Conventional Radiographs and Magnetic Resonance Imaging for the Analysis of Trochlear Dysplasia: The Influence of Selected Levels on Magnetic Resonance Imaging.
BACKGROUND
Trochlear dysplasia is one of the most important risk factors for recurrent patellar instability. It is defined on true lateral conventional radiographs (CR) and axial magnetic resonance imaging (MRI). The type of trochlear dysplasia is decisive for surgical treatment; however, low agreement between CR and MRI has been reported.


OBJECTIVE
To compare the Dejour classification of trochlear dysplasia on CR and axial MRI using differing levels defined in the literature.


METHODS
Cohort study (diagnosis); Level of evidence, 2.


METHODS
The 4-type classification of trochlear dysplasia by Dejour was used to analyze 228 knees with recurrent patellar dislocations on true lateral CR and axial MRI. The 2-type modification of the Dejour classification was also similarly analyzed. Measurements on axial MRI were performed at 3 different levels: MR1, the most proximal level where the intercondylar notch forms a "Roman arch"; MR2, 3 cm above the joint line; and MR3, the midpatellar height.


RESULTS
MR1 was measured at a mean distance of 29 ± 3.5 mm and MR3 at a mean of 38 ± 5.8 mm above the joint line. MR1 and MR2 were always measured on the cartilaginous trochlea, whereas 52% of MR3 was found more proximally. Overall agreement was fair between CR and MR1/MR2 (31.1%/25.4%, respectively) and highest for MR3 (45.2%; P < .01). The highest agreement (81.8%) was found for MR3 with the 2-type trochlear dysplasia classification (low-grade trochlear dysplasia: type A vs high-grade trochlear dysplasia: types B, C, and D) and lower for MR1 (67.5%) and MR2 (62.0%).


CONCLUSIONS
Trochlear dysplasia measured on CR and MRI shows only fair agreement, especially when the supratrochlear region of the distal femur is not analyzed on axial MRI. MRI analysis that considers the cartilaginous trochlea only tends to underestimate the severity of dysplasia according to Dejour. For a more precise evaluation of trochlear dysplasia, the entire distal femur should be analyzed on axial MRI.
Department of Orthopaedics, Balgrist University Hospital, University of Zurich, Zurich, Switzerland.|Division of Orthopedics and Trauma Surgery, Geneva University Hospital, University of Geneva, Geneva, Switzerland.
Philippe Matthias
PM
Tscholl
Department of Orthopaedics, Balgrist University Hospital, University of Zurich, Zurich, Switzerland.
Florian
F
Wanivenhaus
Department of Orthopaedics, Balgrist University Hospital, University of Zurich, Zurich, Switzerland.
Sandro F
SF
Fucentese
D000293:Adolescent; D000328:Adult; D002648:Child; D015331:Cohort Studies; D005260:Female; D005269:Femur / Q000601:surgery; D006801:Humans; D007593:Joint Instability / Q000000981:diagnostic imaging* / Q000601:surgery; D007719:Knee Joint / Q000000981:diagnostic imaging* / Q000473:pathology; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D011859:Radiography / Q000379:methods*; D055815:Young Adult
Dejour; bias; classification; patellar instability; trochlear dysplasia