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 #Posterior #Ankle #Impingement #Os #Trigonum #OsTrigonum #Syndrome #clinical #mri #clinical #Radiology #diagnosis #msk
