MR imaging of the acetabular labrum: a comparative study of both hips in 180 asymptomatic volunteers.

The aim of this study was to determine the MR imaging characteristics of normal acetabular labra on both hips. Three hundred sixty acetabular labra on both hips of 180 asymptomatic volunteers were examined on a 0.5-T MR unit utilizing a superficial coil. T1-weighted and T2-weighted gradient-echo sequences (TR/TE/FA 169/10 ms/40 degrees, and 316/25 ms/40 degrees, respectively) were used. The volunteers were classified into five age groups (10-19, 20-29, 30-39, 40-49, and 50 + years of age). The shape (triangular, flat, round, absent), size, and the presence of intralabral foci of increased intensity (diffuse, linear, central, or basal) were noted on both labra in each volunteer, and symmetry-asymmetry of these features were investigated. The most common labrum shape was triangular, whereas absence of labrum was the least common condition. A difference of labral shapes between both hips was present in approximately 15% of volunteers. A size difference of over 25% between each labrum was noted in approximately one-fourth of volunteers. An age-related pattern of intralabral intensity increase was noted on both MR sequences (more commonly on T1-weighted gradient-echo images). Shape differences and age-related intensity changes of the acetabular labrum in the MR imaging of the hips were confirmed, and the possibility of variability of the labra, with regard to the shape and size, on both hips of the same individual was documented.