Figure 1. Anteroposterior radiograph of the left foot.
Figure 2. Oblique radiograph of the left foot.
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Figure 3. Lateral radiograph of the left foot.
A 21-year-old man presents to the office with pain in his left foot after he twisted his ankle 2 days ago. He was walking in the woods and stepped awkwardly on a rock, which caused the foot to buckle. He has had difficulty walking on the foot since. On physical examination, tenderness to palpation over the proximal fifth metatarsal of the left foot is noted. No edema or ecchymosis is observed over the lateral aspect of the foot. Anteroposterior, oblique, and lateral view radiographs are obtained (Figures 1, 2, and 3).
Which abnormality can be seen on this patient’s radiographs?
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The proximal fifth metatarsal is divided into 3 main sections: the proximal tubercle, the metaphyseal-diaphyseal junction, and the diaphysis. Fractures at the metaphyseal-diaphyseal junction are known as Jones fractures. A pseudo Jones fracture describes a fracture of the proximal tubercle. The lateral band of the plantar fascia and the peroneal brevis tendon attach to the proximal tubercle and can cause avulsion fractures with an inversion ankle injury. A fifth metatarsal apophysis may also be seen as a small sliver of bone on the lateral cortex of the fifth metatarsal, generally occurring in girls between the ages of 9 and 11 years and in boys aged 11 to 14 years. A proximal fifth metatarsal apophysis and accessory ossicles are often confused with small avulsion fractures. An os vesalianum is a rare accessory ossicle at the proximal fifth metatarsal and an attachment site of the peroneal brevis tendon. Os peroneum is more common and occurs at the lateral border of the cuboid and within the peroneal brevis tendon. Accessory ossicles have rounded, smooth edges whereas avulsion fractures have irregular scalloped edges. An os vesalianum is separated from the metatarsal by a radiolucent line of constant width and with smooth well-corticated edges, which helps distinguish the ossicle from an avulsion fracture. Fractures at the base of the fifth metatarsal are generally associated with edema and ecchymosis around the lateral foot.
Dagan Cloutier, MPAS, PA-C, practices in a multispecialty orthopedic group in the southern New Hampshire region and is editor-in-chief of the Journal of Orthopedics for Physician Assistants (JOPA).
1. Dameron TB Jr. Fractures and anatomical variations of the proximal portion of the fifth metatarsal. J Bone Joint Surg Am. 1975;57(6):788–792.
2. Kose O. Os vesalianum pedis misdiagnosed as fifth metatarsal avulsion fracture. Emerg Med Australas. 2009;21(5):426.