Normal anatomic variants of the acetabular labrum

Within the past two decades, magnetic resonance imaging (MRI) has evolved into an integral part of noninvasive diagnostic testing for evaluation of musculoskeletal disorders. With the advancements in imaging and coil technology, assessment of small and spatially complex structures, such as the acetabular labrum, became possible. Labral tears are being diagnosed with increasing frequency with MRI. However, the medical literature reveals erratic sensitivity and specificity values of MRI, including MR arthrography, in identifying labral tears. This finding could be partly attributable to false-positive results caused by normal anatomic variants of the acetabular labrum. Additional challenges are introduced by the lack of consensus on the existence and the distributions of the normal anatomic variants of the labrum in MRI and orthopedic literature. In this article, the spectrum and incidence of these variations are discussed with emphasis on MRI features of the variant anatomy and the labral tears.