Posterior Ankle Impingement (Os Trigonum) Syndrome - MSK Radiology
Imaging Findings:
 • Os trigonum which has marrow signal alteration with T2-hyperintense and T1-hypointense signal; consistent with marrow edema/contusion.
 • Arrows showing posterolateral capsular thickening and fluid-signal consistent with synovitis.
 • "Edema-like" marrow signal of the posterolateral talus and calcaneus adjacent to the os trigonum.
Case description:
 • Usually presents with localized severe pain at the back of the ankle, worse upon plantar flexion.
 • Ballet dancer or other athletes with plantar flexion.
 • MRI: Posterolateral capsular thickening/synovitis; Predisposing factors such as Stieda process, os trigonum, abnormal morphology calcaneal tuberosity; Tenosynovitis flexor hallucis longus
Differential diagnosis for similar location of pain:
 • Posterior syndesmotic ligament tear: no impingement findings and torn ligament on MRI.
 • Achilles tendinopathy: thickening and abnormal signal of the achilles tendon.
 • Posterior talar dome osteochondral lesion: pain limits plantar flexion but no symptoms of impingement.

Dr. Donald von Borstel @DrvonBorstel

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