

  • Pulleys: Very low-signal curvilinear bands

  • Excellent contrast between tendons, sheath, and phalanges

STIR

  • Synovial sheath: Low-to-intermediate signal

  • Tendons: Dark linear bands

  • Fat signal suppressed

  • Normal fluid: Bright

  • Sheath margins sharply visible against suppressed surroundings

MRI image

Flexor tendon synovial sheath hand MRI axial image-img-00000-00000