Foot & Ankle International - July 2018 - 850

761035
research-article2018

FAIXXX10.1177/1071100718761035Foot & Ankle InternationalLawlor et al

Article

Weight-Bearing Cone-Beam CT Scan
Assessment of Stability of Supination
External Rotation Ankle Fractures in a
Cadaver Model

Foot & Ankle International®
2018, Vol. 39(7) 850-857
© The Author(s) 2018
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https://doi.org/10.1177/1071100718761035
DOI: 10.1177/1071100718761035
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Mark C. Lawlor, BS1, Melissa A. Kluczynski, MS1, and John M. Marzo, MD1

Abstract
Background: The utility of computed tomography (CT) for measuring medial clear space (MCS) for determination of the
stability of supination external rotation (SER) ankle fractures and in comparison to standard radiographs is unknown. We
compared MCS on gravity stress (GS) radiographs to GS and weight bearing (WB) cone-beam CT (CBCT).
Methods: An AO SER 44B3.1 ankle fracture was simulated in 10 human cadavers, also serving as controls. MCS was
measured on GS radiographs, GS CBCT, and a simulated WB CBCT scan. Specimens were stable if MCS was <5 mm and
unstable if MCS was ≥5 mm. Paired t tests were used to compare MCS from each imaging modality for controls versus SER
injuries and stable versus unstable specimens.
Results: Compared with controls assessed by GS radiographs, MCS was greater for an SER injury when assessed by GS
radiograph and GS CBCT scan within the stable group. Compared with controls assessed by GS radiographs, MCS was
greater for SER injuries when assessed by GS radiograph, GS CBCT scan, and WB CBCT within the unstable group. MCS
was reduced for stable versus unstable SER injuries assessed by WB CBCT.
Conclusion: In a cadaveric model of SER ankle fracture, the medial clear space was statistically significantly greater for the
experimental condition when assessed by gravity stress radiograph and gravity stress CBCT scan. Under weight-bearing
conditions, the cone-beam CT scanner distinguished between stable and unstable ankles in the experimental condition.
Clinical Relevance: This study suggests that a WB cone-beam CT scan may be able to distinguish between stable and
unstable SER ankle fractures and influence operative decision making.
Keywords: ankle fracture, CT scan, gravity stress, weight bearing

Introduction
When the lateral malleolus is fractured by excessive supination and external rotation (SER), the currently accepted
method for determining instability is to measure the medial
clear space distance on a stress radiograph, either manual or
gravity.9,20,26,31 While debated, the medial clear space should
be less than 4 mm, or no more than 1 mm greater than the
superior clear space.20,26 Previous studies, however, have
demonstrated that gravity stress radiographic measurements
may overestimate the number of patients in need of operative fixation.11,13,14,18,27,31 These authors report that weightbearing radiographs are more predictive of stability, and
patients with an anatomic mortise relationship can be successfully managed with immediate protected weight bearing and functional rehabilitation, without having to undergo
an operative procedure.
There has been a recent focus on computed tomography
(CT) of ankle fractures and syndesmotic disruption, but this

conventional CT technology has not yet become clinically
or economically practical.3,5,6,8,25 Recent studies on SER
injuries that involve the syndesmosis have shown that a
substantial amount of malrotation of the distal fibula can be
missed on standard radiographs, and when inadequately
treated, may lead to poor functional outcome.25 A new portable dedicated extremity cone-beam computed tomography (CBCT) scanner (OnSight, Carestream Health,
Rochester, NY) has been approved by the Food and Drug
Administration (FDA) for clinical use.2,12,28 This novel CT
scanner allows for imaging while fully weight bearing and
1

The Jacobs School of Medicine and Biomedical Sciences, The State
University of New York, University at Buffalo, Amherst, NY, USA
Corresponding Author:
Melissa A. Kluczynski, MS, UBMD Orthopaedics and Sports Medicine,
4949 Harlem Rd, Amherst, NY 14226, USA.
Email: mk67@buffalo.edu
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