Comparison of MRI and arthroscopy findings for transitional zone cartilage damage in the acetabulum of the hip joint

Objective To assess the performance of morphologic and hypointense signal changes on MRI to predict grades and types of acetabular cartilage damage in the chondrolabral transitional zone (TZ) of the hip identified at arthroscopy. Materials and methods This retrospective single-center study reviewed conventional 3T MRI hip studies from individuals with symptomatic femoroacetabular impingement (FAI) and subsequent hip arthroscopy surgery within 6 months. Independent review was made by three radiologists for the presence of morphologic damage or a hypointense signal lesion in the TZ on MRI. Fleiss’ kappa statistic was used to assess inter-reader agreement. The degree of TZ surfacing damage (modified Outerbridge grades 1–4) and presence of non-surfacing wave sign at arthroscopic surgery were collected. Relationship between sensitivity and lesion grade was examined. Results One hundred thirty-six MRI hip studies from 40 males and 74 females were included (mean age 28.5 years, age range 13–54 years). MRI morphologic lesions had a sensitivity of 64.9–71.6% and specificity of 48.4–67.7% for arthroscopic surfacing lesions, with greater sensitivity seen for higher grade lesions. Low sensitivity was seen for wave sign lesions (34.5–51.7%). MRI hypointense signal lesions had a sensitivity of 26.3–62% and specificity of 43.8–78.0% for any lesion. Inter-reader agreement was moderate for morphologic lesions ( k = 0.601) and poor for hypointense signal lesions ( k = 0.097). Conclusion Morphologic cartilage damage in the TZ on MRI had moderate sensitivity for any cartilage lesion, better sensitivity for higher grade lesions, and poor sensitivity for wave sign lesions. The diagnostic value of hypointense signal lesions was uncertain.