Currently, instability of the meniscus has been a topic in the field of knee disorders. Particularly in instability of the lateral meniscus, the popliteomeniscal fascicles (PMFs) that are three small structures connecting the posterior horn of the lateral meniscus to the capsule of the knee joint may be thought to contribute to stability of the lateral meniscus. It is, however, quite difficult to detect the PMFs by conventional 2D MR imaging of the knee joint using 2D sequences because of their small size and complicated angulation. Recently, it has been reported that thin-slice 3D MR imaging using 3D FSE sequence with variable flip-angle refocusing RF pulses is very useful for detecting intraarticular abnormalities of the knee joint. Therefore, the purpose of this study was to assess the usefulness of thin-slice 3D MR imaging of the knee joint using 3D FSE sequence with variable flip-angle refocusing RF pulses for detecting the three PMFs of the lateral meniscus.29 knees in 29 patients (19 males and 10 females; mean age, 49years) with no symptom in the lateral compartment of the knee and no abnormality in the lateral meniscus on knee MR images were included. All MR images of the knee joint were obtained by a 3T MR scanner (Magnetom Skyra, Siemens Healthcare) and a 15-channel knee coil. Conventional 2D MR images including sagittal T2-weighted images, sagittal T1-weighted images, sagittal T2*-weighted images, and coronal fat-suppressed PD-weighted images with 3-4mm thicknesses were obtained. In addition, coronal fat-suppressed PD-weighted images with 0.6 mm thicknesses were obtained by using 3D FSE sequence with variable flip-angle refocusing RF pulses (SPACE) and multiplanar-reformatted (MPR) images of 1mm thickness were generated (thin-slice 3D MR images). The presence or absence of the three PMFs (posterosuperior, posteroinferior, and anteroinferior PMFs) were assessed by two radiologists. The percentages of the presence of the PMFs of the lateral meniscus were calculated on conventional 2D MR images and thin-slice 3D MR images. Regarding the anteroinferior PMF, MPR images were used to measure the angle of the posterior surface of the bilateral femoral condyles and anteroinferior PMF.Posterosuperior, posteroinferior, and anteroinferior PMFs were found in 16/29(55%), 12/29(41%), and 4/29(14%) on conventional 2D MR images and in 23/29(79%), 17/29(59%), and 28/29(97%) on thin-slice 3D MR images, respectively. In particular, the anteroinferior PMF was almost always found on thin-slice 3D MR images (P<0.05). The average angle of the posterior surface of the bilateral femoral condyles and anteroinferior PMF was 42 degree.Previous study using oblique sagittal 2D PD-weighted images (3mm) of knee MRI at 1.5T reported that anteroinferior and posterosuperior PMFs were found in 65-94% and 50-88%, respectively. Another study using 10 cadavaric knees obtained by 1.5T MRI reported that anteroinferior, posterosuperior, and posteroinferior PMFs were found in 100%, 40%, and 100%, respectively. In our study, the results from thin-slice 3D MR imaging are similar to those in the previous study using cadaveric knees. Interestingly, the anteroinferior PMF was almost always found by thin-slice 3D MR imaging.Thin-slice 3D MR imaging of the knee joint using 3D FSE sequence with variable flip-angle refocusing RF pulses may improve the visualization of the three PMFs of the lateral meniscus in comparison with conventional 2D MR imaging of the knee joint.