In the setting of trauma, sesamoid bone abnormalities consist of acute fracture, stress fracture, and dislocation. It is often difficult to differentiate a fractured hallucal sesamoid from a bipartite hallucal sesamoid (9). Imaging clues to differentiate a fractured single medial sesamoid from a bipartite medial hallucal sesamoid include: the fractured sesamoid is usually slightly larger than the lateral sesamoid while the bipartite sesamoid has a much larger medial sesamoid than lateral sesamoid; the fractured sesamoid shows a sharp, radiolucent, uncorticated line between the two fragments while the bipartite sesamoid has two corticated components; the fractured sesamoid fragments often fit together like pieces of a puzzle while the bipartite sesamoid has two components that do not fit together snugly; the fractured sesamoid will show increased uptake on a 99mTc-MDP bone scan while the bipartite sesamoid may not; and the recently fractured sesamoid may demonstrate bone marrow edema while the bipartite sesamoid may not 15 . Additional signs of a fractured sesamoid include bone displacement or soft tissue swelling.
9 Figure 9: Fracture of the medial sesamoid of the first metatarsophalangeal joint in a 49-year-old woman. Radiograph (top left) shows a fractured medial sesamoid (arrow) of the first metatarsophalangeal joint. Corresponding axial T1-weighted MR image (top right) demonstrates the fracture (arrow). Coronal T1-weighted (bottom left) and T2-weighted fat-suppressed (bottom right) MR images demonstrate marrow edema within the osseous fragments (arrowheads).
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