Midfoot & forefoot

Regularly overlooked injuries

▪ Fatigue fractures involving the 2nd or 3rd metatarsals.

▪ Avulsion fracture of the base of the 5th metatarsal—overlooked on ankle radiographs.

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 practice ¹^,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

Oblique view

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.

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

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

Analysis: the checklists

Analysis of the images will be influenced by the clinical findings such as the precise site of swelling, bruising, tenderness and pain.

The AP radiograph

Check:

1. Metatarsal and phalangeal shafts.

2. The Lisfranc joints. Always ask yourself … does the medial margin of the base of the 2nd metatarsal align with the medial margin of the cuneiform bone?

AP view.

Metatarsal shafts—normal. 2nd metatarsal aligns correctly with the intermediate cuneiform bone.

The oblique radiograph

Check:

1. Metatarsal shafts.

2. The Lisfranc joints. Does the medial margin of the base of the 3rd metatarsal align with the adjacent cuneiform bone?

3. The hindfoot bones and the hindfoot–midfoot articulations.

Oblique view.

Metatarsal shafts—normal. 3rd metatarsal aligns correctly with the lateral cuneiform bone.

The lateral radiograph

Check:

1. Base of the 5th metatarsal.

2. The hindfoot bones and the midfoot articulations.

Lateral view.

Base of 5th metatarsal—fracture (arrow).

Midfoot articulations—normal.

The common fractures

Metatarsals and phalanges

▪ Very common. Some 35% of all foot fractures are metatarsal injuries ³. 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 metatarsal ².

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.

Only gold members can continue reading. Log In or Register to continue