Abstract:Objective To investigate postoperative MRI findings after femoroacetabular impingement (FAI) arthroscopic surgery in correlation with pain changes.Methods We prospectively enrolled 42 patients (43 hips) who were scheduled for FAI arthroscopic surgery. Pre- and postoperative MRI were obtained using a 3.0T MRI system. Changes in pain were assessed using the hip disability and osteoarthritis outcome score (HOOS). Postoperative MRI were evaluated for the presence of acetabuloplasty or femoroplasty, presence of chondral and labral repair surgery, bone marrow edema, subchondral cysts, chondral defects, labral tears, capsular defects, and effusion.Results Increased acetabular bony débridement length was associated with decreased improvement in HOOS (OR^: -2.07, 95% CI: -3.53~-0.62, P = 0.008), whereas other imaging findings were not significantly different. Femoroplasty and capsular alterations were best detected on oblique axial sequences; acetabuloplasty and cartilage and labral repair were best seen on sagittal sequences. MRI showed excellent sensitivity (100.0%) and specificity (100.0%) for detecting labral repair and excellent sensitivity for detecting femoroplasty (97.7%). Sensitivity and specificity were lower for detecting acetabuloplasty (83.3% and 75.0%, respectively) and chondral repair (75.0% and 54.3%, respectively).Conclusion Arthroscopic acetabularplasty is associated with postoperative pain.