Accuracy and Precision of Anatomical Medial Patellofemoral Ligament Identification Using the CLASS MRI Method
Authors: Thürig Grégoire , Barrera Usó Marc , Panadero-Morales Raul , Alonso Domenech Elisabeth , Schwab Joseph M. , Tannast Moritz , Petek Daniel 
Published: February 2025

Background:
The medial patellofemoral ligament (MPFL) serves as the primary stabilizer of the patellofemoral joint, and surgical reconstruction aims to replicate its biomechanical properties. However, misplacement of the femoral tunnel remains a major problem that leads to revision after surgery for patellar instability. The C-arm technique for identifying the femoral origin of the MPFL (fMPFL) during surgery may not account for individual variability. Magnetic resonance imaging (MRI) allows for personalized fMPFL identification. The CLASS (Compressed Lateral and Anteroposterior Anatomical Systematic Sequences) method compresses MRI data into a lateral view, similar to intraoperative C-arm imaging. Recent research has shown that C-arm positioning directly affects fMPFL localization. The aim of this study was to investigate how accurate the identification of the femoral MPFL footprint is with the CLASS method and on which side the C-arm must be positioned.

Methods:
Ten Caucasian cadaveric knees were utilized in this study. MRIs of the native and dissected knee were obtained. The MRIs, with the fMPFL anatomy dissected and marked, were used to create the “anatomical CLASS” (aCLASS) data. Additionally, the “native MRI” was used to identify the fMPFL in order to simulate preoperative planning, generating the “planned CLASS” (pCLASS) data. True-lateral fluoroscopic images with the image receptor contralaterally or ipsilaterally positioned were obtained. Statistical tests included the Wilcoxon signed-rank test for positional comparisons across all groups. A 1-way analysis of variance (ANOVA) with the Bonferroni adjustment was conducted for clinically relevant groups. Significance was set at p < 0.05.

Results:
The pCLASS showed no significant differences compared with the aCLASS. The 1-way ANOVA showed significant differences between the ipsilateral group and the pCLASS and between the ipsilateral and contralateral groups only in the distal-proximal axis.

Conclusions:
This time-zero cadaveric study offers a novel method for determining the individual fMPFL. Various locations for femoral MFL attachment have been described in the literature, highlighting the need for individualized assessment methods. The CLASS method offered a reliable and reproducible approach for fMPFL identification. Also, proper intraoperative positioning of the C-arm, with the image receptor kept contralaterally, should be performed to increase the effectiveness of identifying the fMPFL using the CLASS method.

Clinical Relevance:
The CLASS method offers a personalized approach for accurately identifying the fMPFL during surgery, which could potentially reduce tunnel misplacement and revision rates. Proper C-arm positioning with contralateral image receptor placement enhances the effectiveness of this technique, which has the potential to improve outcomes for patients undergoing MPFL reconstruction for patellar instability.