Thumb Flexor Sheath Exam

  • The thumb has two annular pulleys and a thinner oblique pulley.
  • These pulleys provide the fibrous component of the flexor tendon’s fibro-osseous tunnel.
  • Constricts of the flexor sheath at the A-1 level can cause trigger thumb problems.
  • When a trigger thumb is present there is tenderness at the A-1area and catching and locking of the thumb during active motion.
Diagrams & Photos
  • Locked trigger thumb due to constricted FPL at the A-1 pulley.
    Locked trigger thumb due to constricted FPL at the A-1 pulley.
  • Trigger finger release. Note digital nerves, FPL, and fascia of A-1 pulley (yellow ellipse) cut and flapped ulnarly.
    Trigger finger release. Note digital nerves, FPL, and fascia of A-1 pulley (yellow ellipse) cut and flapped ulnarly. There is visible narrowing of the FPL under the A-1 pulley.
  • Infected swollen thumb flexor tendon sheath (arrow).
    Infected swollen thumb flexor tendon sheath (arrow).
  • Flexor Tendon Sheath Infection with three Kanavel's Signs: tenderness(T) along the flexor sheath, finger in a flexed position, and pain with passive extension.
    Infection with three Kanavel's Signs: tenderness(T) along the flexor sheath, finger in a flexed position, and pain with passive extension.
  • Surgical debridement and irrigation of thumb flexor sheath infection.
    Surgical debridement and irrigation of thumb flexor sheath infection.
Key Points
  • When surgically releasing a trigger thumb, the A-1 pulley is cut longitudinally.
  • During trigger thumb release the oblique pulley and A-2 pulleys should be preserved to limited bowstring of the FPL.
Grading of Muscle Strength
Exam References
Anatomic Abbreviations
Hand Surgery Resource Exams & Signs Library