Pincer-type MRI morphology seen in over a third of asymptomatic healthy volunteers without femoroacetabular impingement

Background In daily routine, pincer femoroacetabular impingement (FAI) findings are often seen without a clinical diagnosis of pincer FAI. Purpose To assess the presence of pincer FAI MRI findings in asymptomatic volunteers with negative impingement test versus patients with clinically confirmed FAI. Study Type Case-control study. Population Sixty-three asymptomatic volunteers and 63 matched patients with FAI were included. Field Strength/ Sequence A coronal T-1-weighted turbo spin-echo sequence as well as a 3D oblique transverse water-excitation true fast imaging sequence at 1.5T. Assessment The volunteers underwent standard MRI of the hip, and patients underwent MR arthrography of the symptomatic hip using the same MR sequences. Measurements of cranial acetabular version, acetabular depth, and lateral center-edge angle were performed independently by three fellowship-trained musculoskeletal radiologists. Statistical Tests Descriptive statistics, Mann-Whitney U-test, Unpaired t-test, receiver operating characteristics (ROC), Intraclass correlation coefficient (ICC). Results Forty-one percent (26/63, reader 1), 32% and 37% (20 and 23/63, reader 2/3) of asymptomatic volunteers had at least one positive MR finding for pincer-FAI. Patients with pincer or mixed-type FAI had cranial retroversion of the acetabulum of -0.2 degrees +/- 7.1 (mean +/- standard deviation) for reader 1 and -0.3 degrees +/- 5.5/-0.2 degrees +/- 4.8 for reader 2 / reader 3, while asymptomatic volunteers had an anteversion of 6.2 degrees +/- 6.4 (reader 1) and 3.2 degrees +/- 4.9/3.1 degrees +/- 6.5 (readers 2/3): This difference was statistically significant (P <= 0.002), but there was a large overlap between the groups. Acetabular depth measurements were very similar for patients with either pincer or mixed-type FAI (5.1-5.3 mm +/- 3.1) and volunteers (5.2-6.1 mm +/- 2.6), without a statistically significant difference (P <= 0.50). Lateral center-edge angle was also similar in patients with either pincer or mixed-type FAI (32.1-35.1 degrees +/- 9.1) and volunteers (30.7-33.2 degrees +/- 6.5), without a statistically significant difference (P <= 0.28). Data Conclusion There is a large overlap in pincer-type MRI findings between patients with symptomatic FAI and asymptomatic volunteers. More than a third of volunteers exhibited at least one positive pincer-type MRI finding.