Alterations of 3D acetabular and lower limb parameters in adolescent idiopathic scoliosis.

PURPOSE: To evaluate the 3D deformity of the acetabula and lower limbs in subjects with adolescent idiopathic scoliosis (AIS) and their relationship with spino-pelvic alignment. METHODS: Two hundred and seventy-four subjects with AIS (frontal Cobb: 33.5 degrees +/- 18 degrees [10 degrees -110 degrees ]) and 84 controls were enrolled. All subjects underwent full-body biplanar X-rays with subsequent 3D reconstructions. Classic spino-pelvic and lower limb parameters were collected as well as acetabular parameters: acetabular orientation in the 3 planes (tilt, anteversion and abduction), center-edge angle (CEA) and anterior and posterior sector angles. Subjects with AIS were represented by both lower limb sides and classified by elevated (ES) or lowered (LS), depending on the frontal pelvic obliquity. Parameters were then compared between groups. Determinants of acetabular and lower limb alterations were investigated among spino-pelvic parameters. RESULTS: Acetabular abduction was higher on the ES in AIS (59.2 degrees +/- 6 degrees ) when compared to both LS (55.6 degrees +/- 6 degrees ) and controls (57.5 degrees +/- 3.9 degrees , p < 0.001). CEA and acetabular anteversion were higher on the LS in AIS (32 degrees +/- 6.1 degrees , 20.5 degrees +/- 5.7 degrees ) when compared to both ES (28.7 degrees +/- 5.1 degrees , 19.8 degrees +/- 5.1 degrees ) and controls (29.8 degrees +/- 4.8 degrees , 19.1 degrees +/- 4 degrees , respectively, p < 0.001). Anterior sector angle was lower on both ES and LS in AIS when compared to controls. CEA, acetabular abduction and acetabular anteversion were found to be mostly determined (adjusted R(2): 0.08-0.32) by pelvic tilt and less by frontal pelvic obliquity, frontal Cobb and T1T12. CONCLUSIONS: Subjects with AIS had a more abducted acetabulum at the lowered side, more anteverted acetabulum and a lack of anterior coverage of both acetabula. These alterations were strongly related to pelvic tilt.