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.