Patient-Specific Medial Patellofemoral Ligament Femoral Footprint Mapping Using Compressed Lateral and Sagittal Sequence MRI in Patients With Trochlear Dysplasia

Background: Accurate identification of the medial patellofemoral ligament (MPFL) femoral footprint is essential for successful MPFL reconstruction. Standard tunnel placement techniques, such as the Schöttle method, rely on fixed sagittal radiographic landmarks and may not account for morphological patient variability, particularly in patients with trochlear dysplasia. The Compressed Lateral and Sagittal Sequence (CLASS) magnetic resonance imaging (MRI) method has been validated for assessing the native MPFL insertion and has been used to map its location in normal knees. However, it has not yet been applied to assess anatomical variability in dysplastic knees. The objective of this study was (1) to determine whether the MPFL femoral footprint differs between knees with and without trochlear dysplasia and (2) to assess whether the position of the MPFL footprint in trochlear dysplasia differs from the Schöttle point. Methods: MRI data from 58 dysplastic knees and 80 control knees were analyzed. The femoral MPFL footprint was identified using the CLASS method and projected onto a 2D coordinate system defined by the posterior femoral cortex ( y -axis) and a perpendicular line intersecting the most posterior point of Blumensaat’s line (x-axis). Statistical comparisons were made between groups and relative to the Schöttle reference point. A p-value of less than 0.05 was considered as statistically significant. Results: The femoral MPFL footprint in trochlear dysplasia was more anterior (2.05 ± 3.61 mm vs. 0.83 ± 3.39 mm; p = 0.044) and distal (–1.84 ± 4.09 mm vs. 1.44 ± 2.66 mm; p < 0.001) compared with knees without dysplasia. When referenced to the Schöttle point, a distal deviation was observed (mean difference: 4.84 ± 4.09 mm; p < 0.001), while there was no anteroposterior difference (0.75 ± 3.61 mm; p = 0.119). Conclusion: Trochlear dysplasia alters the femoral MPFL footprint, producing a significant systematic distal displacement compared with both normal knees and the Schöttle point, with a mean distal difference of 3.28 mm vs. normal knees and 4.84 mm relative to Schöttle point, emphasizing the anatomical variability overlooked by standardized landmarks. This supports the use of the CLASS algorithm for individualized tunnel placement in MPFL reconstruction. Level of Evidence: Level IV , diagnostic. See Instructions for Authors for a complete description of levels of evidence.