Assessment of Cam-Type Femoroacetabular Impingement by Ultrasonography: Value of Anterior Femoral Distance Measurements

Abstract

Purpose: To retrospectively determine the reproducibility and performance of a quantitative measurement for cam-type femoroacetabular impingement (FAI) designated as the anterior femoral distance (AFD) of the femoral head-neck junction identified at ultrasonography (US).

Materials and Methods: 72 patients with clinically suspected FAI were retrospectively evaluated, and US studies were performed during a 20-month period. Of these, we selected 53 patients who underwent subsequent magnetic resonance (MR) arthrography and had adequate recorded US images. All the longitudinal US images of the anterior and anterosuperior contours of the femoral head-neck junction were recorded by a radiologist. 33 of these US images were also recorded by a technician. An alpha angle of > 55° on MR arthrography was indicative of cam-type FAI. Two independent radiology residents blinded to the clinical data and MR arthrography measured the maximal femoral head-neck overgrowth defined as the AFD on US (AFD-US). Reproducibility was assessed using intra-class correlation coefficients (ICCs) and Bland-Altman plots, and diagnostic performance was assessed using receiver operating characteristic (ROC) analysis.

Results: AFD-US showed high intra- and inter-rater agreement (ICC = 0.913 – 0.968) in all measurements and good reproducibility among different operators in the anterior contour measurements (ICC = 0.881) but not in the anterosuperior contour measurements (ICC = 0.196). An AFD-US cut-off value of 4.0 mm in the anterior contour yielded the greatest sensitivity (80.9 %) and specificity (87.5 %) for the diagnosis of cam-type FAI by ROC analysis.

Conclusion: AFD-US of the anterior contour of the femoral head-neck junction is helpful in diagnosing cam-type FAI.

Zusammenfassung

Ziel: Die retrospektive Bestimmung der Reproduzierbarkeit und Leistung der quantitativen Messung beim „cam-type“ femoroacetabulären Impingement (FAI), die als anterior-femorale Distanz (AFD) des Femurkopf-/Schenkelhals-Übergangs im Ultraschall (US) bestimmt wird.

Material und Methoden: Retrospektiv wurden 72 Patienten mit klinischem Verdacht auf FAI bewertet und US-Untersuchungen über einen Zeitraum von 20 Monaten durchgeführt. Davon wählten wir 53 Patienten aus, die sich in Folge einer Magnetresonanz(MR)- Arthrografie unterzogen und die ausreichend dokumentierte US-Bilder besaßen. Alle longitudinalen US-Bilder der anterioren oder anterosuperioren Konturen des Femurkopf-/Schenkelhals-Übergangs wurden durch einen Radiologen aufgenommen; 33 dieser US-Bilder wurden auch durch einen Techniker aufgenommen. Ein Alphawinkel von > 55° in der MR-Arthrografie sprach für ein „cam-type“ FAI. Zwei unabhängige niedergelassene Radiologen bestimmten verblindet zu den klinischen Daten und der MR-Arthrografie die maximale Überwucherung des Femurkopf-/Schenkelhalses, der als AFD im US (AFD-US) definiert wurde. Die Reproduzierbarkeit wurde durch Intraklassen-Korrelationskoeffizienten (ICCs) und durch Bland-Altman-Diagramme bewertet; die diagnostische Leistung wurde mittels Receiver-Operating-Characteristic(ROC)-Analyse ermittelt.

Ergebnisse: AFD-US zeigte bei allen Messungen eine hohe Intra- und Interrater-Übereinstimmung (ICC = 0,913 – 0,968) und eine gute Reproduzierbarkeit zwischen den verschiedenen Anwendern für die anteriore Kontur (ICC = 0,881), jedoch nicht für die anterosuperioren Konturmessungen (ICC = 0,196). Ein AFD-US Grenzwert von 4,0 mm der anterioren Kontur erzielte nach der ROC-Analyse die höchste Sensitivität (80,9 %) und Spezifität (87,5 %) für die Diagnose eines „cam-type“ FAI.

Schlussfolgerung: AFD-US der anterioren Kontur des Femurkopf-/Schenkelhals-Übergangs unterstützt die Diagnose des „cam-type“ FAI.

Key words

hip - cam deformity - femoroacetabular impingement - ultrasonography - magnetic resonance image

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