Morphological Classification of Trochlear Dysplasia Based On Three-Dimensional Models

Background: Trochlear dysplasia (TD) is a common risk factor for the development of patellofemoral instability (PI). Dejour’s classification shows low agreement between conventional radiography and axial magnetic resonance imaging. The present study aimed to evaluate and categorize the true lateral view of three-dimensional (3D) femoral models in patients with TD. Methods: Computed tomography (CT) scans of 96 hip-knee-ankle joints (49 PI patients: 34 female, 15 male; mean age 19.1±6.7 years, range 12–41 years) during 2017–2019 were collected and analyzed. A senior orthopedic surgeon classified the true lateral views of femoral 3D models and raw CT images. The crossing-point site and lateral condyle/facet morphology (lateral condyle bump or supratrochlear spur) were the main criteria. Results: TD cases were classified into four types and their frequencies recorded: type 1 (7.3%) = crossing-point site in the proximal trochlear area and no lateral condyle bump or supratrochlear spur; type 2 (19.8%) = crossing-point site in the proximal trochlear area and presence of a lateral condyle bump or supratrochlear spur; type 3 (13.5%) = crossing-point site in the distal trochlear area and no lateral condyle bump or supratrochlear spur; type 4 (59.4%) = crossing-point site in the distal trochlear area and presence of lateral condyle bump or supratrochlear spur.Conclusion: The presentation of TD varies greatly among PI patients and can be categorized into four types. This new classification, based on true lateral views of 3D femoral models, may provide relatively reliable guidance when using trochleoplasty to treat TD. Level of Evidence: II, development of diagnostic or monitoring criteria in consecutive patients.