It's normal, but it hurts! Painful sesamoid and accessory bone syndromes of the foot.

It's normal, but it hurts! Painful sesamoid and accessory bone syndromes of the foot. Poster No.: P-0120 Congress: ESSR 2016 Type: Educational Poster Authors: A. C. Vieira, A. Vieira, R. Cunha; Porto/PT Keywords: Pathology, Normal variants, Education, Diagnostic procedure, MR, CT, Conventional radiography, Musculoskeletal bone, Bones, Anatomy DOI: 10.1594/essr2016/P-0120 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.essr.org Page 1 of 56

Learning objectives Recognize the normal bone structure of the foot with emphasis on sesamoids and accessory ossicles; Recognize their presence, prevalence and morphological variations; Radiography, CT and MRI of the normal anatomy and pathology of these bones. Background Sesamoids and accessory ossicles of the foot vary widely in their prevalence and morphology. There are almost 40 acessory ossicles described and the more common ones are: os peroneum; os subfibulare; os subtibiale; os tibiale externum; os trigonum; os calcaneus secundaris; os intermetatarseum; os supratalare; os supranaviculare and bipartite hallux sesamoid. Sesamoid bones are generally thought to form from a combination of biological and mechanical factors, beginning as cartilaginous nodules that then undergo endochondral ossification during early to late childhood. Accessory bones are supernumerary bones that commonly derive from unfused primary or secondary ossification centers and don't have a well-known function. Page 2 of 56

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Fig. 1: Acessory bones of the foot - AP (a), oblique (b) and lateral (c) - 1 Os trigonum, 2 os peroneum, 3 os naviculare, 4 os intermetatarseum, 5 os vesalianum 6 os supranaviculare, 7 os supratalare, 8 os talotibiale, 9 os calcaneus secundarium References: Insights Imaging (2013) 4:581-593 Table 1: Accessory and sesamoid bones: locations and prevalence References: Radiology, Hospital Espirito Santo de Evora - Porto/PT Page 4 of 56

Images for this section: Page 5 of 56

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Fig. 1: Acessory bones of the foot - AP (a), oblique (b) and lateral (c) - 1 Os trigonum, 2 os peroneum, 3 os naviculare, 4 os intermetatarseum, 5 os vesalianum 6 os supranaviculare, 7 os supratalare, 8 os talotibiale, 9 os calcaneus secundarium Table 1: Accessory and sesamoid bones: locations and prevalence Page 7 of 56

Imaging findings OR Procedure Details Accessory and sesamoid bones are normal structures of the foot that in normal conditions are asymptomatic. They are generally small, well-corticated and ovoid bones. Sesamoid bones may be bipartite or multipartite, and are located close to a bone or a joint. Awareness of the presence of sesamoids and accessory bones is helpful to not misdiagnose them as fractures. Although rare, symptomatic accessory and sesamoid bones may be associated with painful syndromes, due to various pathologies, including trauma, infection, inflammation and degeneration. Sesamoid Bones Sesamoids are osseous structures partially or totally embedded in a tendon and their function is to protect the tendon from injury by reducing friction. Normal anatomy and appearance There are three types of sesamoids: the hallucal sesamoids (most common and always present), the lesser metatarsal sesamoids and the interphalangeal joint sesamoid. The hallux sesamoids locate at the plantar aspect of the first metatarsal head. They are commonly two and the medial one frequently demonstrate bipartite variation. It is crucial to recognize this variation since it can be mistakenly recognized as a fracture. Page 8 of 56

Fig. 2: Anteroposterior and oblique views of the foot showing hallux sesamoids References: Department of Radiology, Hospital de São João, Porto, Portugal Page 9 of 56

The lesser metatarsal sesamoids locate at the plantar aspect of the second through fifth metatarsals and appear to be embedded in the joint capsule. They can also be multiple or multipartite. Fig. 3: Anteroposterior and oblique views of the foot showing a lesser fifth metatarsal sesamoid. References: Department of Radiology, Hospital de São João, Porto, Portugal Page 10 of 56

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Fig. 4: Anteroposterior radiograph of the foot showing lesser metatarsal sesamoids in a patient with a stress fracture (2nd metatarsal bone) References: Department of Radiology, Hospital de São João, Porto, Portugal The interphalangeal joint sesamoid locates at the plantar aspect of the interphalangeal joint of the first digit of the foot. It is embedded within the joint capsule and its presence can limit motion of this joint. Pathologic conditions Bipartite Hallux Sesamoid The hallux sesamoid bones develop from two ossification centers and they do not fuse at maturity, forming a bipartite sesamoid bone. The medial hallux sesamoid tends to be bipartite in morphology. This anatomical aspect is important once it should be differentiated from a sesamoid fracture. A true sesamoid bone fracture usually demonstrates a fragment that is not oval in shape and that don't have well corticated margins and the patient complains of an acute onset of pain and tenderness on direct palpation over the injured sesamoid bone. Page 13 of 56

Fig. 5: Anteroposterior and oblique views of the foot showing hallux sesamoids with the medial one demonstrating bipartite variation References: Department of Radiology, Hospital de São João, Porto, Portugal Page 14 of 56

Fig. 6: MRI. T1, Axial; Medial bipartite sesamoid References: Department of Radiology, Hospital de São João, Porto, Portugal Sesamoid bones syndrome Sesamoid bones syndrome refers to the deformation, cystic change and proliferation of the sesamoid bones induced by repetitive impingement on sesamoid bones. The impingement will increase pressure in the capsule of adjacent synovial joints, which ultimately results in inflammatory reaction that will lead to tenosynovitis of the flexor tendon, thickening and fibrosis of the joint capsule. The sesamoid bones syndrome can be well demonstrated by MRI, in which we can see bone marrow edema, soft tissue distention and tendon laceration, degenerative cystic change signals at the connection area between sesamoid bones and cartilages, as well as myotenositis of the long flexor muscle of the thumb and effusion within its tendon sheath. Page 15 of 56

Fig. 7: MRI Sagittal (T2 fat sat) and coronal (T1 and T2 fat sat); Sesamoiditis References: Department of Radiology, Hospital de São João, Porto, Portugal Infections Osteomyelitis affecting the sesamoids is most frequently secondary to direct extension from a soft tissue infection or from a septic joint. Page 16 of 56

Degenerative disease The hallucal sesamoids have a true articular joint with the metatarsal head so they are susceptible to osteoarthritis. Accessory ossicles Accessory bones result from a non-coalition of several ossification centers or development of extra and independent ossification centers. The most common accessory bones described in the foot are the os trigonum, os peroneum and os naviculare. Os trigonum Normal anatomy and appearance Os trigonum is located at the posterolateral aspect of the talus (resulting from a secondary ossification center that appears between the ages of 8 and 13) and can be seen on lateral radiographs of the foot. Usually it fuses with the talus forming "Stieda process" but when it remains unfused, it forms a synchondrosis with lateral tubercle of the talus. Its prevalence is variable ranging from 7 to 25 %. Page 17 of 56

Fig. 8: Lateral radiography of the foot showing an os trigonum References: department of Radiology, Hospital de São João, Porto, Portugal Page 18 of 56

Fig. 9: CT, Sagittal plane demonstrating the normal appearance of os trigonum References: Department of Radiology, Hospital de São João, Porto, Portugal Fig. 10: MRI, Sagittal T1; Os trigonum normal appearance References: Department of Radiology, Hospital de São João, Porto, Portugal Pathologic conditions Page 19 of 56

The symptomatic os trigonum may result from an acute or chronic injury and patient always refers a pain with mild swelling of the posterior ankle that is accentuated by resisted plantar flexion or dosiflexion of the great toe. An acute injury may be caused by trauma and can result in a os trigonum fracture, although this is a extremely rare condition. On the other hand, the chronic injury causing a posterior ankle impingement syndrome is more common and frequently results from excessive plantar flexion of the foot. So it is easy to comprehend that activities such as ballet can result in this syndrome. Fig. 11: MRI, T2 fat sat; Os trigonum syndrome References: Department of Radiology, Hospital de São João, Porto, Portugal Degenerative changes at the "os trigonum-talus articulation" can also occur resulting in synchondrosis, local synovitis, flexor hallucis longus tenosynovitis (as the tendon for the flexor hallucis longus sits medial to the os trigonum in the sulcus between the medial tubercle and the larger lateral tubercle) or intra-articular loose bodies. Os Peroneum Normal anatomy and appearance Page 20 of 56

The os peroneum is located at the cuboid tunnel adjacente to the calcaneocuboid joint and is embedded within the peroneus longus tendon. It can be best seen in oblique radiographs of the foot and in 30% of the cases it is bipartite. Page 21 of 56

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Fig. 12: Oblique x-ray showing an os peroneum References: department of Radiology, Hospital de São João, Porto, Portugal Pathologic conditions The os peroneum can be involved in painful syndromes as it locates within the peroneus longus tendon. A tear in this tendon results in lateral pain and tenderness along its course with displacement of the ossicle. Occasionally, os peroneum can subject to fracture or diastasis of a bipartite os peroneum. These fractures are particularly difficult to differentiate from bipartite sesamoids and a radiograph made with traction of the peroneus longus tendon can be helpful as it demonstrate diastasis and proximal migration of the fragment. Accessory navicular Normal anatomy and appearance The accessory navicular (or tibiale externum) bone is located at the posteromedial aspect of the foot adjacent to the posteromedial tuberosity of the navicular bone and is one of the most prevalent accessory bones (4-21%). It is best seen on anterioposterior radiographs of the foot. Page 23 of 56

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Fig. 13: Ankle x-ray showing an accessory navicular bone References: Department of Radiology, Hospital de São João, Porto, Portugal Accessory navicular bone can be divided in three types: Type I - Is considered to be a sesamoid bone located at the distal posterior tibial tendon Type II - The most common one, locates adjacent to the navicular bone and results from an aufused accessory ossification centre and have a synchondrosis to the navicular tuberosity Type III - Is the result of a fused type II accessory navicular bone that results in a prominent tuberosity Fig. 14: MRI, Coronal (T1) and axial (T2); Accessory navicular bone (incidental bone cyst on the right talus) References: department of Radiology, Hospital de São João, Porto, Portugal Pathologic conditions Painful accessory navicular is most commonly seen with the type II variant. It is thought that biomechanical irritation can be the source of the pain with shoe irritation been directly implicated. This irritation can lead to disruption of the synchondrosis, posterior tibial Page 25 of 56

tenosynovitis of tibialis posterior or even osteonecrosis. The tibialis posterior tendon often inserts with a broad attachment into this ossicle. Fig. 15: MRI, Axial T1 and T2 fat sat; symptomatic accessory navicular bone References: Department of Radiology, Hospital de São João, Porto, Portugal On MRI we can see an abnormal signal within the ossicle, in the synchondrosis and navicular tubercle, within the adjacent soft tissues and in the posterior tibial tendon. Os intermetatarseum Normal anatomy and appearance Page 26 of 56

The os intermetatarseum is located at the intermetatarsal space of the first and second metatarsals and is best seen on an anteroposterior radiograph of the foot. A very important differential diagnosis has to be made between a normal os intermetatarseum and a Lisfranc injury with fracture of the second metatarsal as the location of these two entities are similar, but treatment and prognoses are different. Pathologic conditions A painful syndrome of the os intermetataeseum is a rare condition and can result from the compression of the superficial or deep peroneal nerve by this ossicle. The patient complains of dorsal foot pain and numbness at the dorsum of the foot that is exacerbated by standing or jumping, and tenderness to palpation at the first intermetatarsal interspace. Os vesalianum Normal anatomy and appearance The os vesalium is located at the base of the fifth metatarsal and is embedded in the peroneus brevis tendon and may articulate with cuboid. It is rare and best seen in oblique radiographs of the foot. As in the anterior ossicle described is important to differentiate between a normal os vesalium and a fracture of the base of the fifth metatarsal. Pathologic conditions A painful syndrome can be seen when a tear of the peroneus brevis tendon occurs, similarly to that seen in os peroneum with peroneus longus tendon. Os supranaviculare Normal anatomy and appearance The os supranaviculare is rare in prevalence and is located at the dorsal margin of the talonavicular joint space and it can be best seen in lateral foot/ankle radiographs and should not be confused with avultion fracture. Page 27 of 56

Os supratalare Normal anatomy and appearance The os supratalare is located at the dorsal aspect of the talar neck and it can be best seen in lateral foot/ankle radiographs. This ossicle may be mistaken for flake fractures of the dorsum of the talus resulting from avulsion injuries but its rounded shape is the key for the differential diagnosis. Fig. 16: Sagital TC scan and lateral radiography of the foot showing an os supratalare References: Department of Radiology, Hospital de São João, Porto, Portugal Os talotibiale Normal anatomy and appearance The os talotibiale is located at the dorsal aspect of the talus adjacent to the talotibiale anterior part of the joint. Page 28 of 56

Fig. 17: MRI (Sagittal T2 fat sat) and CT (Sagittal); Os talotibiale References: department of Radiology, Hospital de São João, Porto, Portugal Pathologic conditions These three ossicles are rarely associated with painful syndromes and the most difficult part of their evaluation is their recognition itself. We have to be aware of their presence to differentiate them from avulsion fractures but the clues are the lack of a donor site, absent soft tissue swelling and their well corticated margins helping in this differential diagnosis. Os subfibulare Normal anatomy and appearance The os subfibulare is located at the tip of the lateral malleolus (0,2-2%). Pathologic conditions The principal consideration of this ossicle is to distinguish it from an acute avulsion fracture of the lateral malleolus. The os subfibulare is a rounded shaped ossicle with well corticated margins different from the fragment of a fracture that has a sharp fracture margin without sclerosis. Page 29 of 56

Os subtibiale Normal anatomy and appearance The os subtibiale is also rare (0,2-1%) and is located at the tip of the medial malleolus. Page 30 of 56

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Fig. 18: Coronal CT scan showing an os subtibiale References: Department of Radiology, Hospital de São João, Porto, Portugal Page 32 of 56

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Fig. 19: MRI, Coronal, PD fat sat; os subtibiale References: department of Radiology, Hospital de São João, Porto, Portugal Pathologic conditions Following an acute injury to the ankle the os subtibiale may be mistaken for an isolated medial malleolar avulsion fracture with MRI being once again the method of choice for this distinction. Os calcaneus secundarium Normal anatomy and appearance The os calcaneus secundarium is located at the anterior facet of the calcaneus positioned at the border of the calcaneus, the cuboid, the talar head and the tarsal navicular bone. It is best visualized on oblique foot radiographs or CT scans because of the overlying structures. Page 34 of 56

Fig. 20: Sagittal CT scan showing an os calcaneus secundarium References: Department of Radiology, Hospital de São João, Porto, Portugal Pathologic conditions The os calcaneus secundarium itself is rarely involved in painful syndromes however an important differential diagnosis have to be made between a normal os calcaneus secundarium and a fracture of the anterosuperior calcaneal process because they look similar on radiographs. MRI will be the method of choice for this differentiation because it can demonstrate the bone marrow edema of the anterosuperior calcaneal process when a fracture has occurred. Pathological conditions in sesamoids and accessory ossicles Page 35 of 56

As a summary, both sesamoid bones and accessory ossicles can be affected by trauma, infection, degenerative disease and osteonecrosis. Due to their locations in the foot some are more prone than others for different conditions. Trauma and fracture - Hallucal sesamoids and the os trigonum; Infection - Hallucal sesamoids (direct extension); Degenerative disease - Accessory navicular, os trigonum (accessory ossicles with synchondroses) and os peroneum (embedded within high-use tendons). Images for this section: Page 36 of 56

Fig. 2: Anteroposterior and oblique views of the foot showing hallux sesamoids Page 37 of 56

Fig. 3: Anteroposterior and oblique views of the foot showing a lesser fifth metatarsal sesamoid. Page 38 of 56

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Fig. 4: Anteroposterior radiograph of the foot showing lesser metatarsal sesamoids in a patient with a stress fracture (2nd metatarsal bone) Fig. 5: Anteroposterior and oblique views of the foot showing hallux sesamoids with the medial one demonstrating bipartite variation Page 40 of 56

Fig. 6: MRI. T1, Axial; Medial bipartite sesamoid Page 41 of 56

Fig. 7: MRI Sagittal (T2 fat sat) and coronal (T1 and T2 fat sat); Sesamoiditis Page 42 of 56

Fig. 8: Lateral radiography of the foot showing an os trigonum Fig. 9: CT, Sagittal plane demonstrating the normal appearance of os trigonum Page 43 of 56

Fig. 10: MRI, Sagittal T1; Os trigonum normal appearance Page 44 of 56

Fig. 11: MRI, T2 fat sat; Os trigonum syndrome Page 45 of 56

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Fig. 12: Oblique x-ray showing an os peroneum Page 47 of 56

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Fig. 13: Ankle x-ray showing an accessory navicular bone Fig. 14: MRI, Coronal (T1) and axial (T2); Accessory navicular bone (incidental bone cyst on the right talus) Page 49 of 56

Fig. 15: MRI, Axial T1 and T2 fat sat; symptomatic accessory navicular bone Fig. 16: Sagital TC scan and lateral radiography of the foot showing an os supratalare Page 50 of 56

Fig. 17: MRI (Sagittal T2 fat sat) and CT (Sagittal); Os talotibiale Page 51 of 56

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Fig. 18: Coronal CT scan showing an os subtibiale Page 53 of 56

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Fig. 19: MRI, Coronal, PD fat sat; os subtibiale Fig. 20: Sagittal CT scan showing an os calcaneus secundarium Page 55 of 56

Conclusion Awareness of the location, imaging characteristics, and associated pathologic entities is important for accurate image interpretation of alterations affecting accessory ossicles and sesamoid bones. References Robinson P. Impingement syndromes of the ankle. Eur Radiol. 2007;17 (12): 3056-65. Cerezal L, Abascal F, Canga A et-al. MR imaging of ankle impingement syndromes. AJR Am J Roentgenol. 2003;181 (2): 551-9. Lee JC, Calder JD, Healy JC (2008) Posterior impingement syndromes of the ankle. Semin Musculoskelet Radiol 12:154-169. Donovan A, Rosenberg ZS. MRI of ankle and lateral hindfoot impingement syndromes. AJR Am J Roentgenol. 2010;195 (3): 595-604. Keats TE, Anderson MW. Atlas of Normal Roentgen Variants That May Simulate Disease. Mosby Incorporated. (2007) Coskun N, Yuksel M, Cevener M et-al. Incidence of accessory ossicles and sesamoid bones in the feet: a radiographic study of the Turkish subjects. Surg Radiol Anat. 2009;31 (1): 19-24. Kalantari BN, Seeger LL, Motamedi K, Chow K. Accessory ossicles and sesamoid bones: Spectrum of pathology and imaging evaluation. Appl Radiol. 2007;36(10):28-37. Miller TT, Staron RB, Feldman F et-al. The symptomatic accessory tarsal navicular bone: assessment with MR imaging. Radiology. 1995;195 (3): 849-53. Personal Information Page 56 of 56