Bipartite Sesamoid vs Fractured Sesamoid

Distinguishing a bipartite hallux sesamoid from a fractured hallux sesamoid can be challenging. While the clinician can easily tell by physical examination, the typical history of "rule out pain" that accompanies the majority of radiograph requisitions contains no helpful clues.

Several findings can help differentiate a bipartite hallux sesamoid from a fractured medial hallux sesamoid:

• Size: A medial sesamoid with a fracture is slightly larger than the lateral sesamoid, whereas a bipartite sesamoid is much larger.
• Cortication: Fractures have sharp, radiolucent, uncorticated lines, while bipartite sesamoids have two corticated fragments.
• Fit: The fragments of a fractured sesamoid often fit into each other, while the components of a bipartite sesamoid do not.

The case above shows a much larger bipartite medial hallux sesamoid with well-corticated margins. The two fragments do not fit into each other.

References

Mellado JM, Ramos A, Salvadó E, Camins A, Danús M, Saurí A. Accessory ossicles and sesamoid bones of the ankle and foot: imaging findings, clinical significance and differential diagnosis. Eur Radiol. 2003 Dec;13 Suppl 4:L164-77.