Accessory ossicles of the ankle and foot Poster No.: C-2598 Congress: ECR 2013 Type: Educational Exhibit Authors: Á. Gómez Trujillo; Madrid/ES Keywords: Education and training, Education, MR, Digital radiography, Cone beam CT, Extremities, Bones, Anatomy DOI: 10.1594/ecr2013/C-2598 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. www.myesr.org Page 1 of 18
Learning objectives Literature has described many osseous anatomic variants and accessory ossicles in the ankle, some of which can mimic pathlogic conditions and others can actually be the source of the patient symptomatology. Knowing the most common variants and ossicles will allow the radiologist to avoid unnecessary explorations as well as misdiagnoses. Background Most of the accesory ossicles and sesamoid bones in the foot and ankle are asymptomatic. However, they can cause pain or suffer degenerative changes in response to overuse or trauma. Sesamoid bones: They are normally round or oval-shaped, and from 5 to 10 mm. They develop from their own ossification center. Some are completely or partially included in their own tendon. They usually locate next to oseus prominences or where their tendon changes direction or orientation, like the os peroneum and the os tibiale. Accessory bones: They are development variants, originated as secondary ossification centers which remain apart from the parent bone. They can be confused with avulsion fractures. The most frecuent are accesory scafoid and os trigonum. Os peroneum (figs 1-4): Located within the long peroneal tendon, next to the calcaneo-cuboid joint. Os tibiale: The posterior tibial tendon may contain within its fibres a sesamoid bone next to its insertion in the navicular tuberosity. Its important to remember that the fatty bone marrow inside the os tibiale will appear isointense with the fat around the tendon, which can lead to wrongly consider it as a tendon rupture. Accessory scaphoid (do not confuse with os tibiale) (Figs 5-7): Located in the medial margin of the scaphoid. It can cause a posterior tibial tendon tendinopathy or painful scafoid sindrome. There are 3 types of accessory scafoid: a) Type I: Small rounded ossicle inside the posterior tibial tendon. b) Type II : Larger triangular ossification center with a syncondrosis joint to the scafoid tuberosity. The ossification center measures approximately 9 to 12 mm Page 2 of 18
in size, and resides adjacent to the tubercle of the navicular bone. A residual cartilaginous synchondrosis joins the triangular type II ossicle approximately 1 to 2 mm medial and posterior to the navicular. The majority or entire tibialis posterior tendon inserts on the type II accessory ossicle. Type II accessory navicular is very commonly associated with medial foot pain. A valgus stress injury may fracture the synchondrosis, resulting in abnormal motion. Other times repetitive tendon contractions will cause strain in the syncondrosis, causing edema and pain. MRI is the most specific imaging modality for detecting the symptomatic accessory navicular, showing edema in the bone and soft tissues. c) Type III: cornuate navicular, is a prominent navicular tuberosity, connected to the medial aspect of the parent navicular by an osseous bridge. Os trigonum (Figs 8-10) : Next to the posterior process of the talus. It joins to the talus by a syncondrosis joint. It must not be considered fracture of free body. Os vesalium: Next to the proximal tuberosity of the fifth metatarsal and the os peroneum. Os supranavicular: Located in the dorsal surface ot the talo-scafoid joint. It can mimic a non consolidated avulsion fracture. Os subperoneal and subtibial (Figs 11 and 12): Under the peroneal and tibial malleolus. The os calcaneus secundarius: It is an accessory ossicle of the anterior facet of the calcaneus, which may be mistaken for a fracture of the anterior process. Although it is uncommon for an os calcaneus secundarius to cause symptoms, the ossicle can limit the range of motion in the subtalar joint, clinically resembling a calcaneonavicular coalition. Os sustentaculum tali: Between the anteromedial calcaneus process, the talus head, the cuboid and scaphoid bones. Images for this section: Page 3 of 18
Fig. 1: Lateral radiography of the right ankle showing os peroneum (red arrow). Page 4 of 18
Fig. 2: Sagital CT thick slice reconstruction of right ankle showing os peroneum (red arrow). Page 5 of 18
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Fig. 3: Right ankle lateral radiography showing os peroneum (red arrow). Fig. 4: Sagital T2 SPIR MRI showing simptomatic os peroneum (red circle). There is signal encrease in the long peroneus tendon. Page 7 of 18
Fig. 5: Axial T1 MRI image of the ankle with tipe II accessory scaphoid (red arrow). Page 8 of 18
Fig. 6: Coronal T1 MRI image of he ankle withtipe II accessory scaphoid (red circle). There is loss of signal in the accessory scaphoid due to bone edema. This patient was diagnosed with simptomatic accessory scaphoid due to the inflamatory changes seen in the bonem arrow adyacent to the syncondrosis. Page 9 of 18
Fig. 7: Coronal T2 SPIR MRI image of tipe II accessory scaphoid (red circle). There is signal increase in the accessory scaphoid due to bone marrow edema secondary to inflamatory changes adyacent to the syncondrosis. This patient was diagnosed with simptomatic accessory scaphoid. Page 10 of 18
Fig. 8: Sagital thick slice MPR reconstruction of richt ankle showing os trigonum (red circle). A longitudinal tibial fracture (red arrow) is also seen. Page 11 of 18
Fig. 9: Sagital 3D reconstruction of richt ankle showing os trigonum (red circle). A longitudinal tibial fracture (red arrow) is also seen. Page 12 of 18
Fig. 10: Sagital T1 MRI image showing os trigonum (red circle). Page 13 of 18
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Fig. 11: AP ankle radiography showing os subtibiale (red circle). Page 15 of 18
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Fig. 12: Coronal T1 image of the ankle with os superoneal (red circle). Page 17 of 18
Imaging findings OR Procedure details 1.5 Tesla MRI and X-Ray were used to perform the exams. Conclusion There are many accessory ossicles and anatomic oseous variants in the ankle and foot. Many of them can either mimic pathology or actually casue predispose to it. Xray and MRI are very usefull tools when aproaching these entities. Knowing the most common variants and ossicles will allow the radiologist to avoid unnecessary explorations as well as misdiagnoses. References 1. Mellado, J., Ramos, A. et all. Accessory ossicles and sesamoid bones of the ankle and foot: imaging findings, clinical significance and differential diagnosis. Eur Radiol. (2003); 13: L164-L177. 2. Mosel, LD., Kat, E. et all. Imaging of the symtomatic type II accessory navicular bone. Australasian Radiology (2004) 48; 267-271. 3. Keats TE (ed) Atlas of normal roentgen variants that may simulate disease, Mosby-Year Book, St. Louis, pp 615-704 4. Lawson JP. (1994)International Skeletal Society Lecture in honor of Howard D. Dorfman. Clinically significant radiologic anatomic variants of the skeleton. Am J Roentgenol 163:249-255 Personal Information Page 18 of 18