Fig. 1.

a, b, c Different grades of rectus femoris strain depicted on MRI. a Axial Iw FS MRI shows only ill-defined hyperintensity around the myotendinous unit corresponding to mild edema (arrows), without significant associated fiber disruption (grade 1 strain). b Axial Iw FS MRI demonstrates a large well-defined hyperintensity corresponding to an area of intramuscular fiber disruption (arrows) filled by fluid/blood, affecting less than 50 % of the cross-sectional area of the muscle (grade 2 strain). Note the adjacent edema of the remaining fibers of the muscle as well as perifascial fluid. c Coronal Iw FS MRI shows a complete discontinuity of the proximal myotendinous unit (arrow), with a moderate amount of fluid/blood filling the gap (grade 3 strain)