The Ankle

The Ankle, Talus and Calcaneum

Ottawa rules | Projections | Accessory ossicles | Mortise fractures
Weber classification | Salter-Harris classification | Toddler's fracture
Talus | Calcaneum

(click on images to enlarge)

Ottawa rules⁽¹⁾

Describe the requirements for plain x-rays within the clinical context of an ankle injury. They state that:

an ankle xray is required only if there is pain in the “malleolar zone” and any of these findings:
a foot x-ray is required only if there is pain in the “midfoot zone” and any of these findings:

Projections

AP mortise
This is obtained with internal rotation so that the fibula does not overlap the talus. This is important so that any joint space widening can be demonstrated. It also serves to clear the lateral joint space so that lateral talar dome fractures can be identified. Assess for any soft tissue swelling medially and laterally.

Lateral
Open collimation to include the calcaneum, 5th metatarsal base and dorsal surfaces of the talus and navicular (all common sites for avulsion fractures). Look for an anterior joint effusion, as this can be significant. An effusion is seen as an area of increased density that pushes out the adjacent fat plane.

Suboptimal positioning AP mortise
?Talar dome fracture. However, appearance is due to inadequate mortise view, and the lateral joint space not being clearly demonstrated:

Suboptimal positioning lateral
?Fracture lateral malleolus. However, appearance is due to inadequate lateral view and the medial and lateral malleoli not being superimposed:

Accessory ossicles – Normal variants

Unfused secondary ossification centres. These are well corticated osseous fragments that are located in characteristic places. Should not be misinterpreted as fractures; refer to Keats Atlas of Normal Variants if unsure. Some of the more common ossicles are:

Mortise fractures

As the ankle is a ring structure, if one displaced fracture is seen, another should be sought. The second injury may not be a fracture, but a ruptured ligament, which will be evident by widening of the joint. The main ligaments binding the ankle are:
- the medial and lateral collateral ligaments. These may rupture with or without an attached bony fragment:
- the interosseous ligament. The interosseous ligament may be assessed by ensuring that at approximately 1cm proximal to the tibial plafond, the distance between the tibia and fibula is not greater than 6mm. If greater than 6mm, a rupture should be suspected:
Full length tib & fib views are necessary if an apparently isolated fracture is seen at
- the medial malleolus (especially if displaced).
- the posterior malleolus (especially if displaced)
- or isolated widening of the medial joint space.
The second injury may be a fracture at the proximal fibula. This is referred to as a Maisonneuve injury:

$Maisonneuve fracture$ $Maisonneuve fracture$
If an apparently isolated fracture of the distal fibula is identified on the lateral view, search for a further fracture of the posterior malleolus which may be superimposed over the fibula fracture:

$fracture posterior malleolus, fracture fibula$ $fracture posterior malleolus, fracture fibula$

Weber Classification

A =	Lateral malleolar fracture below the level of the syndesmosis.
	Medial malleolar fracture; oblique (if present).
B =	Lateral malleolar fracture at the level of the syndesmosis, running proximally.
	Medial malleolar fracture; transverse. Or a tear of the ligament.
C =	Lateral malleolar fracture originating proximal to the joint line.
	Medial malleolar fracture; transverse. Or a tear of the ligament.

Additional to B or C may be a posterior malleolus fracture.

Salter-Harris Classification

Refers to fractures within the paediatric skeleton which involve the physeal growth plate. An injury to this area will cause a fracture to the weakest point, which is the cartilaginous growth plate, and spare the stronger joint capsule, ligaments and tendons. Depending on the involvement of the adjacent metaphysis and epiphysis, determines the classification:
- Salter-Harris Type I = Injury through the physeal growth plate only, usually with displacement. No involvement of the adjacent metaphysis or epiphysis:
- Salter-Harris Type II = Fracture extending through the physeal growth plate and adjacent metaphysis:
- Salter-Harris Type III = Fracture line running through the growth plate and adjacent epiphysis. This is intra-articular, and usually occurs at the site of ligamentous insertion:
- Salter-Harris Type IV = Triplane fracture involving the epiphysis, physeal plate and metaphysis. The fracture runs through the tibial epiphysis in the sagittal plane, horizontally through the physeal growth plate and through the posterior tibial metphysis in the coronal plane:
- Salter-Harris Type V = A compression fracture extending through the physeal growth plate. Often difficult to detect.
It is important to detect fractures through the physeal growth plate as, if missed and not treated, the growth plate may fuse prematurely causing deformity. As the classification increases from I to V, the frequency of injury decreases (type I and II common) but the severity of injury increases.

Toddler’s Fracture

Refers to a spiral fracture of the tibia. This is often undisplaced and is therefore difficult to detect; usually is only demonstrated on one projection. Occurs when the child (1-3years) twists and falls, with one leg fixed on the floor.

$toddlers fracture$ $toddlers fracture$

Talus

The talar dome should be scrutinised for a subtle indentation of the joint surface, or a small detached fragment. This is evidence of an osteochondral fracture. May be subtle, is often missed, but this injury is clinically significant:

$talar dome fracture$ $talar dome fracture$
Osteochondritis dissecans is characteristically seen within the talus. Osteochondritis dissecans refers to a sub-articular lucency with sclerotic margins, within which is seen an oval segment of bone (area of avascular necrosis). This will often give symptoms similar to the presence of a loose body, as there becomes a gradual separation of loose bone.
Avulsion off the dorsal surface of the head of the talus is common, as is the dorsal surface of the navicular, both identified on the lateral:
True sub-talar dislocation consists of dislocation of the talo-navicular and talo-calcaneum joints with navicular and calcaneum displaced with the foot. Frequently accompanied by fractures of the head/neck/dome of talus:

$subtalar fracture dislocation$ $subtalar fracture dislocation$

Calcaneum

Non-compressive avulsion fractures are common, particularly off the anterior process of the calcaneum, where the bifurcate ligament inserts. This may be identified on the lateral ankle or oblique foot projections:
A second common avulsion site is seen laterally on either the AP ankle or DP foot, at the insertion of the extensor digitorum brevis muscle:
Compressive fractures occur after a fall from a height. Subtle fractures may only be identified by assessing Boehler’s angle. This angle is measured by drawing a line from the highest point of the posterior tuberosity to the highest midpoint, and a 2nd line from the highest midpoint to the highest point of the anterior process. The angle, posteriorly, should be >30 degrees. If there is flattening of the bone due to a fracture, this angle will be decreased, to <30 degrees. Also assess the trabecular pattern for evidence if impaction (sclerosis):

$compression fracture calcaneum$