Diagnostic accuracy of ankle x-rays: How often do we miss fractures? How can we improve?

Author: Jeremy Kim, MD (EM Resident Physician, Icahn School of Medicine at Mount Sinai) // Edited by: Alex Koyfman, MD (@EMHighAK, EM Attending Physician, UTSW / Parkland Memorial Hospital) & Justin Bright, MD (@JBright2021)

 Clinical Scenario

A 25-year-old male presents with a left ankle injury while playing basketball. There is swelling and ecchymosis diffusely with tenderness at the tip of the lateral malleolus. Should an x-ray be performed?

Background

Traumatic ankle pain is a common presenting problem to emergency departments. While sprains are the most common injuries (most common = anterior talofibular ligament), the patient still needs to be assessed for fracture.¹

Since its derivation and validation in 1992, the Ottawa ankle rules are the most frequently used clinical decision tool when considering to obtain ankle x-rays.²

Ottawa ankle rules: Ankle X-rays if pain in the malleolar zone PLUS one of the following:

1. Bony tenderness at “A”
2. Bony tenderness at “B”
3. Unable to bear weight both immediately and in the ED

How often are fractures missed?

When x-rays are ordered based on the Ottawa ankle rules, multiple studies have shown sensitivity at nearly 100% in adult populations while decreasing the number of x-rays ordered by 20-40%.^3,4 Similar sensitivity results are seen in pediatric populations, with near 100% sensitivity when categorizing Salter-Harris Type I as clinically insignificant due to low complication rate.⁵

One of the original multi-center validation studies for Ottawa ankle rules in 1995 revealed a 0.5% fracture miss rate, mostly because providers misused the clinical decision rule or in one case had difficulty assessing the grossly swollen ankle.³ However, at a similar rate, patients who underwent imaging had the x-rays initially read as negative.

What is the sensitivity of ankle x-rays?

The initial radiographic evaluation of the ankle involves three views (lateral, AP, and mortise). The mortise view is taken in 15-20 degrees of internal rotation with x-ray beams projecting perpendicular to the intermalleolar line. In an effort to save time and resources, some institutions use a two-view approach (lateral PLUS either AP or mortise), but this has a sensitivity of only 85-98%.^7,8 Overall, the diagnostic accuracy of ankle x-rays is unknown, but one study suggests that the incidence of occult fractures is about 1% and the degree of effusion correlated with the likelihood of occult fracture.⁹

In high-energy, poly-trauma, evaluation for ankle injuries may be more difficult due to the presence of distracting injuries or difficulty manipulating the extremity for adequate views on x-ray. In this scenario, when compared to multi-detector CT as a gold standard, sensitivity of x-rays can be as low as 87% for calcaneal fractures, 78% for talar fractures and 25-33% for midfoot fractures.¹⁰

Why do we miss fractures?

• Inadequate physical exam (eg. palpating incorrect areas and misusing the Ottawa ankle rules or gross swelling making palpation difficult)
• Unreliable patient (ie. altered, distracted, or intoxicated)
• Misinterpreting x-rays
• Occult fracture on x-rays, requiring further imaging

How can we improve?

• Thorough physical exam
  • Palpate posterior edge of distal 6 cm of both lateral and medial malleoli
  • Assess for associated proximal fibular fracture (Maisonneuve fracture): palpate the proximal fibula
  • Assess for syndesmotic ligament injury. Squeeze test (squeeze at mid-calf causes pain just proximal to ankle) or external rotation of foot (with tibia stabilized, causes pain at level of syndesmosis)¹¹
  • Assess for open fracture. Check for skin breakdown.
  • Neurovascular exam
• Review any imaging you order! You have the advantage of having examined the patient and have additional localization clues to detect fractures.
• Consider CT imaging if concerning mechanism or if needed for surgical considerations by orthopedic colleagues (eg. Pilon fracture)
• Instruct patient to follow-up within 1 week if no improvement in pain/ability to walk. Repeat x-rays at that time may reveal fracture
• Excellent resource on the approach to ankle x-rays: http://radiopaedia.org/articles/ankle-radiograph-an-approach

References / Further Reading

1. Tintinalli’s Emergency Medicine Manual. 7^th Ed. Chapter 175: Ankle and foot injuries.
2. Stiell I et al. Implementation of the Ottawa ankle rules. JAMA. Mar 1994; 271(11):827-32.
3. Stiell I et al, Multicentre Ankle Rule Study Group. Multicentre trial to introduce the Ottawa ankle rules for use of radiography in acute ankle injuries. BMJ. Sept 1995; 311:594-7.
4. Bachmann LM et al. Accuracy of Ottawa ankle rules to exclude fractures of the ankle and mid-foot: a systematic review. BMJ. Feb 2003; 326(7386): 417.
5. Myers A, Canty K, Nelson T. Are the Ottawa ankle rules helpful in ruling out the need for x-ray examination in children? Arch Dis Child. 2005; 90:1309-11.
6. Radiology masterclass: Trauma x-ray / Lower limb / ankle. <http://radiologymasterclass.co.uk/tutorials/musculoskeletal/x-ray_trauma_lower_limb/ankle_fracture_x-ray.html#top_second_img>
7. Brandser EA et al. Contribution of individual projects alone and in combination for radiographic detection of ankle fractures. Am J Roentgenol. Jun 2000; 174(6):1691-7.
8. De Smet AA, et al. Are oblique views needed for trauma radiography of the distal extremities? Am J Roentgenol. 1999; 172(6):1561-5.
9. Ho K et al. Using tomography to diagnose occult ankle fractures. Ann Emerg Med. May 1996; 27(5): 600-5.
10. Haapamaki VV, Kiuru MJ, Koskinen SK. Ankle and foot injuries: analysis of MDCT findings. Am J Roentgenol. Sep 2004; 183(3):615-22.
11. Busconi BD, Stevenson JH. Sports Medicine Consult: a problem-based approach to sports medicine for the primary care physician. Lippincott: 2009.
12. Berbaum KS et al. Impact of clinical history on radiographic detection of fractures: a comparison of radiologists and orthopedists. Am J Roentgenol. 1989; 153(6):1221-4.