Postoperative Effusion-Synovitis is Associated With Poor Clinical Outcomes in Patients With Femoroacetabular Impingement Syndrome: a Consecutive Magnetic Resonance Imaging Study.

Purpose: (1) to investigate the consecutive changes in effusion-synovitis following primary arthroscopic treatment for patients with femoroacetabular impingement syndrome (FAIS), and (2) to determine the effect of postoperative effusion-synovitis on clinical outcomes.

Methods: Data between March 2021 and January 2022 was reviewed. Patients diagnosed with FAIS and undergoing hip arthroscopic treatment were included. Exclusion criteria were incomplete magnetic resonance imaging (MRI) data, prior history of hip surgery, labral reconstruction, and concomitant hip conditions. MRI (non-contrast 3.0 T) was performed preoperatively and 3, 6, 12-month postoperatively, and the measurement of the largest femoral neck fluid thickness (FTM) and cross-sectional area (CSA) of the effusion-synovitis were collected. Preoperative and a minimum of 2-year postoperative patient-reported outcome (PRO) scores including Visual Analog pain Scale (VAS), modified Harris Hip Score (mHHS), and international Hip Outcome Tool, 12-component form (iHOT-12) were collected and compared. Postoperative Tegner activity scale was also collected. The PROs and achievements of minimal clinically important difference (MCID) and patient acceptable symptom state (PASS) were compared between patients with and without postoperative effusion-synovitis. Multivariate linear regression analysis was performed to determine the effect of the effusion-synovitis size on PROs.

Results: A total of 61 patients (61 hips) were included in the study. The 3-month postoperative FTM, CSA and grade of effusion-synovitis presented a significant increase compared to the preoperative values (all with P < .05). No significant differences were observed in the 6-month postoperative measurements compared to the preoperative values (all with P > .05). At the 12-month follow-up, although there was a significant decrease in all measurements compared to the preoperative values (all with P < .001), 39 patients (63.9%) still presented effusion-synovitis. Compared to the other 22 patients (36.1%) without effusion-synovitis, these patients presented inferior mHHS, iHOT-12 (all with P < .05), as well as lower achievement of PASS of mHHS (82.1% vs 100%, P = .035) and iHOT-12 (38.5% vs 81.8%, P = .001). The achievement of MCID of mHHS (79.5% vs 77.3%, P = .839) and iHOT-12 (89.7% vs 95.5%, P = .839) were comparable between patients with and without effusion-synovitis. The postoperative sagittal CSA (Beta = -.302, P = .039) were negatively related to mHHS in the regression analysis.

Conclusion: After arthroscopic treatment for FAIS, the level of effusion-synovitis presented an initial increase, then followed by a subsequent decrease. Effusion-synovitis was significantly alleviated at 12 months compared to the preoperative level. Patients with postoperative effusion-synovitis had inferior clinical outcomes and lower achievement of PASS compared to those without.

Level of evidence: Level IV; retrospective case series.