Usefulness of the fast spin-echo multi-point Dixon image of the knee joint on 3.0 T MRI for evaluation of meniscal tear

Background: It remains unclear whether a torn meniscus loses significantly more fat content than a normal meniscus and consequently shows a lower signal drop on opposed-phase (OP) images using the multi-point Dixon (mDixon) technique. Purpose: To evaluate meniscal injuries by performing a quantitative analysis of internal fat content using a signal drop. Material and Methods: A total of 99 patients who underwent knee magnetic resonance imaging (MRI) with the mDixon technique was included in this retrospective study. We measured the mean signal intensity of the meniscus from the in-phase (IP) and OP mDixon images with sagittal reconstruction. The proportional decrease of signal intensity (signal drop) was calculated. The median value with 25th (Q1) and 75th (Q3) percentiles of signal drop was reported for each meniscus. The Mann–Whitney U-test was used to compare the signal drop between meniscal tear and normal groups. Results: In the lateral meniscus (LM) and medial meniscus posterior horn (MMPH) tear groups, the median values of signal drop were significantly lower than in the normal group (P <0.05). Although the MM anterior horn (MMAH) tear group had a lower median signal drop than the normal group, there was no significant difference (P = 0.116 and 0.283, readers 1 and 2, respectively). Conclusion: The signal drop in torn menisci was lower than in normal menisci across all tear types, with statistical significance observed in LM and MMPH tears. We believe that these results may be explained by a reduced intracellular lipid content in torn menisci compared to normal menisci.