Validity of the Novel Radiological Classification System of the Distal Femur

Abstract

Objective Aseptic loosening (AL) is among the most important causes of failure after total knee arthroplasty (TKA). However, while there are numerous underlying causes of AL, the morphometry of the distal femur and intramedullary canal has not been sufficiently demonstrated. This study aimed to show the interobserver and intraobserver reliability and validity of the Citak classification, which has been recently defined according to the morphometry of the distal femur and provides a risk factor definition for AL.

Materials and Methods A total of 200 patients whose standardized anteroposterior (AP) and lateral images of the knee joint were obtained between October 2019 and April 2020 were retrospectively evaluated in this study. Patients with a history of extra-articular deformity and knee surgery were excluded from the study. For AL, morphologies of the distal femur were identified by two observers using the new radiological classification system of the distal femur. Mean pairwise Cronbach’s alpha coefficient was used to assess the intra- and interobserver agreement of the classification.

Results There was excellent interobserver agreement for the 20 cm proximal and 2 cm proximal to the lateral joint line (PLJL) and adductor tubercle (PAD), respectively. The mean Cronbach’s alpha coefficient was 0.96 (range 0.764–0.944) for the PAD and 0.98 (range 0.734–0.929) for the PLJL. There was also an excellent intraobserver agreement, with 93% average pairwise percent agreement for the index group and 95.5% average pairwise percent agreement for the anatomical classification group.

Conclusions The level of inter- and intraobserver agreement for the morphology of the distal femur was excellent in the new radiological classification system, which was shown to be beneficial in the planning of revision knee arthroplasty for AL. However, there is a need for further studies in order to make a correlation of the classification with specific intraoperative findings.

Zusammenfassung

Ziel Die aseptische Lockerung (AL) gehört zu den häufigen Ursachen nach Knie-Totalendoprothesen. Obwohl für die AL zahlreiche Ursachen zugrunde liegen, ist die Femuranatomie des distalen Femurs nicht ausreichend untersucht worden. Das Ziel dieser Studie war es, die Interobserver- und Intraobserver-Reliabilität und Validität der neuen Citak-Klassifikation zu untersuchen. Die Citak Klassifikation beschreibt 3 Formen des distalen Femurs, welche einen Risikofaktor für aseptische Lockerungen nach Implantation einer Rotationsknieprothese darstellen.

Material und Methoden Insgesamt wurden 200 Patienten, deren standardisierte anteroposteriore (AP) und laterale Aufnahmen des Kniegelenks zwischen Oktober 2019 und April 2020 angefertigt wurden, in dieser Studie retrospektiv ausgewertet. Patienten mit einer Vorgeschichte von extraartikulären Deformitäten und Knieoperationen wurden von der Studie ausgeschlossen. Für AL wurden die Morphologien des distalen Femurs von zwei Untersuchern unter Verwendung des neuen radiologischen Klassifikationssystems des distalen Femurs identifiziert. Der mittlere Cronbach-Alpha-Koeffizient wurde verwendet, um die Intra- und Interobserver-Übereinstimmung der Klassifikation zu beurteilen.

Ergebnisse Es gab eine exzellente Übereinstimmung für beide Untersucher. Der mittlere Cronbach-Alpha-Koeffizient betrug 0,96 (Bereich 0,764–0,944) für die Messungen am Adductor tubercle und 0,98 (Bereich 0,734–0,929) für die Messung 20 cm proximal der lateralen Gelenklinie. Auch gab es mit 93% eine ausgezeichnete Intraobserver-Übereinstimmung für den neuen radiologischen Index.

Schlussfolgerungen Es zeigt sich eine exzellenter Grad der Inter- und Intraobserver-Übereinstimmung für die Morphologie des distalen Femurs der neuen radiologischen Klassifikation. Es besteht jedoch weiterer Studienbedarf, um eine Korrelation der Klassifikation mit intraoperativen Befunden herzustellen.

Keywords

distal femur - radiological - classification - morphology

Schlüsselwörter

distales femur - Morphologie - Radiologisch - Klassifikation

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