The peroneus brevis tendon inserts onto the 5th metatarsal base and the insertion site is at risk of avulsion fracture, associated with pulling off of the tendon. This is frequently seen in association with inversion injury at the ankle where the peroneus brevis contracts forcefully in a reflex attempt to stabilize the ankle as it inverts. It is sometimes termed a dancer’s fracture. The 5th metatarsal base should be included on the lateral ankle radiograph and carefully reviewed in cases of ankle inversion, with additional views of the foot obtained if necessary.

A second pattern of 5th metatarsal base fracture is seen occurring distal to the articulation between the 5th and 4th metatarsals as a result of an inversion injury to the foot and is susceptible to non-union.

Both these fractures tend to have a transverse configuration, a useful feature to distinguish them from an unfused proximal 5th metatarsal apophysis which has a longitudinal configuration. They can normally be diagnosed using conventional radiographs alone.

The Lisfranc joint is the tarsometatarsal articulation between the metatarsal bases and the tarsal bones (cuneiforms and cuboid). The joint is susceptible to trauma which can occur with minimal energy but lead to lifelong disability. The tarsometatarsal joints are stabilized by a series of tarsometarsal and intermetatarsal ligaments [7]. Importantly there is no intermetatarsal ligament between the 1st and 2nd metatarsal bases, the main stabilizer here being the Lisfranc ligament running from the medial cuneiform to the second metatarsal base. Disruption of this ligament complex is frequently associated with avulsion fractures which can be extremely subtle requiring CT for accurate diagnosis. If a bone avulsion is seen at any of the medial four TMT joints a dislocation should be suspected. Pure ligamentous injury does occur and is best detected with MRI although may be evident on the conventional radiograph in the form of joint subluxation or dislocation [7]. This may only be apparent on weight-bearing radiographs. In the normal situation on a DP radiograph the medial border of the 2nd metatarsal base should line up with the medial border of the intermediate cuneiform and, on a DP oblique radiograph, the same is true of the medial border of the 3rd metatarsal and the medial aspect of the lateral cuneiform.

Different patterns of Lisfranc dislocation may be seen depending on the injury mechanism.

Stress fractures are common in the foot. Calcaneal stress fractures may be confused with a diagnosis of plantar fasciitis and should always be considered in the differential diagnosis for heel pain. Typically they occur in the posterior calcaneus and have a vertical orientation appearing as a linear zone of sclerosis on the lateral radiograph.

Navicular stress fractures are a particularly challenging injury because of the difficulty of identifying them on conventional radiographs and the significant consequences to the patient if missed. They typically occur in the sagittal plane in an athletic population and will often require MRI and/or CT to make the diagnosis.

Stress and insufficiency fractures may be seen in the other tarsal bones and may only be evident on cross sectional imaging. However, the most common stress and insufficiency fractures in the foot occur in the metatarsals. These occur with prolonged repetitive activities such as running, walking and dancing; but may also result from altered biomechanics in the foot as a result of surgery or foot deformity. These fractures may involve any metatarsal and may be multiple. The fracture itself is rarely evident on conventional radiographs, the diagnosis usually being made by the detection of new bone formation at the fracture site. However, MRI may detect the stress reaction in the metatarsal as edema signal in the bone marrow and/or periosteum, before the fracture itself has occurred.

One or both hallux sesamoid bones may be fractured, the medial more commonly than the lateral. Since the normal hallux sesamoids may be bi- or even multi-partite distinction needs to be made between this normal variant and a fracture. Generally this can be done on the conventional radiograph where a bipartite sesamoid will have smooth corticated margins at the synchondrosis as opposed to the jagged, irregular fracture margins. A bipartite sesamoid will generally be larger than its neighboring non-bipartite sesamoid whereas the two components of a fractured sesamoid will make up a normal sized sesamoid. If diagnosis is difficult MRI or bone scintigraphy may be required [1].

The plantar fascia arises from the plantar surface of the calcaneus and comprises medial, central band and lateral bands. The central band itself is functionally the most important and covers flexor digitorum brevis. It divides into bands which pass towards each of the metatarsal heads. The lateral band covers abductor digiti minimi and has an insertion onto the 5th metatarsal base.

Plantar fasciitis is a common cause of heel pain and is more commonly seen in runners and dancers, but there is an association with obesity. On ultrasound plantar fasciitis is seen as thickening (>4 mm) of the plantar fascia in association with low reflective change (Fig. 3), while MRI demonstrates thickening with increased T1 and T2 signal. There may be associated adjacent soft tissue edema or bone edema in the calcaneus. In advanced disease partial or even full thickness tears may occur. The plantar fascia enthesis is also a common site of involvement in seronegative arthropathy and this should be considered in the differential diagnosis, especially if there is bone edema or erosion present.