Occasionally, patients may have asymptomatic labral tears or developmental variations that mimic labral pathology. As a result, evaluation of the labrum to detect abnormalities before the onset of cartilage loss is among the most common indications for imaging of the hip. Tears occur most commonly in the anterior superior quadrant of the labrum. However, repetitive impingement and labral tears are a frequent cause of hip pain. Unlike the knee menisci, which have a load-bearing and cushioning function, and the glenoid labrum, which helps to deepen the glenoid fossa and improve glenohumeral contiguity, the acetabular labrum primarily seals the margins of the articular hyaline cartilage to prevent premature cartilage loss. The acetabular labrum is a fibrocartilaginous horseshoe-shaped structure along the anterior, superior, and posterior margins of the acetabular rim. This article describes the numerous variants of the hip that are frequently seen on arthrographic and nonarthrographic MR imaging examinations. As in any imaging study, it is important to be cognizant of these variations as well as associated findings that help distinguish between true abnormality and developmental variation when interpreting an MR image of the hip. Several developmental variations are seen in the hip, which can be mistaken for disease or potentially even contribute to the development of a pathologic condition.
MR imaging of the hip is one of the most common musculoskeletal MR imaging studies performed today to assess for occult fractures, acetabular labral tears, hyaline cartilage loss, and musculotendinous injuries.