X-Ankle

Indication/Technique

The ankle x-ray is used primarily to demonstrate/exclude a fracture.

Depending on the request, various images can be made. A standard series includes an anteroposterior (AP) image, a Mortise image and a lateral image.
When calcaneal pathology is suspected, an additional image can be made in axial direction. 

AP image:

Pure AP image (fig. 1).

Figure 1. Technique and example of an AP image.

Mortise image:

This is an AP image where the ankle is turned 15°- 20° inward (= endorotation). This will prevent the fibula from overlapping the talus. This image allows for better free projection of the superior tarsal joint as compared to a pure AP image (fig. 2).

Figure 2. Technique and example of a Mortise image.

Lateral image:

Includes the full calcaneus. Ideally, the base of metatarsal I is also imaged (fig. 3).

Figure 3. Technique and image of a lateral ankle.

Axial calcaneal image:

The x-ray can be made in both standing and supine position, the foot is in dorsiflexion (fig. 4).
The x-ray beam passes the calcaneus.

Figure 4. Technique and image of an axial calcaneus in standing position.

Normal anatomy

The ankle consists of a fork formed by the tibia, the fibula and the talus. Together they form the superior tarsal joint (fig. 5). The primary movement taking place here is dorsiflexion (“toes towards you”) and plantar flexion (“toes away from you”).
The medial and lateral sides of the superior tarsal joint are formed by the talus/medial malleolus and the talus/lateral malleolus respectively.

 Figure 5. Pure AP image of a normal left ankle. MM = medial malleolus, LM = lateral malleolus.

As indicated previously, a Mortise image (= AP image in 15°- 20° endorotation) is made in particular to project the superior tarsal joint free of superimposition. Ankle endorotation reduces overlap of the lateral malleolus and the talus, bringing the lateral side of the superior tarsal joint better in view (fig. 6).

 Figure 6. Mortise image of a normal left ankle. MM = medial malleolus, LM = lateral malleolus.

The syndesmosis is a key stabilizer of the ankle and consists of (fig. 7):

  • the anterior tibiofibular ligament.
  • the posterior tibiofibular ligament.
  • the interosseous ligament.

Figure 7. Ligaments of the lateral malleolus (a/b), including the syndesmosis (= yellow ligaments).

Soft tissues (including ligaments) are not visible on x-ray. Nevertheless, ligament damage of the ankle may be observed indirectly (note: low sensitivity!). In a normal ankle, the joint space of the superior tarsal joint should be the same everywhere, a so-called congruent/symmetrical ankle fork. 
The distance between the distal tibia and fibula is important, also known as the tibiofibular clear space (fig. 8). It is measured at 10 mm cranial from the tibial plafond. When the distance between the distal tibia and fibula > 6 mm, be alert for a tear or rupture of the interosseous ligament.
Suspect medial ligament damage if the medial clear space is larger than the superior clear space. Important: damage to the medial collateral ligaments is frequently associated with syndesmosis damage.

Figure 8. The various clear spaces in the ankle. 

Lateral ankle image:

The malleoli are superimposed on the lateral image. The lateral malleolus (= fibula) continues on downward. 
The posterior malleolus is the posterior side of the distal tibia, also known as the malleolus tertius (fig. 9).

 Figure 9. Normal anatomy in lateral image of a left ankle. MT5 = metatarsal 5, mal. tertius = malleolus tertius (= posterior malleolus).

The calcaneus comprises four joint surfaces: one with the cuboid and 3 articulations (anterior, medial and posterior) with the talus (fig. 10).
The trabeculae protect the calcaneus against axial and shear forces (fig. 10b). The neutral zone contains the fewest trabeculae and is therefore the most vulnerable part of the calcaneus.

 Figure 10. Normal anatomy in a lateral image of the calcaneus (a) and the outlines of the trabeculae (b).

Axial calcaneal image:

In particular, the posterior 2/3rd segment of the calcaneus can be seen clearly (fig. 11).
The sustentaculum tali is a bony outcropping on the medial side of the calcaneus and supports articulation of the medial talus facet. Under the sustentaculum tali is the flexor hallucis longus tendon (= flexor tendon dig I).

 Figure 11. Normal anatomy in axial image of the calcaneus.

Accessory ossicles:

The ankle/foot contains many different accessory ossicles.  
These small ossal structures may be mistaken for an (avulsion) fracture. An accessory ossification center is smooth and rounded, as opposed to a fracture where the fragment is vague and irregular. 
In addition, the exact pain location must be ascertained; accessory ossicles generally do not induce pain symptoms.

Below is an outline of a number of common accessory ossicles of the ankle (fig. 12). Figure 13 shows an example of an accessory ossicle.

Figure 12. Common accessory ossicles of the ankle.

 Figure 13. Accessory os subfibulare. MM = medial malleolus, LM = lateral malleolus.

Checklist

The following points may be used as a guide to assess an ankle x-ray (some terms are explained in more detail in the Pathology section).

General:

  1. Technique: has everything been imaged correctly; is it suitable for evaluation?
  2. Soft tissues: swelling? skin intact? Other: includes foreign body or atherosclerosis?
  3. Bone mineral density? 
  4. Position of ankle fork? Cortical interruptions?  
  5. Joint articulation: osteoarthritis? luxation?
  6. If a calcaneal fracture is suspected: interruptions of the trabeculae? Böhler's angle?
  7. Accessory ossicles? Normal epiphyseal plates?
  8. Abnormalities outside the ankle joint?

Specific to a distal fibular fracture:

  1. Determine the level versus the syndesmosis. 
  2. Is there a fracture of the medial malleolus and/or posterior malleolus (= tertiary)? 
  3. Abnormal clear spaces? 

 

Pathology

 

  • Ankle fracture
  • Maisonneuve fracture
  • Calcaneal fracture
  • Talar fracture
  • Talar luxation
  • Osteoarthritis

Ankle fracture

The ankle is a ring structure consisting of the tibia, fibula and the talus. They are connected by 3 ligaments (the medial/lateral collateral ligaments and the interosseous ligament) As in each ring structure, one break will cause another break somewhere in the ring. The second break can be a fracture or ligament damage (= sprain/tear/rupture)  For this reason, diagnosing one ankle fracture should always prompt an active search for a second fracture.  The combination of fracture and ligament damage complicates assessment, as ligament damage is not directly visible on x-ray. Ligament damage may be inferred by an abnormal configuration of the ankle fork. 

The syndesmosis consists of the anterior/posterior tibiofibular ligament and the interosseous ligament (fig. 15).

Figure 15. Ligaments of the lateral malleolus, including the syndesmosis (= yellow ligaments).

The Weber classification and the Lauge-Hansen classification are commonly used in ankle fractures. 

  • Weber classification:

The subclassification is made based on the level of the fibular fracture in relation to the syndesmosis and the horizontal tibiotalar joint (fig. 16).

Figure 16. Weber classification.

Advantage:

  • Simple classification.
  • Easy application in practice.

Disadvantage:

  • Only describes the lateral malleolus.
  • Limitations in complex ankle fractures.
  • Syndesmosis damage may be underestimated.

Characteristics of Weber A:

  • Fibular fracture under the level of the syndesmosis (fig. 17).
  • Syndesmosis is intact.
  • Generally stable.

 Figure 17. Weber A fracture. 

Characteristics of Weber B:

  • Fibular fracture at the level of the syndesmosis (fig. 18).
  • Tibiofibular syndesmosis is intact/partial rupture.
  • NO widening of the tibiofibular joint.
  • Stable/unstable.

 Figure 18. Weber B fracture.

Characteristics of Weber C:

  • Fibular fracture above the syndesmosis (fig. 19).
  • Rupture of tibiofibular syndesmosis.
  • Unstable.

 Figure 19. Weber C fracture.

  • Lauge-Hansen classification: 

Describes the mechanism of the ankle fracture and is subdivided into 3 groups (supination-adduction, supination-exorotation and pronation-exorotation).

Advantage:

  • Provides insight into the trauma mechanism.
  • Affected structures (ossal & ligamentous) can be predicted. 
  • Better predictor of damage to the syndesmosis (versus the Weber classification).

Disadvantage:

  • More complicated than the Weber classification.

Supination-adduction: 
Mechanism (fig. 20): 

  • Foot in supination position (= foot turned inward).
  • Adduction force on the talus.

In practice, the mechanism is often referred to with the term “inversion trauma”.
Note: this trauma mechanism is also seen in Weber A fractures.

The ligaments at the lateral side of the ankle are exposed to high stress and an (horizontal) avulsion fracture develops (stage I). If the force is high enough, the medial malleolus  can be “pushed away” as it were (= vertical fracture) by the rotating talus (stage II) (fig. 20). A stage II is considered an unstable ankle fracture.

Figure 20. Trauma mechanism of supination-adduction according to Lauge-Hansen.

Below is an example of a supination-adduction fracture (fig. 21).

 Figure 21. Stage I supination-adduction fracture.

Supination-exorotation: 
Mechanism (fig. 22):

  • Foot in supination position (= foot turned inward)
  • Exorotation force on the talus.

Note: this trauma mechanism is also seen in Weber B fractures.

Figure 22. Trauma mechanism of supination-exorotation according to Lauge-Hansen.

The exorotation movement produces a direction of force at the front of the ankle (stage I). The force then rotates anteriorly around the ankle to lateral (stage II) and continues behind the ankle (stage III), ending at the medial side of the ankle. The exorotation movement of the talus will cause the (fixated) lateral malleolus to break.
Outline of stages (fig. 23):

  1. Stage I: rupture of anterior tibiofibular ligament (= anterior fork ligament)
  2. Stage II: oblique or spiral fracture of lateral malleolus
  3. Stage III: rupture of posterior tibiofibular ligament (= posterior fork ligament) and/or fracture of malleolus tertius
  4. Stage IV: rupture of medial collateral ligament and/or fracture of medial malleolus

Figure 23. Various stages (I - IV) of trauma mechanism of supination-exorotation according to Lauge-Hansen. Note: in the 2 most severe forms (= stage III and IV), there is ligament damage and/or fracture.
PTFL = posterior tibiofibular ligament. ATFL = anterior tibiofibular ligament.

Below is an example of a supination-exorotation trauma. The fracture line of the distal fibula continues to the level of the horizontal tibiotalar joint (stage II). There is also a tertius fracture (III). In view of the widened medial clear space, this is a rupture of the medial collateral ligaments (stage IV).

 Figure 24. Supination-exorotation fracture (stage IV). Note the widened medial clear space (red arrow); rupture of medial collateral ligaments.

The ankle forte is unstable and the distal fibular fracture is fixated using plate osteosynthesis (fig. 25). The postoperative ankle fork is once again symmetrical.

 Figure 25. Fixation of distal fibula using plate osteosynthesis.

Pronation-exorotation:
Mechanism (fig. 26):

  • Foot in pronation position (= foot turned outward).
  • Exorotation force on the talus.

Note: this trauma mechanism is also seen in Weber C fractures.

Figure 26. Trauma mechanism of pronation-exorotation according to Lauge-Hansen.

The direction of force rotates around the ankle. The damage starts at the medial side, turns anteriorly along the ankle to lateral, ending at the posterior side.

The ligaments at the medial side of the ankle are exposed to high stress and an avulsion fracture develops (stage I). The talus will continue to exorotate and will no longer be checked by the medial ligaments, causing the talus to push away the fibula.

Outline of stages (fig. 27):

  1. Stage I: rupture of medial collateral ligament and/or fracture of medial malleolus.
  2. Stage II: rupture of anterior tibiofibular ligament (= anterior fork ligament).
  3. Stage III: rupture of interosseous membrane + high fibular fracture. 
  4. Stage IV:  rupture of posterior tibiofibular ligament (= posterior fork ligament) and/or fracture of malleolus tertius.

Figure 27. Various stages (I - IV) of trauma mechanism of pronation-exorotation according to Lauge-Hansen. Note: in the most severe form (= stage IV), there is ligament damage and/or fracture. 
PTFL = posterior tibiofibular ligament. ATFL = anterior tibiofibular ligament.

Below is an example of a pronation-exorotation fracture (fig. 28).

 Figure 28. AP (a) and lateral (b) ankle image. High fibular fracture and a tertius fracture. In view of marked medial soft tissue swelling, there will also be ligament damage (or an occult fracture). This is a stage IV pronation-exorotation fracture.

Comments: 

  • When confronted with ankle fractures, remember that fractures may resume their anatomical positions immediately after the trauma; a fracture can easily be overlooked. 
    Example: an isolated tertius fracture is very rare. Keep in mind that a tertius fracture can be stage III (supination-exorotation) or stage IV (pronation-exorotation) and that damage may be more extensive than initially visible on the image (both ossal and ligamentous).
  • An x-ray does not exclude ligament damage. Although the ankle fork in a Weber B/C fracture is initially symmetrical, there may still be a ligament rupture. In that case the ankle is unstable and may dislocate.  

 

  • Ankle fracture
  • Maisonneuve fracture
  • Calcaneal fracture
  • Talar fracture
  • Talar luxation
  • Osteoarthritis

Maisonneuve fracture

The described ring theory of the ankle fork extends to the knee. As stated previously, the fibular fracture is always located above the syndesmosis in a Weber C type. This can be immediately above the ankle fork, but also more towards proximal.
In a Weber C ankle fracture therefore, a fracture may develop at the proximal fibula, also termed a Maisonneuve fracture (fig. 29)  
in other words, a Maisonneuve fracture is actually a high Weber C fracture.

Figure 29 Maisonneuve fracture.

In Maisonneuve fracture, think of:

  • An isolated fracture of the medial malleolus associated with a widening of the medial joint space.
  • Isolated tertius fracture.
  • Painful at the level of the proximal fibula.

Below is an example of a tertius fracture. Initially, an isolated fracture is suspected. But upon closer evaluation, marked soft tissue swelling is noted at the level of the medial and lateral malleolus, and ligament damage is suspected.
It turned out the patient also experienced pain at the fibular head. An additional image reveals a proximal fibular fracture (fig. 31).
This is therefore not an isolated tertius fracture, but an unstable Weber C (stage IV pronation-exorotation) fracture.

 Figure 30. Tertius fracture on a lateral image of a right ankle (a). The Mortise image (b) reveals no fracture, but marked soft tissue swelling at the level of the malleoli. 

 Figure 31. Lateral image of proximal right upper leg. Proximal fibular fracture, this is a Maisonneuve fracture.

 

  • Ankle fracture
  • Maisonneuve fracture
  • Calcaneal fracture
  • Talar fracture
  • Talar luxation
  • Osteoarthritis

 

Calcaneal fracture

When a calcaneal fracture is suspected, both an axial and lateral image should be made.

A calcaneal fracture (also termed lover’s or Don Juan fracture) usually develops after a fall from height. The extent is easily underestimated, which is why an additional CT scan is frequently made in a comminuted fracture.
Bilateral calcaneal fracture is present in 10% of the cases.
In isolated cases, there may be a relatively simple rotation trauma, as in a fracture of the anterior process (fig. 32).

 Figure 32. Anterior process fracture of the calcaneus.

Sometimes calcaneal loss of height is the only indication of a fracture. Böhler's angle may help determine the loss of height. 
This angle is created by 2 lines (fig. 33):

  • Line from the posterior tuberosity towards the apex of the (posterior) subtalar joint.
  • Line from the anterior process towards the apex of the (posterior) subtalar joint.

 Figure 33. Böhler's angle.

A normal angle is about  28° - 40°.  Angles smaller than 28° suggest a fracture.

Another clue to a subtle fracture is an abnormal pattern of the trabeculae; a sclerotic line/density may be indicative of an impacted fracture. 
Tip: The neutral zone contains the fewest trabeculae and is the weakest part of the calcaneus (fig. 34). This area is therefore the most susceptible to a fracture.

Figure 34. Normal outline of the trabeculae of the calcaneus. 

Below is an example of a calcaneal fracture (fig. 35).

 Figure 35. Lateral and axial calcaneus image in an intra-articular comminuted calcaneal fracture.

Comment:  As a result of the high axial force, a calcaneal fracture is strongly associated with a fracture at the thoracic/lumbar level. You should therefore always examine the patient’s back and not hesitate to make a thoracic/lumbar x-ray.

  • Ankle fracture
  • Maisonneuve fracture
  • Calcaneal fracture
  • Talar fracture
  • Talar luxation
  • Osteoarthritis

 

Talar fracture

A talar fracture may develop as a result of a forced turning movement, forced dorsiflexion or axial compression force.
A talar fracture may be subclassified by location:

  • Corpus tali
  • Talar neck: is often overlooked, particularly when associated with only limited dislocation. Increased dislocation is associated with a high risk of avascular necrosis (note: most vascularization takes place via the talar neck).  
  • Talar dome (osteochondral fracture): this is a defect/irregularity at the medial or lateral side of the talar dome. In some cases, the fragment becomes dislodged in the joint (= free body).
  • Posterior: a fracture at the posterior side may be mistaken for an os trigonum and vice versa.

Three quarters of the fractures are in the neck and the corpus.
Below is an example of a subtle fracture of the talar neck (fig. 36).

 Figure 36. AP image: Subtle fracture line at the lateral side of the talus, in a person whose ankle had “doubled” when walking down the stairs.

 

  • Ankle fracture
  • Maisonneuve fracture
  • Calcaneal fracture
  • Talar fracture
  • Talar luxation
  • Osteoarthritis

 

Talar luxation

Talar luxation is rare. In view of the high risk of avascular necrosis, the fracture should be repositioned as soon as possible. 
Talar luxation may be subtle on a standard ankle series. The primary clue is abnormal talonavicular articulation (fig. 37). An additional foot image can also provide clarification (fig. 38).

 Figure 37. Lateral image (a) and AP image (b) with the talus luxated towards lateral. Note the abnormal articulation between the talus and the os naviculare (red arrows).

 Figure 38. The additional foot image clearly reveals abnormal talonavicular articulation; the talus is luxated towards lateral. There is also a talar fracture.

 

  • Ankle fracture
  • Maisonneuve fracture
  • Calcaneal fracture
  • Talar fracture
  • Talar luxation
  • Osteoarthritis

 

Osteoarthritis

Symptoms in osteoarthritis are diverse. Patients may complain about progressive load-dependent pain and/or reduced ankle function. 
The osteoarthritis may be primary with no obvious identifiable cause. Secondary osteoarthritis develops after e.g. a fracture.
Radiological characteristics of osteoarthritis (fig. 39):

  • Narrowing of the joint space (secondary to loss of cartilage).
  • Subchondral sclerosis (increased bone production secondary to increased pressure with cartilage loss).
  • Osteophyte formation (bone exostoses attempting to increase the joint surface).
  • Subchondral cysts (secondary to microfractures of the subchondral bone and pressure of the synovial fluid).

 Figure 39. Lateral image of a right ankle. Osteophyte formation, joint space narrowing and subchondral sclerosis as signs of osteoarthritis.

Footballer’s ankle:
(Professional) football players in particular make repetitive forced movements. This may give rise to cartilage damage. They typically develop in football players at the front of the tibia and the inner side of the medial malleolus. 
The osteophyte formation and chronic recurrent synovitis lead to painful and limited dorsiflexion of the ankle (impingement symptoms).

Sources

  • B.J. Manaster et al. The Requisites – Musculoskeletal Imaging (2007).
  • N. Raby et al. Accident & Emergency Radiology – A Survival Guide. (2005).
  • R.W.Bucholz Rockwood & Green’s Fracturen in Adults. (2006).
  • Prof.dr. J.A.N. Verhaar, dr. J.B.A. van Mourik. Orthopedie. (2008).
  • Simplified diagnostic algorithm for Lauge-Hansen classification of ankle fractures. Radiographics 2012 Foot Ankle Int. (2012).
  • Fractures of the Calcaneus: A Review with Emphasis on CT. Aditya Daftary, MB et al.Radiograpics (2005).
  • Correlation between radiological assessment of acute ankle fractures and syndesmotic injury on MRI. J. J. Hermans JJ et al.  Skeletal Radiol (2012).

 

Author

  • Annelies van der Plas, resident radiology LUMC

  • Prof. dr. J.L. Bloem, radiologist LUMC

24/01/2014 (translated 28/07/2016)

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