Trigger Finger

Trigger Finger

Authors, Editors, Case Information Author: Laura Mattson, DO Affiliation: Mayo Clinic Jacksonville Co Author(s): Raul Rosario-Concepcion, MD Senior Editor: Raul Rosario-Concepcion, MD Clinical Vignette: 73yo right hand dominant female presenting for months of intermittent triggering and locking of the ring finger. Dynamic triggering of the digit is appreciated on exam with active flexion and extension. Type of Probe Used: 3-16 megahertz linear hockey-stick transducer #1 - Image Short axis view of the of the flexor digitorum superficialis and flexor digitorum profundus tendons at the level of the metacarpophalangeal joint. #2 - Image Short axis view of the of the flexor digitorum superficialis and flexor digitorum profundus tendons at the level of the metacarpophalangeal joint. The A1 pulley is seen in long axis and is indicated by the arrows; the maximal A1 pulley thickness measured 0.75mm (see measuring line for reference on where to measure). #3 - Image Long axis view of the flexor tendons, short axis view of the A1 pulley. #4 - Image Long axis view of the flexor digitorum superficialis and flexor digitorum profundus tendons at the level of the metacarpophalangeal joint. The A1 pulley is seen in short axis and is indicated by the arrows. #5 - Video View Video The flexor tendons of the fourth finger are scanned in short axis from mid palm to the level of the mid-shaft of the proximal phalanx. The flexor digitorum superficialis (FDS) begins volar to the flexor digitorum profundus (FDP) in the midpalm. Immediately distal to the MCPJ, the FDS tendon divides into two but remains volar to the FDP tendon. Thereafter, the FDS tendon slips begin to dive dorsal to the FDP tendon and finally (not pictured) attach to the middle phalanx just distal to the proximal interphalangeal joint. #6 - Video View Video The flexor tendons of the fourth finger are scanned in long axis at the level of the metacarpophalangeal joint (MCPJ). The A1 pulley lies just volar to the flexor tendons at the level of the MCPJ. A needle is seen traversing distal to proximal to penetrate the flexor tendon sheath, where a mixture of local anesthetic and corticosteroid is injected with excellent intra-sheath flow. #7 - Video View Video Dynamic imaging of the fourth digit is performed at the level of the metacarpophalangeal joint with passive flexion and extension. The flexor digitorum superficialis (volar) and flexor digitorum profundus (dorsal) tendons are seen in long axis. There is selective hypoechogenicity and thickening of the flexor digitorum superficialis tendon just distal to the region of the A1 pulley. The flexor digitorum profundus tendon appears normal. The flexor tendons have difficulty passing under the A1 pulley with dynamic motion. Interpretation Image Interpretation: The FDS and FDP tendons are intact from mid palm to distal insertion. The FDS tendon in particular is thickened and hypoechoic just distal to the A1 pulley. With dynamic imaging of flexion and extension of the digit, the tendons, in particular those of the FDS, have difficulty passing under the A1 pulley. The A1 pulley was thickened at 0.75mm. These findings are consistent with stenosing tenosynovitis. Additional dynamic imaging is seen of the therapeutic flexor tendon sheath corticosteroid injection, with excellent intra-sheath flow Teaching Pearl: Note that the maximal A1 pulley thickness can be measured and compared against a diagnostic cutoff value of 0.62mm, with anything above this being considered thickened. This dimension is best measured in a long axis view of the pulley (short axis view to the tendon). See the following reference. Spirig A, Juon B, Banz Y, Rieben R, Vögelin E. Correlation Between Sonographic and In Vivo Measurement of A1 Pulleys in Trigger Fingers. Ultrasound Med Biol. 2016 Jul;42(7):1482-90. doi: 10.1016/j.ultrasmedbio.2016.02.017. Epub 2016 Apr 26. PMID: 27126241.
NOTE: For more information, please contact the AMSSM, 4000 W. 114th Street, Suite 100, Leawood, KS 66211 (913) 327-1415.

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