Surgical outcomes, including radiographic outcomes, patient-reported outcomes, postoperative complications, and revision surgery rates, were compared in patients with adult spinal deformity who underwent correction surgery with reference to our pelvic incidence-dependent (PI-dependent) clustering of sagittal spinal alignment and existing standards (sagittal age-adjusted score [SAAS], global alignment and proportion [GAP] score, and Roussouly classification). Our findings may provide tangible guidance for surgical decision-making in ASD.

Inclusion Criteria:

1. ≥ 18 years of age at the time of treatment;
2. Complete radiographic data, including standing posteroanterior and lateral whole-spine radiographs, lumbar computed tomography, and lumbar magnetic resonance imaging;
3. Radiographic evidence of ASD: sagittal vertical axis ≥ 50 mm, pelvic tilt ≥ 25°, pelvic incidence-lumbar lordosis mismatch ≥ 10°, and/or thoracic kyphosis ≥ 60°.

Exclusion Criteria:

1. Any type of previous spinal surgery;
2. Other musculoskeletal problems impeding walking ability, syndromic or neuromuscular diseases such as Parkinson's disease, inflammatory conditions such as ankylosing spondylitis, infectious conditions such as spinal tuberculosis, metabolic diseases such as severe osteoporosis, and/or serious general medical conditions such as sepsis or malignancy;
3. Pathology of deformity as follows: post-traumatic deformity, adult idiopathic scoliosis of the thoracic spine, or de-novo lumbar scoliosis;
4. Hip joint Kellgren-Lawrence grade ≥ II, history of hip joint and/or knee joint pain, and/or previous joint replacement.