Objectives A standard lateral radiograph is the first step in the diagnostic workup in patients with posterior ankle pain. Because of overprojection by other structures at suboptimal radiographic projection angle, often an os trigonum is not discovered or erroneously be mistaken for a hypertrophic posterior talar process. The aim of this study was to identify the projection angles at which a radiograph is optimal for detecting bony impediments in patients suffering from posterior ankle impingement.
Methods Using ankle CT scans of patients with posterior ankle impingement, digitally reconstructed radiographs (DRRs) simulating 13 different radiographic projection angles were generated. The ankle CT scans served as a reference for the detection of an os trigonum and hypertrophic posterior talar process. Members of the Ankleplatform Study Group were invited to assess the DRRs, for presence or absence of an os trigonum or hypertrophic posterior talar process. Diagnostic accuracy and interobserver reliability were estimated for each projection angle. In addition, the diagnostic accuracy of the standard lateral view in combination with the rotated views was calculated.
Results High sensitivity for detecting an os trigonum was found for +15° (90.3%), +20° (81.7%) and +25° (89.7%) degrees of exorotation. Specificity in this range of projection angles was between 89.6% and 97.8%. Regarding the presence of a hypertrophic posterior talar process, increased sensitivity was found for +15° (65.7%), +20° (61.0%), +25° (60.7%), +30° (56.3%) and +35° (54.5%). Specificity ranged from 78.0% to 94.7%. The combination of the standard lateral view in combination with exorotated views showed higher sensitivity. For detecting an os trigonum, a negative predictive value of 94.6% (+15°), 94.1% (+20°) and 96.1% (+25°) was found.
Conclusion This study underlines the additional diagnostic value of exorotated views instead of, or in addition to the standard lateral view in detecting an osseous impediment. We recommend to use the 25° exorotated view in combination with the routine standard lateral ankle view in the workup of patients with posterior ankle pain.
Level of evidence Level III
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Contributors Conception or design of the work: RZ, JGGD, GJS and LB. Drafting the article: RZ and JJW. Custom software for generating DRR: JGGD. Data collection: RZ. Data analysis and interpretation: RZ.Critical revision of the article; final approval of the version to be published: all authors.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests None declared.
Ethics approval This study was performed in accordance with the current ethical standards (Declaration of Helsinki). Since the study was retrospective in design, based on already existing CT scans, approval by the local ethics committee was not required.
Provenance and peer review Not commissioned; externally peer reviewed.
Collaborators Ankle Platform Study Collaborative – Science of Variation Group:
Christian Plaaß; Leho Rips; Nacime Salomão Barbachan Mansur; Kandasam Sampathkumar; Muntean George Ovidiu; Alessandro Russo; Alon Burg; Harish Kurup; Andrzej Boszczyk; Rogier M. Gerards;Thomas Barwick; Jayaprasad P.S; David Kim; Ivan Bojanic; Nikica Darabos; Ettore Vulcano; Risi MicheleThomas Paulick; Mohan Kumar; Georges Laval; Theofanis Vasilakakos; Valeria Lopez Astegiano; Gaston Daguerre; Grzegorz Hajduk; Paolo Ceccarini; Víctor de Diego Gutiérrez; Christopher Brown; Örs Pécsi; Diederik Verbeek; Jai Thilak; Nikolaos Koukoulias; Samer El Hage; Vitor Miranda; Jeffrey Seybold; Angélica Millán; José de Arimathéa Brandão; Carolina Lins; Christopher Lu; Onur Bilge; Thijs M.J. Pahlplatz; Ivica Medenica; Horea Benea; Vaso Kecojevic; Enrique Leonardo Pasion; Ananya Puttaraju; Vish Kumar; Gonzalo Manuel; Perez Herrera; Luiz Amorim; Waleed Kishta; Xavier Madirolas; Raul Garcia Renedo; Pedro Diniz; Dimitrios Alexakis; Sharad Goyal; Nikos Gougoulias; Pedro Santos Leite; Kaya Husnu Akan; Simon CP Yuen; Rayan Baalbaki; Mario Marinelli; Alkiviadis Kalliakmanis; Nicholas Antao; Ahmed Ramy Soliman; Akvile Vilkyte; Rafael Tambascia; Bruno Pereira; Achim Preiss; Juan Mingo-Robinet; Ishanka Weerasekara; Brian Carpenter; Gustavo Adolfo Bacca Insuasty; Antonio Giadella; Christiaan J.A. van Bergen; Fransesco Lijoi; Hanneke Weel; Job N. Doornberg; Joris R. Lansdaal; Kim T.M. Opdam; Michael P. Bus; Miguel Viana Pereira Filho; Peter A.J. de Leeuw; Gabor Laszlo Szabo; Thomas S. Roukis; Vishal Upadhyay
Patient consent for publication Not required.
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