2025 ISAKOS Biennial Congress Paper
New MRI-based Radiologic Signs for the Assessment of Trochlea Dysplasia in Paediatric Population
Rafael Sales Fernández, MD, Salford UNITED KINGDOM
Tobi Oputa, FRCS, Machester, Bury UNITED KINGDOM
Vishesh Khanna, MRCS, MBBS, DNB ORTHOPAEDICS, New Delhi, DELHI UNITED KINGDOM
Wrightington, Wigan and Leigh NHS Foundation Trust, Wigan, Greater Mancherster, UNITED KINGDOM
FDA Status Cleared
Summary
This original paper describes new MRI based radiologic signs that can distinguish between normal and dysplastic trochleae in the paediatric population. The following new MRI based radiographic signs are described: the butterfly sign, the triangle sign, the highest point of the lateral trochlea and the ratio hTG/hLT. These radiologic signs allow for early diagnosis of trochlea dysplasia in children
Abstract
Background
Multiple variables have been described to define trochlea dysplasia in the adult population. These same variables are used to define trochlea dysplasia in children. Unlike adults, children have growth plates and trochlea dysplasia can develop or progress during the growing years.
Purpose
To describe the new MRI based radiologic signs of normal and abnormal trochleae in the paediatric population.
Method
312 knee MRI scans done in children aged 9 to 14 were retrospectively reviewed. Two cohorts of patients: patella instability (56) and no patella instability (256).
The following new MRI based radiographic qualitative and quantitative signs are described: the butterfly sign, the triangle sign, the highest point of the lateral trochlea and the ratio hTG/hLT.
The novel radiographic signs were compared to Dejour’s Classification in the patella instability group.
The Chi-Square Test was used to determine if the distribution of the radiologic signs was the same between two cohorts. Cramer’s V and rank-biserial correlation test was conducted to assess the strength of association between patella instability and the radiologic signs.
The sensitivity and specificity of the radiologic signs were calculated.
Results
312 patients (males 54%).
The differences observed in distribution of the radiologic signs between the two cohorts were statistically significant.
There was a statistically significant positive correlation between patella instability and the radiologic signs. This positive correlation was strong meaning that children with patella instability show abnormal radiologic signs. Cramer’s V showed a strong association between patella instability and the (abnormal) triangle sign (φc= 0.61), the highest point of the trochlea (φc= 0.69) and moderate association with the ratio hTG/hLT(φc=0.496).
The normal triangle was present in 77% of patients with no history of patella instability and can be considered a hallmark for normally developed trochlea. The reverse triangle had a specificity of 99% for patella instability and can be considered pathognomonic of moderate/severe dysplasia. The specificity of the ratio hTG/hLT is 99%.
None of the 24 patients diagnosed of trochlea dysplasia by Dejour’s classification had a normal triangle sign. 91.5% of patients with type D trochlea dysplasia showed a reverse triangle and 8.5% a transition triangle. Of the 29/56 patients in the patella instability who were considered to have a normal lateral x-ray by the Dejour classification, 7 had a normal triangle, 20 had a transition triangle and 2 a reverse triangle. We consider the discrepancy with Dejour’s the classification due to the triangle sign being a much more sensitive radiographic sign of changes in the development of the trochlea compared to plain x-rays.
Conclusion
These new MRI based radiologic signs can distinguish between normal and dysplastic trochleae in the paediatric population.
The normal triangle represents a normally developed trochlea. A reverse triangle represents moderate to severe trochlea dysplasia and is not compatible with normal function. The transition triangle represents either shallow trochlea or early abnormal development of trochlea dysplasia but is compatible with normal function.