Reliability of pre-operative symptoms, radiographs, and MRI for the assessment of cartilage loss in patients with femoroacetabular impingement syndrome with intra-operative correlation.

Objective: To assess the correlation of pre-operative symptoms, pre-operative diagnostic imaging for cartilage loss, and intra-operative cartilage findings in patients undergoing hip arthroscopy for femoroacetabular impingement syndrome.

Materials and methods: Three radiologists performed retrospective independent reviews of pre-operative MRIs in 96 hips for acetabular/femoral cartilage loss utilizing a simplified "high-low" classification and the International Cartilage Repair Society grading system. Severity of supra-foveal central femoral head cartilage loss was separately noted. Pre-operative radiographs were graded using the Tonnis and Kellgren-Lawrence systems and for central joint space narrowing. Pre-operative patient symptoms were prospectively gathered utilizing the Nonarthritic Hip Score and the modified Harris Hip Score. Intra-operatively, cartilage loss was recorded using the Outerbridge system.

Results: A moderate-to-strong positive correlation between pre-operative radiographic and MR cartilage loss was observed (0.21 $\le$ Τ $\le$ 0.53, T = Kendall's tau) for all readers/scales. Weak-to-moderate positive correlation was found between intra-operative cartilage grading and radiographic grading (0.10 $\le$ Τ $\le$ 0.30). Weak-to-moderate positive correlation between MRI and intra-operative cartilage grading was found for all readers/grading systems (0.17 $\le$ Τ $\le$ 0.43). Cartilage defects were slightly under-reported on MRI, reaching statistical significance at the femoral head. There was moderate-to-strong positive correlation between radiographic central joint narrowing and MRI central femoral head cartilage loss (0.35 $\le$ Τ $\le$ 0.55) for all readers. Inter-reader reliability was fair-to-moderate for radiographs, but poor for MRI. Clinical scores demonstrated very weak negative to no correlation with radiographic/MR cartilage findings and weak positive correlation with intra-operative cartilage findings.

Conclusion: Despite MRI underestimation of cartilage loss, the very weak-to-weak correlation of clinical symptoms with pre-operative imaging and intra-operative findings emphasizes the importance of MRI in pre-operative evaluation.