Calcaneofibular avulsion fracture

Case contributed by Dr Brian Gilcrease-Garcia

Presentation

Lateral ankle pain after tripping

Patient Data

Age: 55 years
Gender: Female
X-ray
  • focal soft tissue swelling overlying lateral ankle
  • small avulsion fracture fragment located in the fibular-calcaneal interval (only evident on AP view)

The patient placed an MR-compatible marker on skin overlying site of focal pain.

  • lateral compartment
    • anterior talofibular ligament (ATFL) severely attenuated and partially ruptured with fluid along talofibular gap, consistent with at least a grade 2 sprain
    • thickened and lax appearance of calcaneofibular ligament (coronal T2-FS images), which can be followed inferiorly from fibular tip to a tiny avulsed fracture fragment (axial and coronal T1).  Focal marrow edema and a matching tiny T1 hypointensity of the lateral calcaneus near the peroneal tubercle indicate the donor site
    • posterior talofibular and syndesmotic ligaments intact
  • small ankle effusion
  • marrow edema along anterior cuboid and talus, although without discrete T1 hypointensity. Findings most consistent with bone contusions
Annotated image
  1. subtle calcaneal avulsion fracture fragment (yellow circle)
  2. approximate location of calcaneofibular ligament (orange dotted line), calcaneal fracture donor site (blue asterisk)
  3. avulsed fracture fragment (yellow circle), calcaneal donor site (blue arrow)
  4. thickened, frayed distal calcaneofibular ligament (orange arrow)

Case Discussion

Lateral ankle injuries are extremely common, most commonly injury to anterior talofibular (ATFL) and calcaneofibular ligaments (CFL). High grade "sprain" injuries consist of either intrasubstance ligament rupture, or small avulsion fractures at the ligamentous insertions. It is hypothesized that the latter are more common at slower injury velocity and of a bipolar age distribution (more common in young and elderly patients) 1.

Typically, avulsion injuries involving the ATFL and CFL result in fracture of the fibular tip. This case is unusual because it is the calcaneal attachment of the CFL which is avulsed.

A few specific points:

  • small avulsion fractures may be quite subtle and easily missed on x-ray. Always focus on site of common avulsion, with special attention to regions of soft tissue swelling
  • small avulsion fracture fragments are difficult to appreciate by MRI, and so avulsion injuries may be mislabeled as (intrasubstance) ligament rupture. Always re-review available x-rays when reading an MRI to detect subtle osseous defects and improve your awareness
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Case information

rID: 62452
Published: 18th Aug 2018
Last edited: 20th Aug 2018
Inclusion in quiz mode: Included
Institution: Mallinckrodt Institute of Radiology at Washington University

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