Reading Ankle Xrays

To reduce and splint ankles you have to understand the xrays and anatomy that you are working with. It is simple once you understand it, but until you do it is easy to get confused and make bad decisions with poor quality xrays.

• Verify correct patient and image date
  • I’ve seen scenarios where it would have saved hours of time to just look for old images in the medical record to see if a problem was chronic before just jumping in and trying to fix something that is chronic and can’t really be fixed with a reduction.
• Say what views your are looking at (AP, Mortise, Lateral)
  • If you aren’t sure, just say 3 views of a Left vs. Right ankle… for example
• Skeletally mature or immature?
• Look for obvious injuries and comment on them. Use the most straightforward and correct answer.
  • Don’t jump into the details right away
• Good example: AP, lateral and mortise view of a right ankle in a skeletally mature individual with an ankle fracture dislocation… (concise, accurate, to the point)
• Bad example: Looks like there is some comminution near the distal fibula, with small fracture fragments extending into the joint, oh and there is a small fracture near the medial mal, and then the talus is showing space on the medial side. (Don’t do this).
• After you have established the obvious. Go back and systematically go through the images in each view
• As always, it is helpful to start looking proximally and work your way distal

There are 3 main views in an ankle xray series, an AP, Mortise, and Lateral view, lets talk about them:

The AP view

(Radiopedia.org)

• This xray is shot with the 2nd toe in line with the xray beam. It will show you the ankle in a straight on view, the fibula is a more posterior structure, that is why there is much more overlap on an AP xray, rather than a Mortise view.
• Outline the tibia and fibula looking for fracture lines
• Look in medullary canals
• Overlap of fibula and tibia is >6mm
• Check medial clear space (medial clear space, < or equal to 4mm)
• Check tibiotalar joint congruity
  • Visualize ankle joint space and that there is equal clear space across the ankle joint on all sides, the medial, lateral and plafond.
  • In your mind, draw out the borders of the plafond and medial fibula (top white line), and draw out the bottom white line (body of the talus), the clear space between these lines should be relatively equal all the way across the joint.
  • This should be done on all views (AP, Mortise, Lateral)

(elentra.healthci.queensu.ca)

Mortise View

Ankle Mortise View (Figure from Schwartz 2008)

• Why is the Mortise view important?
  • Shows the tibio talar joint congruency
  • Shows you the syndesmosis
  • Better to evaluate reductions than on the AP view (The AP view will fool you into thinking that your talus is well reduced, when it really is subluxated)
• Check quality:
  • Medial and lateral malleoli are in profile, which means the anterior edge is perfectly lined up with the posterior edge, best seen on the medial malleolus
    • This means you can see from A to P in a clear line without any overlap.
  • Check syndesmosis
    • Tibia / fibula overlap >1mm on mortise view
  • • This line is straight down from the distal lateral tibia, and it should be in line with the lateral shoulder of the talus.
    • When the lateral talus is lined up with the distal lateral tibia, then this means the talus is well reduced, when the talus passes this line, then there is tibiotalar joint subluxation (or dislocation if the talus is out from under the plafond) Check that the tibio talar line (imaginary line) is intact.

    

• Here is another example, that shows the talus perfectly reduced, despite the distal fibula fracture

(Kwak talk)

• If the lateral talus passes this line as shown below this is an unstable ankle fracture with tibio talar joint subluxation

(Radiopaedia.org)

• See the difference side to side between the inner table of the medial mal on the AP view (on left) and Mortise view (on right)
• Also look at the difference between the tibia and fibula overlap (left AP ~6mm, right mortise ~1mm overlap)

Source: Radiopedia.org

• The Mortise view is very important, it shows the ankle joint with the incinsura lined up with the xray beam as shown below.

(Figure from Schwartz 2008)

• To obtain this view, the leg must be internally rotated by ~15 degrees, shown here:

  

• Internally rotating the leg brings the more posterior structure of the incinsura (or distal tibia fibular joint more in line with the xray beam)

Dime Sign

• Check the dime sign (this is more helpful when evaluating the length of your fibula during an ORIF in the operating room)
  • Dime sign = the fibula is out to length (not too short), an imaginary circle is drawn between the distal fibula and lateral talus that show the fibula is in a reasonable position
    • If the fibula is short from a fracture, then the distal fibula would not touch the “dime” and therefore you could say it was too short from its normal anatomy, as show in the image below.

Source: Journal of Foot and Ankle Surgery

• In the image below there is slight medial clear space widening, the dime sign is off slightly, but is relatively close to where the tip of the lateral malleolus lines up with the talus. If the fibula was short, it would not touch the top of the dime.

Lateral View

• Check image quality by looking at the fibula/tibia overlap and talar domes
  • Posterior fibula border is overlapping within a ⅓ of the posterior tibial border
  • Medial and lateral talar dome lines are lined up to create a perfect semicircle at the tibiofibular joint
    • In the image below, the left image is a poor quality image, fibula not within 1/3 of posterior tibia (blue lines), the talar domes are not lined up (red lines). The right image is corrected to the correct rotation and alignment with the xray beam.

      

      

(Wikiradiography.net)

Check in detail from proximal to distal

• Outline tibia, fibula, and medullary canals
• Review tibiotalar joint space, talus centered on tibia
• Review talus body and outline
• Talar-navicular joint
• Subtalar-joint
• Calcaneus body and outline
• Calcaneal Cuboid joint outline
• Soft tissue
  • Tibial talar joint capsule (blue outline)

    

  • Presence of an effusion can alert you to either blood in the joint for a subtle fracture, or even in the case of a septic arthritis
  • Example of an effusion, outlined in the image on the right:

    

  (Wikiradiography.net)

  • Achilles tendon (just posterior to Kagars fat pad)

    

  (Wikiradiography.net)

  • Kagars fat pad (Triangle just anterior to achilles tendon, posterior border of flexor hallucis tendon, superior to calcaneus)

    

    (Wikiradiography.net)

    Classification

    • • Fibula classification
      • Three types: A, B, and CDanis-Weber Classification (Or just “Weber Classification”) (Link)

      

      (Source)

    • Weber A
      • Fibula fracture distal to the tibiotalar joint
      • Usually stable if the only fracture
    • Weber B
      • Fibula fracture that exits into the tibiotalar joint
      • Variable stability, get a gravity valgus stress test to eval for medial clear space widening, if widened fixation required
    • Weber C
      • Fibula fracture proximal to the tibiotalar joint
      • Unstable fracture, commonly requires fixation
    • Lauge-Hansen Classification System (Link)
      • Remember: “SAD, SER, PAB, PER”
      • This system divides ankle fractures into 4 patterns based on the forces applied and the associated pattern.
      • Key point: Start by looking at the fibula to know the type
      • Supination Adduction (SAD)
        • Weber A fibula
        • Only ankle fracture with a varus failure and large vertical medial malleolus fragment
        • Commonly talus is dislocated anteriorly and has an associated tibial plafond fracture. (Get a CT)
        • Requires a valgus and posterior mold of the ankle

Mortise view: (Large Medial malleolus fragment with Weber A fibula)

Lateral view: (Anterior dislocation)

• Supination External Rotation (SER)
  • Spiral or oblique Weber B fibula fracture that extends into the syndesmosis
  • Varus molded splint required if unstable, get gravity stress xray if no medial clear space widening

    

• Pronation Abduction (PAB)
  • Weber C fibula, comminuted
  • Varus molded splint required if medial clear space widening

• Pronation External Rotation (PER)
  • Weber C fibula, commonly spiral
    • Key point: You get spiral fractures with rotational forces, so “external rotation” gives a spiral fracture, whereas abduction alone in a PAB fracture does not produce a spiral
  • Varus molded splint required if medial clear space widening

 

 

Operative Indications for Ankle Fractures

• Knowing the operative indications will help you counsel patients in the ED what to expect for future surgery and if it may be required
• Memorize this information below
• Emergencies:
  • Open fractures
  • Vascular compromise
  • Irreducible dislocations (Bosworth in case of fibula, or tibiotalar joint in case of tendon blocking reduction)
  • Skin tenting/ compromise
• Non emergent indications
  • Isolated medial or lateral malleolus fractures if:
    • any skin compromise
    • 3mm displacement (debated)
    • Any talar shift/subluxation on static or stress view (we get stress views on lateral mal fractures, no medial mal fractures)
  • Bimalleolar ankle fractures
  • Trimalleolar ankle fractures
  • Unstable bimalleolar equivalent ankle fractures (talar subluxation despite no medial malleolus fracture)
  • Unstable massoneuve type ankle fractures (high ankle sprains)
  • Posterior malleolus fractures criteria
    • 25% of articular surface
    • 2mm articular stepoff (depends on size of posterior mal)
    • Syndesmostic instability (the posterior syndesmotic ligaments attach to the posterior malleolus, so fix the posterior mal = fixing the syndesmosis)
    • Posterior subluxation of the talus

Examples:

Case 1: Previous left medial malleolus open reduction internal fixation (ORIF) with fracture malreduction and displacement. These screws are partially threaded screws, likely used as a “lag by design” technique.

On the left: Varus stress stress with displacement of the medial malleolus fracture. Also note the lateral malleolus fracture (distal fibula fracture.

What xrays are missing in this series? Lateral xray and AP views. The above xrays are closer to mortise views than AP views.

This fracture is similar to supination-adduction (SAD) type ankle fracture based on the Lauge-Hansen classification. this will have to be revised with a medial buttress plate with likely fibular fixation. This fracture would warrent a CT scan to evaluate the plafond. Without a lateral xray you can only call this a bi-malleolar fracture subluxation, or bi-mal ankle fracture subluxation.

Case 2 (link):

Mortise vew left ankle with medial clear space widening and sydesomosis injury (lateral talus is lateral to the lateral tibia/plafond. If you see this amount of syndesmotic injury without a fracture you have to order tibia/fibula xrays to evaluate for a higher fibula fracture.

You should also have AP and Lateral ankle xrays.

This fracture is called a Massoneuve ankle fracture.

AP and lateral tib/fib with a proximal fibula fracture.

AP and Lateral ankle fracture of a left Massoneuve fracture status post syndesmosis fixation with internal brace fixation (link).

80 year old female, ground level fall with right ankle pain:

What type of ankle fracture?

Answer: Right SER type ankle fracture or Right Weber B ankle fracture (not the full answer because you need to know if this type of fracture is stable or unstable)

What type of xray do you need to order to determine stability in a distal Weber B ankle fracture?

Answer: Gravity stress view

Here is the gravity stress view, is this ankle fracture stable or unstable?

Answer: There is medial clear space widening (>4mm), and the lateral talus is just barely lateral to the lateral tibial plafond. So the full most correct description of this ankle fracture would be: Unstable bi-mal equivalent ankle fracture (there is no medial malleolus ankle fracture, but the fact that the talus translates and there is medial clear space widening tells us that the syndesmosis and likely the deltoid ligament are disrupted make the fracture unstable.

Because it is unstable, plan in the ED would be to place this fracture in a varus molded splint under hematoma block (or sedation):

AP View:

 

Mortise View:

 

Lateral View: