In this radiology lecture, we review the ultrasound appearance of trigger finger!

Key teaching points include:

Pulleys are fibrous retinacula on ventral finger that secure flexor tendons to phalanges preventing tendon displacement and bowstringing with finger flexion
Finger has 5 annular pulleys. Odd-numbered at joints, even-numbered at phalanges: A1, A3, A5 are located about the MCP, PIP, DIP joints, respectively. A2 is located at the proximal phalanx, and A4 at the middle phalanx
Cruciform pulleys lie between annular pulleys, but are not usually well-seen on ultrasound
Trigger finger, also known as stenosing tenosynovitis, is characterized by impaired flexor tendon movement due to thickened pulley leading to tendon constriction
Most common at A1 pulley, but can also occur at A2/A3 pulleys, palmar aponeurosis (A0) and wrist
Symptoms: Triggering/locking when flexed, painful snapping when extended, pain, joint stiffness
Most common in female patients, history of diabetes mellitus, and rheumatoid arthritis
Often idiopathic, can occur with repetitive microinjury (flexion-extension). Can also be post-traumatic or due to compressive mass/cyst
Tx: Splinting, NSAIDs, US-guided corticosteroid injection, surgical release
A1 pulley thickness cutoff = 0.62 mm*. Mean normal thickness = 0.5 mm, range with trigger finger 1.1-2.9 mm**. Comparison with asymptomatic side helpful
Additional findings: Pulley hyperemia, nodular tendon thickening (tendinosis) or tear, buckling of flexor tendon on dynamic imaging, “dark tendon” sign (anisotropic hypoechogenicity due to tendon constriction), synovial sheath effusion (acute), and peri-pulley cyst/cystic degeneration

References:

*Spirig A, Juon B, Banz Y, Rieben R, Vogelin E. Correlation between sonographic and in vivo measurement of A1 pulleys in trigger fingers. Ultrasound Med Biol 2016; 42:1482–1490.
**Guerini H, Pessis E, Theumann N, Le Quintrec JS, Campagna R, Chevrot A, Feydy A, Drapé JL. Sonographic appearance of trigger fingers. J Ultrasound Med. 2008 Oct;27(10):1407-13.
Bianchi S, Gitto S, Draghi F. Ultrasound Features of Trigger Finger: Review of the Literature. J Ultrasound Med. 2019 Dec;38(12):3141-3154.
Shohda E, Sheta RA. Misconceptions about trigger finger: a scoping review. Definition, pathophysiology, site of lesion, etiology. Trigger finger solving a maze. Adv Rheumatol. 2024 Jul 11;64(1):53.

To learn more about the Samsung RS85 Prestige ultrasound system, please visit: https://www.bostonimaging.com/rs85-prestige-ultrasound-system-4

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