Sesamoids and accessory ossicles of the foot: anatomical variability and related pathology
O. Kenechi Nwawka
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1
Daichi Hayashi
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1
Luis E. Diaz
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Ajay R. Goud
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1
William F. Arndt III
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1
Frank W. Roemer
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Nagina Malguria
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Ali Guermazi
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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.
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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)