Distances and angles in standing long-leg radiographs

Birkenmaier, Christof ; Levrard, Louise; Melcher, Carolin; Wegener, Bernd; Ricke, Jens; Holzapfel, Boris M.; Baur-Melnyk, Andrea und Mehrens, Dirk (2024): Distances and angles in standing long-leg radiographs. Comparing conventional radiography, digital radiography, and EOS. In: Skeletal Radiology, Bd. 53: S. 1517-1528

Abstract

Objective : Distances and angles measured from long-leg radiographs (LLR) are important for surgical decision-making. However, projectional radiography suffers from distortion, potentially generating differences between measurement and true anatomical dimension. These phenomena are not uniform between conventional radiography (CR) digital radiography (DR) and fan-beam technology (EOS). We aimed to identify differences between these modalities in an experimental setup.

Materials and methods : A hemiskeleton was stabilized using an external fixator in neutral, valgus and varus knee alignment. Ten images were acquired for each alignment and each modality: one CR setup, two different DR systems, and an EOS. A total of 1680 measurements were acquired and analyzed.

Results : We observed great differences for dimensions and angles between the 4 modalities. Femoral head diameter measurements varied in the range of > 5 mm depending on the modality, with EOS being the closest to the true anatomical dimension. With functional leg length, a difference of 8.7% was observed between CR and EOS and with the EOS system being precise in the vertical dimension on physical-technical grounds, this demonstrates significant projectional magnification with CR-LLR. The horizontal distance between the medial malleoli varied by 20 mm between CR and DR, equating to 21% of the mean.

Conclusions : Projectional distortion resulting in variations approaching 21% of the mean indicate, that our confidence on measurements from standing LLR may not be justified. It appears likely that among the tested equipment, EOS-generated images are closest to the true anatomical situation most of the time.

• Dokumententyp: Zeitschriftenartikel
• Fakultät: Medizin > Klinikum der LMU München > MUM - Muskuloskelettales Universitätszentrum München ; Medizin > Klinikum der LMU München > Klinik und Poliklinik für Radiologie
• Themengebiete: 600 Technik, Medizin, angewandte Wissenschaften > 610 Medizin und Gesundheit
• ISSN: 0364-2348
• Sprache: Englisch