Midfoot & forefoot

Published on 01/04/2015 by admin

Filed under Radiology

Last modified 01/04/2015

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17

Midfoot & forefoot

The standard radiographs

Protocols vary. In the UK a two view series is commonplace: AP and Oblique. Elsewhere, and in the USA, a three view series is common practice1,2: AP, Oblique, and a Lateral.

Abbreviations

AP, anterior-posterior; MT, metatarsal.

Normal anatomy

The bones of the midfoot form an arch. As a consequence several of the tarsal bones, specifically the three cuneiform bones and the bases of the metatarsals, overlap on both the AP and oblique projections. The individual bones can be separated from one another when the AP and oblique radiographs are examined as a complementary pair.

AP view

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Oblique view

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The cuneiform mortice and the Lisfranc joints

The base of the 2nd metatarsal is held in a mortice created by the three cuneiform bones. This mortice helps to prevent lateral slip of the bases of the metatarsals during weight bearing.

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Alignment of 2nd metatarsal and the intermediate cuneiform. May appear “notched”.

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Alignment of 3rd metatarsal and the lateral cuneiform. May appear “notched”.

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The common fractures

Metatarsals and phalanges

Very common. Some 35% of all foot fractures are metatarsal injuries3. In general, detection of a fracture involving any of the medial four metatarsals is easy.

As many as 70% of all metatarsal fractures involve the 5th metatarsal2.

Base of the 5th metatarsal

A fracture of the tuberosity represents an avulsion injury resulting from contraction of the peroneus brevis muscle and the pull of the plantar aponeurosis. It is caused by a plantar flexion–inversion injury.

A patient presenting with a twisted ankle: careful clinical examination of the base of this metatarsal will indicate when radiography of the foot, not the ankle, is necessary.

Potential pitfall: The normal unfused apophysis at the base of the 5th metatarsal is present in all children. It should not be misinterpreted as a fracture.

Helpful rules:

An avulsion fracture is situated either transverse or oblique to the long axis of the 5th metatarsal.

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