Abstract
Introduction: Trochlear dysplasia is an important anatomical factor in symptomatic patellar instability. The impression at surgery is that the dysplasia is predominantly an abnormality of the proximal trochlea. There is a mismatch between the bony and cartilaginous trochlear anatomy in normal knees. This study assessed the mismatch in dysplastic trochleas.
Methods: The MRI scans of 25 knees in 23 patients with patellar instability and trochlear dysplasia were reviewed retrospectively. Axial fat saturation images where used to assess cartilaginous and bony trochlear morphology. The following parameters were measured in the three most proximal images of each trochlea:
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Cartilaginous and bony sulcus angles.
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Cartilage thickness in the sulcus and on both condyles.
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Morphology of the bony and cartilaginous surface contour (flat, convex or concave).
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Horizontal distance of the bony and cartilaginous sulcus measured from the lateral epicondyle.
Inter and intra observer error was recorded.
Results: There were 15 females and 8 males with an average age of 20.4 years (14 30).
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The average bony sulcus angle (SA) was 166.9 degrees (141 – 203) whereas the average cartilaginous SA was 184.8 degrees (152 – 222). In 74 of 75 axial images (98.6%) the cartilaginous SA was greater than the bony SA by an average of 17.6 degrees (3 45).
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The average cartilage thickness in the centre of the trochlea was 3.5 mm (1.4 – 5.2), and the thickness on the lateral and medial condyles were 2.2mm (1.8 3.5) and 1.9mm (0.6 3.3) respectively.
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In 74 of 75 axial images (98.6%) the cartilaginous contour was different to the osseous contour on subjective assessment. In 58 of 75 images (77.3%) the cartilaginous contour changed the bony morphology from concave to flat or convex, or from flat to convex. In 17 (22.6%) it reduced the concavity.
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The average horizontal distance of the bony sulcus from the lateral epicondyle was 33.7mm (24 42) and that of the cartilaginous sulcus 31.8mm (23 39).
Conclusion: This study demonstrates that the cartilaginous trochlear morphology differs markedly from that of the underlying bony trochlea in patients with trochlear dysplasia. Although the bony trochlea was dysplastic, the cartilage morphology worsened this abnormal shape. Since cartilage is poorly represented on routine radiography and computed tomography, MRI is necessary to demonstrate both the bony and cartilaginous morphology to facilitate surgical planning.
Theses abstracts were prepared by Professor Roger Lemaire. Correspondence should be addressed to EFORT Central Office, Freihofstrasse 22, CH-8700 Küsnacht, Switzerland.
