1. Os Trigonum Syndrome Tae Yong Moon, MD Pusan National University Yangsan Hospital Korea

2. Os Trigonum Syndrome thoward@gtowntimes.com Docpods.com Cerezal L. AJR 2003; 181:551-559 “Nut in a nutcracker”

3. Os trigonum syndrome pain Disruption of the cartilagenous synchondrosis between the os trigonum and the lateral tubercle of the posterior process secondary to repetitive microtrauma Compression of the os trigonum between the flexor hallucis longus and posterior talofibular ligament occurs in extreme ankle flexion Compression of the os trigonum between the calcaneus and talus occurs in the end range of plantarflexion

4. Posterior Ankle Impingement Anatomical structures resulting to posterior ankle impingement 1. Stieda’s process 2. Os trigonum 3. Fractured lateral tubercle 4. Posterior tibia malleolus 5. Calcified inflammatory tissue 6. Haglund deformity Cerezal L. AJR 2003; 181:551-559

5. Lateral Radiographs Os trigonum or lateral talar tubercle impinged between the posterior tibia malleolus and the calcaneal tuberosity

6. CT Osseous structure of the posterior ankle

7. Radionuclide Bone Scan Sensitive but not specific Gd DTPA T1 FS

8. MR Bone contusion with microtrabecular fracture, edema, and/or hemorrhage A fracture or pseudoarthrosis of the lateral talar tubercle or os trigonum Inflammatory changes in the posterior ankle soft tissues as the posterior synovial recess of the subtalar and tibiotalar joints and the FHL tendon sheath

9. 44M Left posterior ankle pain for walking PH; nonspecific Os trigonum syndrome Gd-T1 FS T2 FS Stenotic tenosynovitis of the FHL

10. 13M Left posterior ankle pain for 6 months PH; Soccer player during the middle school Recurrent ankle sprains Os trigonum syndrome Gd-T1 FST2 FS T1

11. Posterior Ankle Impingement 42/M CC; Chronic ankle pain Arthroscopy; synovitis Impression; PAI 096320189 T2 FST1Gd T1 FS

12. PAI with ganglion cyst 40/F CC; Painful bulging at the posterolateral aspect of the ankle in plantarflexion for about 1 year T2 FST1Gd T1 FS

13. Summary Os trigonum syndrome (OTS) is associated with disruption of the cartilaginous synchondrosis between the OT and the lateral tubercle. Anatomical structures resulting posterior ankle impingement (PAI) are OT, Stieda’s process, posterior tibia malleolus, lateral tubercle fracture, Haglund deformity, and inflammatory tissue. MR image is the best study to evaluate PAI including OTS.