In order to maintain sagittal alignment, subjects with adult spinal deformity (ASD), recruit compensation mechanisms such as pelvic retroversion and knee flexion, which are employed in standing position [1Barrey C., e al. Eur Spine J 2013 ;

Cliccare qui per andare alla sezione Riferimenti]. Hip morphology has been suggested as a factor in determining maximal pelvic retroversion. There are no studies on three-dimensional (3D) hip morphology, in standing position, in subjects with ASD. The aim was to determine whether 3D hip morphology and acetabular orientation are altered in ASD.

ASD and control subjects were recruited. Inclusion criteria for ASD patients were: age>18 years, the presence of back-related symptoms and at least one of the SRS-Schwab criteria [2Schwab F., e al. Spine 2012 ;

Cliccare qui per andare alla sezione Riferimenti]. All subjects underwent full body biplanar X-rays, in standing position, with 3D reconstruction of the spine, pelvis and lower limbs. Classic spino-pelvic alignment parameters were obtained as well as hip-specific ones bilaterally: acetabular anteversion, abduction and tilt (orientation of acetabulum in axial, frontal & sagittal planes), percentage of femoral head coverage by the acetabulum (%FHC), vertical center edge angle (VCE), anterior acetabular sector angle (AASA), posterior acetabular sector angle (PASA), neck shaft angle (NSA) and femoral anteversion. Spino-pelvic parameters were compared between ASD and control groups using Mann–Whitney's test. Hip parameters were compared between both groups bilaterally using mixed repeated measures ANOVA.

Sixty-six ASD (52F, age=45.4y [20–82]) and 130 control subjects (69F, age=29.3y [18–59]) were enrolled. ASD had altered spino-pelvic posture (P<0.05): increased SVA (15 vs. −13mm), C7-coronal plumb line (14 vs. 8mm), PI (55 vs. 50°), PT (20 vs. 11°), PI-LL (5 vs. −10°) and decreased TK (39 vs. 46°) and LL (50 vs. 61°). Subjects with ASD showed altered hip morphology (P<0.05): increased VCE (32 vs. 30°), %FHC (46 vs. 42%), acetabular tilt (31 vs. 23°), anteversion (22 vs. 17°), PASA (100 vs. 97°) and decreased AASA (58 vs. 60°) and NSA (127 vs. 129°).

This is the first study to investigate hip morphology and acetabular orientation in standing position in subjects with ASD. Subjects with ASD were found to have altered hip morphology characterized by increased posterior coverage (increased acetabular anteversion, tilt and PASA) and decreased anterior coverage (decreased AASA) as well as alterations in proximal femur morphology (decreased NSA) which can together lead to femoro-acetabular conflict. These alterations could contribute to the limitation of pelvic retroversion, which is an essential compensatory mechanism in sagittal malalignment.