title: A comparison of radiographic anatomic axis knee alignment measurements and cross-sectional associations with knee osteoarthritis.
abstract: OBJECTIVE
  Malalignment is associated with knee osteoarthritis (KOA), however, the optimal anatomic axis (AA) knee alignment measurement on a standard limb radiograph (SLR) is unknown. This study compares one-point (1P) and two-point (2P) AA methods using three knee joint centre locations and examines cross-sectional associations with symptomatic radiographic knee osteoarthritis (SRKOA), radiographic knee osteoarthritis (RKOA) and knee pain.
  
  
  METHODS
  AA alignment was measured six different ways using the KneeMorf software on 1058 SLRs from 584 women in the Chingford Study. Cross-sectional associations with principal outcome SRKOA combined with greatest reproducibility determined the optimal 1P and 2P AA method. Appropriate varus/neutral/valgus alignment categories were established using logistic regression with generalised estimating equation models fitted with restricted cubic spline function.
  
  
  RESULTS
  The tibial plateau centre displayed greatest reproducibility and associations with SRKOA. As mean 1P and 2P values differed by >2°, new alignment categories were generated for 1P: varus <178°, neutral 178-182°, valgus >182° and for 2P methods: varus <180°, neutral 180-185°, valgus >185°. Varus vs neutral alignment was associated with a near 2-fold increase in SRKOA and RKOA, and valgus vs neutral for RKOA using 2P method. Nonsignificant associations were seen for 1P method for SRKOA, RKOA and knee pain.
  
  
  CONCLUSIONS
  AA alignment was associated with SRKOA and the tibial plateau centre had the strongest association. Differences in AA alignment when 1P vs 2P methods were compared indicated bespoke alignment categories were necessary. Further replication and validation with mechanical axis alignment comparison is required.
authors.affiliation: MRC Lifecourse Epidemiology Unit, Faculty of Medicine, University of Southampton, Southampton, UK.
authors.forename: L M
authors.initials: LM
authors.lastname: Goulston
authors.affiliation: Oxford NIHR Musculoskeletal Biomedical Research Unit, Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Oxford, UK; Arthritis Research UK Sports Exercise and Osteoarthritis Centre of Excellence, University of Oxford, UK.
authors.forename: M T
authors.initials: MT
authors.lastname: Sanchez-Santos
authors.affiliation: MRC Lifecourse Epidemiology Unit, Faculty of Medicine, University of Southampton, Southampton, UK.
authors.forename: S
authors.initials: S
authors.lastname: D'Angelo
authors.affiliation: Oxford NIHR Musculoskeletal Biomedical Research Unit, Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Oxford, UK; Arthritis Research UK Sports Exercise and Osteoarthritis Centre of Excellence, University of Oxford, UK.
authors.forename: K M
authors.initials: KM
authors.lastname: Leyland
authors.affiliation: Department of Twin Research & Genetic Epidemiology, King's College London, London, UK.
authors.forename: D J
authors.initials: DJ
authors.lastname: Hart
authors.affiliation: Department of Twin Research & Genetic Epidemiology, King's College London, London, UK.
authors.forename: T D
authors.initials: TD
authors.lastname: Spector
authors.affiliation: MRC Lifecourse Epidemiology Unit, Faculty of Medicine, University of Southampton, Southampton, UK.
authors.forename: C
authors.initials: C
authors.lastname: Cooper
authors.affiliation: MRC Lifecourse Epidemiology Unit, Faculty of Medicine, University of Southampton, Southampton, UK.
authors.forename: E M
authors.initials: EM
authors.lastname: Dennison
authors.affiliation: Oxford NIHR Musculoskeletal Biomedical Research Unit, Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Oxford, UK; Chromatic Innovation Limited, Leamington Spa, UK.
authors.forename: D
authors.initials: D
authors.lastname: Hunter
authors.affiliation: MRC Lifecourse Epidemiology Unit, Faculty of Medicine, University of Southampton, Southampton, UK; Oxford NIHR Musculoskeletal Biomedical Research Unit, Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Oxford, UK; Arthritis Research UK Sports Exercise and Osteoarthritis Centre of Excellence, University of Oxford, UK. Electronic address: nigel.arden@ndorms.ox.ac.uk.
authors.forename: N K
authors.initials: NK
authors.lastname: Arden
mesh_terms: D000328:Adult; D000368:Aged; D059925:Anatomic Landmarks / Q000473:pathology; D017760:Bone Malalignment / Q000150:complications* / Q000000981:diagnostic imaging / Q000473:pathology; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000473:pathology*; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000000981:diagnostic imaging / Q000209:etiology* / Q000473:pathology; D010146:Pain / Q000209:etiology; D011446:Prospective Studies; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods; D011859:Radiography / Q000379:methods; D015203:Reproducibility of Results
keywords: Anatomic axis; Knee alignment; Knee osteoarthritis; Radiography