Imaging appearance and distribution of intra-articular adhesions following open FAI surgery.

Objectives: To evaluate the appearance and distribution of intra-articular adhesions on direct MR arthrograms (MRA) in symptomatic patients after surgical hip dislocation (SHD) for the treatment of femoroacetabular impingement (FAI).

Methods: All 18 patients (19 hips) who underwent arthroscopic debridement for treatment of symptomatic adhesions after open surgery of FAI between 2003 and 2012 and that had a complete set of pre- and postoperative direct MRA were evaluated. On radial PD-w images, pre- and postoperative osseous alpha angles were measured. Signal intensity and degree of obliteration of the peripheral compartment of the hip joint were assessed circumferentially at each 'half-hour' position and quantified with the adhesion alpha angle (measured between a line connecting the most proximal appearance of adhesions on the femoral neck with the femoral head center and the femoral neck axis). Linear regression analysis was performed between the site of correction and adhesions. As a control group, all patients (9; 9 hips) that underwent revision surgery during the same time period in which adhesions were not the primary cause for revision were evaluated.

Results: Femoral adhesions primarily (47%) appeared as intermediate, complete obliterations correlating with the site of offset correction (R = 0.883, p < 0.001). Adhesion alpha angles were comparable to the pre-operative osseous alpha angles (21/24 positions, p > 0.05) and were greater than the postoperative osseous alpha angles (11/24 positions, p < 0.05). Most labral adhesions (83.2%) appeared as adjacent and correlated with the site of rim trimming (R = 0.777, p < 0.001). In the control group, the most common reason for revision surgery was persisting cam deformity (67%). The radiographic findings were confirmed intra-operatively.

Conclusion: Intra-articular adhesions most commonly appear at the site of primary offset correction. Recurrent impingement due to scar tissue may be quantified with the adhesion alpha angle. MRA of the hip are suitable to distinguish between postoperative adhesions and other known causes for persisting symptoms.