AP ankle radiographRadiology teaching during medical school is variable, ranging from informal teaching to required clerkships [1].​​ Many of us likely received an approach to a chest x-ray, but approaches to other studies may or may not have not been taught. We can do better! Enter EM:Rad, a series aimed at providing “just in time” approaches to commonly ordered radiology studies in the emergency department. When applicable, it will provide pertinent measurements specific to management, and offer a framework for when to get an additional view, if appropriate. We recently covered the elbow and wrist. Now: the ankle.

Learning Objectives

  1. Interpret traumatic ankle x-rays using a standard approach
  2. Identify clinical scenarios in which an additional view might improve pathology diagnosis

Why the ankle matters and the radiology rule of 2’s

The Ankle

  • 4% of all visits to the ED involve the ankle [2].
  • 20% of ankle injuries can have long-standing morbidity [3].
  • Does this patient even need an x-ray? Consider applying the Ottawa Ankle Rules.

Before we begin: Make sure to employ the rule of 2’s [4]

  • 2 views: One view is never enough.
  • 2 abnormalities: If you see one abnormality, look for another.
  • 2 joints: Image above and below (especially for forearm and leg).
  • 2 sides: If unsure regarding a potential pathologic finding, compare to another side.
  • 2 occasions: Always compare with old x-rays if available.
  • 2 visits: Bring patient back for repeat films.

An approach to the traumatic ankle x-ray

  1. Adequacy
  2. Bones
  3. Cartilage and ligaments
  4. Consider an additional view

1. Adequacy

  • Did you fully examine the entirety of the fibula, the base of the foot, or the midfoot? If not, consider imaging these areas if the patient has clinical or symptoms on a physical exam.
  • A standard ankle x-ray series consists of the AP, lateral and a 15 degree internal oblique (aka Mortise View) [2].
Example of a normal ankle series

Figure 1: Example of a normal ankle series. Case courtesy of Andrew Murphy, Radiopaedia.org

 

2. Bones

  • Tibia/Fibula (check on all views)
  • Talus (Talar dome highlighted) (check on all views)
  • Navicular bone (best seen on lateral view)
  • Calcaneus (Light Blue) (best seen on lateral view)
  • Cuboid (Yellow) (best seen on lateral view)
  • If seen on ankle series, base of 5th metatarsal (best seen on mortise or lateral)
normal anke x-ray series

Figure 2: Example of a normal ankle series. Case courtesy of Dr Andrew Murphy, Radiopaedia.org, annotated by Stephen Villa, MD

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3. Cartilage and ligaments

  • Pearl:  Physical examination maneuvers for the ankle should help diagnose potential ligamentous injuries.
  • Tibiofibular clear space: On AP view, this is the distance between the medial border of the fibula and lateral border of the peroneal incisura of the tibia 1cm above tibial plafond. Though >6 mm is often quoted in literature as abnormal, more recent literature demonstrates perhaps that an upper limit of 5.3 mm has a sensitivity of 82% and a specificity of 75% [5] for syndesmotic injury.
ankle x-ray syndesmosis

Figure 3: AP of patient with syndesmosis injury.  Note Tibiofibular clear space (black line). Case courtesy of Dr Henry Knipe, Radiopaedia.org

 

  • Medial clear space: On Mortise view, this is the widest distance between medial border of talus and lateral border of medial malleolus. Medial clear space > 4 mm or an increase of 2-3 mm compared to the contralateral side suggests syndesmosis disruption [5].
ankle x-ray mortise with medial clear space

Figure 4: Mortise view demonstrating medial clear space measurement. Patient does not have >4 mm widening. Case courtesy of Dr Andrew Murphy, Radiopaedia.org, annotated by Stephen Villa, MD.

  • Measure Bohler’s Angle:
    • On lateral view of ankle, this is the acute angle between two lines
      • Line 1: posterior tuberosity to posterior facet of calcaneus
      • Line 2: anterior process to posterior facet of calcaneus
    • A normal angle is 20-40 degrees; if the angle is <20 degrees, a calcaneus fracture should be strongly considered.
lateral ankle x-ray

Figure 5: Example of Bohler’s Angle measurement. Line 1: from posterior tuberosity (red solid arrow) to posterior facet (black arrow). Line 2: from anterior process (red dashed arrow) to posterior facet (black arrow). Case courtesy of Dr Henry Knipe, Radiopaedia.org

 

4. Consider an additional view

“Manual Stress” or “Gravity Stress” view

  • When: Weber B fracture pattern or concern for syndesmosis involvement
  • Why: Additional stress amplifies instability of joint, making it radiographically obvious.
    • Note: Recent studies indicate that stress views potentially may overestimate need for surgery [6, 7, 8], so keep this in mind when talking to the patient.
mortise view ankle x-ray with manual stress

Figure 6: Example of medial space widening on an manual stress view. Case courtesy of Dr Maulik S Patel, Radiopaedia.org

For further information, check out this CoreEM post about manual stress views.

Calcaneus View

  • When: High concern for calcaneus fracture
  • Why: Although this view exists, CT has better sensitivity and specificity for calcaneus fracture.

Learn More

References

  1. Schiller, P. et al. Radiology Education in Medical School and Residency. The views and needs of program directors. Academic Radiology, Vol 25, No 10, October 2018. PMID: 29748056
  2. Handel et al. Chapter 273. Ankle Injuries. In: Tintinalli’s Emergency Medicine. A Comprehensive Guide, 8th edition. New York: McGraw-Hill Education, 2016.
  3. Wedmore, I. et al. Emergency Department evaluation and management of foot and ankle pain. Emerg Med Clin N Am 33. Issue 2. May 2015. PMID: 25892727
  4. Chan, Otto. Introduction: ABCs and Rules of Two. ABC of Emergency Radiology, Third Edition. Edited by Otto Chan. 2013 John wiley & Sons, Ltd. Published 2013.
  5. Kellet, J. Diagnostic imaging of ankle syndesmosis injuries: A general review. Journal of Medical Imaging and Radiation Oncology. Volume 62. Issue 2. April 2018. PMID: 29399975
  6. Gougoulias, N. et al. When is a simple fracture of the lateral malleolus not so simple? Bone Joint J. Volume 99. No. 7. July 2017. PMID: 28663388
  7. Weber, M. et al. The use of weight-bearing radiographs to assess the stability of supination-external rotation fractures of the ankle. Arch Orthop Trauma Surg. Volume 130. No. 5. May 2010. PMID: 20082083
  8. Seidel, A. Weightbearing vs Gravity Stress Radiographs for Stability Evaluation of Supination-External Rotation Fractures of the Ankle. Foot and ankle International. Volume 38, No 7. May 2017. PMID: 28511569
Stephen Villa, MD

Stephen Villa, MD

Medical Education Fellow
Department of Emergency Medicine
University of California, Los Angeles