ARRS 2022 Abstracts

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E1353. Symptomatic Accessory Ossicles of the Foot and Ankle
Authors
  1. Jee Moon; Temple University Hospital
  2. Ryan Graham; Temple University Hospital
  3. Daniel Kushner; Temple University Hospital
  4. Padmaja Jonnalagadda; Temple University Hospital
  5. Stephen Ling; Temple University Hospital
  6. Omer Awan; University of Maryland Medical Center
  7. Sayed Ali; Temple University Hospital
Background
Often noted as incidental findings by radiologists, accessory ossicles can be symptomatic, and therefore recognition is important. The primary goal of this exhibit is to provide an imaging review of symptomatic accessory ossicles of the foot and ankle, including the well-known os trigonum syndrome, painful os peroneum syndrome (POPS), os naviculare syndrome, great toe sesamoiditis, and the less well known os interphalangeus and os calcaneus secundarius syndromes. Equally as important is recognition of developmental variants that can be misinterpreted as pathology, e.g., the os intermetatarsum mimicking a Lisfranc fracture fragment, or the os subfibulare mimicking a fibula avulsion fracture, and these will be demonstrated. Plain radiographs, CT, MRI, gross anatomical images, and clinical pictures will be utilized to demonstrate the clinical and imaging characteristics of these various entities. Finally, the differential diagnosis as well as conservative and surgical management will be outlined.

Educational Goals / Teaching Points
This exhibit will demonstrate well known symptomatic ossicles of the ankle and foot and elaborate on less reported entities such as the os interphalangeus syndrome and os calcaneus secondarius syndrome; and percutaneous and surgical management can be curative.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Os naviculare syndrome is often caused by a type II accessory navicular, presenting with medial foot pain. T2 MRI demonstrates edema and fluid at the os naviculare synchondrosis; however, not all patients with os naviculare syndrome may show this finding. Type I and type III accessory naviculars are usually asymptomatic. POPS presents with lateral foot pain. Radiographs show the acute or chronic os peroneum fracture or diastasis. MRI findings show an os peroneum within the peroneus longus tendon often with increased T2 signal, consistent with edema, with peroneus longus tendinopathy or partial to complete tears often seen. The os calcaneus secundarius ossicle is located between the anteromedial calcaneus, cuboid, and anterior talus, which can be noted on radiographs but can be mistaken for an anterior calcaneal fracture, except the ossicle is larger than expected size for a fracture fragment. T2 MRI demonstrates increased signal signifying hypermobility of the fragment and osseous or soft tissue edema. Os interphalangeus syndrome is associated to a hallucal interphalangeal sesamoid, which may result in radiating pain to the first MTP joint. The sesamoid can uncommonly cause local mass effect, causing flexor hallucis longus tenosynovitis and bursitis. It can also cause failed reduction of an IP joint dislocation. Os trigonum syndrome is a clinical diagnosis, aided by radiography and MRI. Radiographs demonstrate the os trigonum between the posterior tibia and calcaneus. MRI shows increased T2 signal in flexor hallucis longus tendon. This may reflect tenosynovitis, capsular edema, or cystic change at the synchondrosis.

Conclusion
Accessory ossicles of the foot and ankle are common and mostly asymptomatic but can result in symptomatology that can be under-recognized and difficult to diagnose.