A considerable proportion of patients with adult spinal deformity (ASD) have concomitant hip osteoarthritis (HOA). However, no studies have systematically summarized the impacts of HOA on ASD patients, either radiologically or clinically.To compare the spinal sagittal alignment parameters pre- and postoperatively, along with patient-reported outcomes and complications following surgery in ASD patients with or without severe HOA (Kellgren-Lawrence grade 3-4).Systematic review and meta-analysis.We searched the PubMed, Embase, Scopus, Cochrane Library, Google scholar, ClinicalTrials.gov, ProQuest Dissertations and These, and Open Grey for articles with a publication cutoff of July 28, 2024. The inclusion criteria were: (1) comparative studies of ASD patients with and without severe HOA, (2) outcomes reported as spinal radiographic outcomes (such as pelvic tilt (PT), sacrofemoral angle (SFA), knee angle (KA), or sagittal vertical axis (SVA), etc.), patient-reported outcomes (such as SRS-22r, ODI, VR-12 PCS, etc.), and complications (such as proximal junctional kyphosis, pseudarthrosis, reoperation, etc.), and (3) randomized controlled trials and observational studies published in English. The exclusion criteria were (1) reviews, case series, case reports, letters, and conference reports, (2) in vitro biomechanical studies and computational modelling studies, (3) no report on study outcomes, and (4) studies with < 10 patients per group. Additionally, a two-sample mendelian randomization (MR) study using genetic variants associated with HOA as instrumental variables was conducted.Four observational studies with a total of 891 ASD patients (672 minimal HOA, 219 severe HOA) were included. Based on our meta-analysis, ASD patients with severe HOA exhibited significantly lower PT (95% CI: 0.09-0.57) and SFA (5% CI: 0.31-0.68), along with higher KA (95% CI: -0.52- -0.19), SVA (95% CI: -0.75- -0.41), global sagittal angle (95% CI: -0.71- -0.16), and posterior pelvic shift (95% CI: -0.93- -0.25) than those with minimal HOA. Furthermore, concomitant severe HOA was associated with higher postoperative SVA, worse VR-12 PCS, and increased risk of pseudarthrosis and reoperation based on a review of the literature. The MR study indicated a causal association between HOA and intervertebral disc degeneration related traits, including early lumbar prolapse (95% CI: 1.08-1.46), intervertebral disc disorders (95% CI: 1.07-1.32), and low back pain (95% CI: 1.02-1.17). Moreover, HOA was proven to relate to sarcopenia related traits, including usual walking pace (95% CI: -0.04- -0.02) and hand grip strength (95% CI: -0.06- -0.01).Radiologically, concomitant HOA in patients with ASD appears to be associated with limited pelvic compensatory capacity and worse global spinal sagittal alignment. Clinically, ASD patients with HOA may experience worse patient-reported outcomes and higher incidence of mechanical complications. Moreover, the presence of HOA promotes the progression of IVDD and sarcopenia, which could partially account for its impacts.Copyright © 2025. Published by Elsevier Inc.