CLASS-MRI validates patient-specific ACL footprints across variable fluoroscopic C-arm positioning: A cadaveric study

The aim of this study was (1) to investigate the accuracy of identifying the femoral and tibial anterior cruciate ligament (ACL) footprints (FPs) using the Compressed Lateral and Anteroposterior Anatomical Systematic Sequences (CLASS) method compared to the to the gold standard (anatomical dissection with direct FP marking, referred to as aCLASS); (2) to determine whether the planned CLASS corresponds to the fluoroscopic imaging used during surgery and (3) to determine whether the position of the C-arm matters.

Planned CLASS (pCLASS) accurately corresponds to anatomical CLASS (aCLASS) and to intraoperative fluoroscopy, with superior accuracy using contralateral C-arm positioning.

Ten cadaveric knees were used in this study. A magnetic resonance imaging (MRI) scan was obtained of the native and dissected knee. MRI images of the dissected knee with marked femoral and tibial ACL FPs were used to create the aCLASS. Additionally, the native MRI was used to identify the ACL FP to simulate preoperative planning and generate the pCLASS. True-lateral fluoroscopic images with the image receptor contralaterally and ipsilaterally positioned were obtained. Statistical tests included the Friedman test for positional comparison across all groups. One-way analysis of variance (ANOVA) with Bonferroni adjustment and paired two-way t test was conducted for clinically relevant groups, with p < 0.05 set as the level of statistical significance.

No significant differences were found among aCLASS, pCLASS, contralateral and ipsilateral measurements for femoral high-low (p = 0.753), femoral deep-shallow (p = 0.197) and tibial anterior-posterior (p = 0.106). ANOVA and paired t tests confirmed no significant difference between pCLASS and both fluoroscopic positions (all p > 0.05).

The CLASS method demonstrated no significant difference in FP localization compared with anatomic reference. This study validates CLASS as a reliable, patient-specific method for ACL FP identification that translates from preoperative MRI to intraoperative fluoroscopy regardless of whether the C-arm is positioned ipsilaterally or contralaterally. CLASS standardizes anatomical ACL reconstruction across diverse operative settings and surgeon experience levels.

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