Radiographic Categorization of the Hip-spine Syndrome in the Setting of Hip Osteoarthritis and Sagittal Spinal Malalignment

Abstract

Interplay between degenerative hip and spine conditions (Hip-Spine Syndrome [HiSS]) warrants effective communication between respective surgeons. We identified radiographic parameters to distinguish a subset of patients with HiSS by evaluating hip osteoarthritis (HOA) in patients with and without spinopelvic malalignment, categorizing patients into respective HiSS types, and comparing radiographic parameters. All patients with full-body orthogonal radiography from 2013 to 2016 were reviewed (n = 1,389). Using sagittal/coronal hip radiographs, HOA (Kellgren-Lawrence Grade) was noted, and pelvic incidence-lumbar lordosis mismatch (PI-LL) > 10° was considered spinal malalignment. Patients groups included non-HiSS (PI-LL ≤ 10°/Grade 0/n = 444), Hip (PI-LL ≤ 10°/Grade 3-4/n = 78), Spine (PI-LL > 10°/Grade 0/n = 297), or Hip-Spine (PI-LL > 10°/Grade 3-4/n = 30). Parameters were compared using ANOVA with post-hoc Bonferroni analysis. HiSS Hip type patients had less hip extension capability compared with non-HiSS, Spine, and Hip-Spine type patients, reflected by lowest pelvic tilt (PT)/sagittal retroversion (11.3° versus 16.5°/29.2°/25.2°, respectively) and less hip extension per sacrofemoral angle (10.1° versus 19.5°/28.4°/23.1°, respectively) (P < 0.001), as well as 4.7° increase in anterior tilt/sagittal anteversion compared with age-matched individuals. Hip-Spine type patients had less pelvic retroversion than Spine type patients (P = 0.045); these differences were greater when referenced to age-matched individuals (P < 0.001). Hip-Spine type patients had less hip extension than Spine type patients (P = 0.013). Hip type patients had greater knee flexion than non-HiSS type patients (6.4° versus 2.6°; P < 0.001). Moreover, Hip-Spine type patients had comparable lower extremity alignment compared with Spine type patients, except for greater posterior pelvic shift. Our novel HiSS categorization used established classification methods and supported PT use to potentially improve the ability to discern HiSS types/pathologies in a subset of patients with HOA and spinal sagittal malalignment. HOA grade 3 to 4 with PT <15° are categorized as Hip type and those with PT >25° are Hip-Spine type with sagittal malalignment, which may impact acetabular arthroplasty component placement.