Sesamoids and accessory ossicles of the foot: anatomical variability and related pathology

Insights into Imaging, Oct 2013

Sesamoids and accessory ossicles seen in the foot vary widely in their prevalence and appearance. Occasionally, these bones may be associated with painful syndromes, due to various pathologies, including trauma, infection, inflammation, degeneration and others. However, symptomatic accessory and sesamoid bones are rare, and search for additional pathology should be performed. Although the clinical significance of these osseous structures is probably minor, clinicians very commonly ask about these bones, which may originate an unnecessary work-up. Therefore, knowledge of their presence and morphological variations is important to prevent misinterpreting them as fractures—a common error. Finally, it may be very difficult to distinguish between incidental variants and truly symptomatic ones. Radiological studies provide insight regarding the presence and pathology involving these bones. This review describes an overview of the anatomy of sesamoids and accessory ossicles in the foot, and provides a pictorial review of their pathological conditions, including trauma, sesamoiditis, osteomyelitis, osteoarthritis and pain syndromes. Radiological studies including radiography, ultrasound, scintigraphy, computed tomography (CT) and magnetic resonance imaging (MRI) provide useful information which should be used in concert with clinical findings to guide patient management. Teaching points • Sesamoids and accessory ossicles seen in the foot vary widely in their prevalence and appearance. • Pathology of these bones includes trauma, sesamoiditis, infection, osteoarthritis and pain syndromes. • Radiography, ultrasound, scintigraphy, CT and MRI provide information regarding the pathology of these bones.

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Sesamoids and accessory ossicles of the foot: anatomical variability and related pathology

O. Kenechi Nwawka 0 1 Daichi Hayashi 0 1 Luis E. Diaz 0 1 Ajay R. Goud 0 1 William F. Arndt III 0 1 Frank W. Roemer 0 1 Nagina Malguria 0 1 Ali Guermazi 0 1 0 D. Hayashi Department of Radiology, Bridgeport Hospital, Yale University School of Medicine , Bridgeport, CT 06610, USA 1 F. W. Roemer Department of Radiology, University of Erlangen , Erlangen, Germany Sesamoids and accessory ossicles seen in the foot vary widely in their prevalence and appearance. Occasionally, these bones may be associated with painful syndromes, due to various pathologies, including trauma, infection, inflammation, degeneration and others. However, symptomatic accessory and sesamoid bones are rare, and search for additional pathology should be performed. Although the clinical significance of these osseous structures is probably minor, clinicians very commonly ask about these bones, which may originate an unnecessary work-up. Therefore, knowledge of their presence and morphological variations is important to prevent misinterpreting them as fracturesa common error. Finally, it may be very difficult to distinguish between incidental variants and truly symptomatic ones. Radiological studies provide insight regarding the presence and pathology involving these bones. This review describes an overview of the anatomy of sesamoids and accessory ossicles in the foot, and provides a pictorial review of their pathological conditions, including trauma, sesamoiditis, osteomyelitis, osteoarthritis and pain syndromes. Radiological studies including radiography, ultrasound, scintigraphy, computed tomography (CT) and magnetic resonance imaging (MRI) provide useful information which should be used in concert with clinical findings to guide patient management. Teaching points Sesamoids and accessory ossicles seen in the foot vary widely in their prevalence and appearance. Pathology of these bones includes trauma, sesamoiditis, infection, osteoarthritis and pain syndromes. Radiography, ultrasound, scintigraphy, CT and MRI provide information regarding the pathology of these bones. - Sesamoids are osseous structures partially or totally embedded in a tendon. Their function is to protect the tendon from injury by reducing friction. In contrast, accessory ossicles are supernumerary bones that commonly derive from unfused primary or secondary ossification centres [1]. They are thought to be normal variants with no definite known function. However, both sesamoids and accessory ossicles may be associated with pathological conditions. Sesamoids and accessory ossicles share several imaging characteristics: They are usually small, well-corticated, ovoid or nodular, may be bipartite or multipartite, and are found close to a bone or a joint. The presence of these osseous structures is usually incidental. Both sesamoids and accessory ossicles may be unilateral or bilateral, and are subject to significant morphological variations. Understandably, this may make the recognition of pathological conditions challenging. Although it is difficult to determine the symptomatic nature of these bones, imaging provides important diagnostic information to be considered in the clinical work-up. This article aims to review the normal anatomy of these bony structures, and to discuss their most common associated pathological conditions. The sesamoids seen in the foot include the hallucal sesamoids, lesser metatarsal sesamoids and interphalangeal joint sesamoid of the great toe (Fig. 1). Technically, os peroneum can be considered a sesamoid but it will be described in the ossicles section in this manuscript since it is anatomically classified as an accessory ossicle. A summary of the names of the sesamoids and accessory bones, their locations and prevalence is presented in Table 1. The hallucal sesamoids are always present at the plantar aspect of the first metatarsal head, and are a constant in humans. The Fig. 1 Sesamoids of the foot. AP radiograph depicting the sites of hallucal (1), interphalangeal joint (2 ) and lesser metatarsal (3 ) sesamoids AP and axial view radiographs of the foot best depict the hallucal sesamoids (Fig. 2). The medial sesamoid commonly shows bipartite variation [2]. Bipartite sesamoid fragments tend not to fit together perfectly, which aids differentiation from a fracture (Fig. 3) (Table 2). Associated pathology related to the hallucal sesamoids is not uncommon and in addition to fracture includes infection, arthritis and osteonecrosis [3]. Lesser metatarsal sesamoids Anatomically, sesamoids at the second through fifth metatarsals appear to be embedded in the plantar aspect of the joint capsule and may also be multiple or multipartite. The prevalence of sesamoids at the second through fourth metatarsals has been documented at 0.4 % at the second metatarsal, 0.2 % at the third, 0.1 % at the fourth, and up to 4.3 % at the fifth metatarsal [4]. If present, these sesamoids are best evaluated on AP and oblique radiographs of the foot (Fig. 4). Pathology (...truncated)


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O. Kenechi Nwawka, Daichi Hayashi, Luis E. Diaz, Ajay R. Goud, William F. Arndt III, Frank W. Roemer, Nagina Malguria, Ali Guermazi. Sesamoids and accessory ossicles of the foot: anatomical variability and related pathology, Insights into Imaging, 2013, pp. 581-593, Volume 4, Issue 5, DOI: 10.1007/s13244-013-0277-1