Location and Correlation of Acetabular Labral Tears and Paralabral Cysts Using Magnetic Resonance Imaging or Magnetic Resonance Arthrography in Patients With Femoroacetabular Impingement.

PURPOSE: To evaluate the prevalence and location of paralabral cysts and the correlation between the type of femoroacetabular impingement (FAI) and acetabular labral tears, as well as the location of the paralabral cysts. METHODS: Patients who received a diagnosis of FAI syndrome using plain radiography, magnetic resonance imaging or magnetic resonance arthrography, or computed tomographic arthrography from 2010 to 2015 were included in this study. The exclusion criteria were patients with arthritis (Tönnis grade 2 or greater) or dysplasia. We identified paralabral cysts and their location, size, configuration. Correlations between the type of FAI and labral tears and paralabral cysts were analyzed using the χ-square test. RESULTS: Among 506 patients with FAI, paralabral cysts were found in 51 patients (55 hips) and were located anterosuperiorly in 40% of cases, posterosuperiorly in 36%, anteroinferiorly in 17%, and posteroinferiorly in 8%. We identified multilocular cysts in 60% of hips and unilocular cysts in 40%. Labral tears were radiographically found in 44 of 55 hips with paralabral cysts (80%); they were located anterosuperiorly in 59% and posterosuperiorly in 41%. Although paralabral cysts were found in the anteroinferior and posteroinferior areas, acetabular labral tears were not identified in the anteroinferior and posteroinferior areas. Classification of the type of FAI showed cam type in 14 of 55 hips (25.5%), pincer type in 16 (29%), mixed type in 7 (13%), labral tears in 15 (27%), and normal findings in 3 (5.5%). No correlation was found between the type of FAI and labral tears (P = .739) or the location of paralabral cysts (P = .228). CONCLUSIONS: Paralabral cysts in patients with FAI most commonly are found in the anterosuperior area and are of the multilocular type. Although paralabral cysts in the anterosuperior and posterosuperior portions are related to labral tears, those in the anteroinferior and posteroinferior portions are not. LEVEL OF EVIDENCE: Level IV, diagnostic case series.