LETTER TO THE EDITOR

Os vesalianum pedis misdiagnosedas fifth metatarsal avulsion fractureDear Editor,A 35-year-old man was seen in our outpatient ortho-paedic clinic for a scheduled follow up after he had beento the ED 1 week previously. He stated that he attendedthe ED after he had sprained his ankle, and ankle andfoot radiographs were taken. Thereafter, a below-kneeplaster cast was applied in the ED for a diagnosis offifth metatarsal avulsion fracture.emm_1221 426

Re-evaluation of the foot radigraphs taken at theinitial admission suggested an ossicle at the base of thefifth metatarsal, rather than a fracture. The ossicle wasseparated from the metatarsal by a radiolucent line ofconstant width, with a well-corticated edge (Fig. 1). Theplaster cast was therefore removed, and on physicalexamination there were tenderness and mild swelling ofthe anterior talofibular ligament and the sinus tarsi, butnone at the base of fifth metatarsal. Active and passiverange of motion of the ankle was nearly normal, and thepatient was able to weight bear and walk. The patientwas informed about the accessory ossicles around footand ankle including the os vesalianum pedis and wasdischarged with recommendations for management ofa simple ankle sprain.

Many skeletal variations exist around foot and ankleincluding accessory ossicles, sesamoid bones, biparti-tions and coalitions.1 Os vesalianum pedis is an uncom-mon accessory bone located proximal to the base of thefifth metatarsal. Its prevalence has been reported from0.1% to 0.4% of the population.2,3 It usually remainsasymptomatic and is recognized as an incidental radio-graphic finding. However, in a context of trauma, osvesalianum pedis can be misdiagnosed as a fifth meta-tarsal avulsion fracture as in our case.4 The clinical andradiological findings help differentiate these two dis-tinct entities.

Avulsion fracture of the base of the fifth metatarsalbone involves the insertion site of the peroneus brevistendon, which usually lie in a transverse plane. Theavulsed fragment is sharply marginated piece of bonethat lacks cortication at the fracture line.1,4 Clinically,there is oedema, tenderness and sometimes ecyhmosisaround the base of fifth metatarsal. Conversely, osvesalianum pedis is surrounded by bony cortex, and themargins are rounded. There might be articulation withadjacent cuboid bone.4

References

1. 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; 13: L164–77.

2. Coskun N, Yuksel M, Cevener M et al. Incidence of accessoryossicles and sesamoid bones in the feet: a radiographic study ofthe Turkish subjects. Surg. Radiol. Anat. 2009; 31: 19–24.

3. Tsuruta T, Shiokawa Y, Kato A et al. Radiological study of theaccessory skeletal elements in the foot and ankle. NipponSeikeigeka Gakkai Zasshi. 1981; 55: 357–70.

4. Boya H, Ozcan O, Tandogan R, Günal I, Araç S. Os vesalianumpedis. J. Am. Podiatr. Med. Assoc. 2005; 95: 583–5.

Ozkan Kose

Diyarbakir Education and Research Hospital, Orthopaedics

and Traumatology, Diyarbakir, Turkey

Figure 1. Lateral oblique radiograph of the foot. The whitearrow shows the os vesalianum pedis. Note the articular spacewith constant width and rounded margins of the bone.

doi: 10.1111/j.1742-6723.2009.01221.xEmergency Medicine Australasia (2009) 21, 426

© 2009 The AuthorJournal compilation © 2009 Australasian College for Emergency Medicine and Australasian Society for Emergency Medicine