title: The relationship between clinical characteristics, radiographic osteoarthritis and 3D bone area: data from the osteoarthritis initiative.
abstract: BACKGROUND
  Radiographic measures of osteoarthritis (OA) are based upon two dimensional projection images. Active appearance modelling (AAM) of knee magnetic resonance imaging (MRI) enables accurate, 3D quantification of joint structures in large cohorts. This cross-sectional study explored the relationship between clinical characteristics, radiographic measures of OA and 3D bone area (tAB).
  
  
  METHODS
  Clinical data and baseline paired radiographic and MRI data, from the medial compartment of one knee of 2588 participants were obtained from the NIH Osteoarthritis Initiative (OAI). The medial femur (MF) and tibia (MT) tAB were calculated using AAM. 'OA-attributable' tAB (OA-tAB) was calculated using data from regression models of tAB of knees without OA. Associations between OA-tAB and radiographic measures of OA were investigated using linear regression.
  
  
  RESULTS
  In univariable analyses, height, weight, and age in female knees without OA explained 43.1%, 32.1% and 0.1% of the MF tAB variance individually and 54.4% when included simultaneously in a multivariable model. Joint space width (JSW), osteophytes and sclerosis explained just 5.3%, 14.9% and 10.1% of the variance of MF OA-tAB individually and 17.4% when combined. Kellgren Lawrence (KL) grade explained approximately 20% of MF OA-tAB individually. Similar results were seen for MT OA-tAB.
  
  
  CONCLUSIONS
  Height explained the majority of variance in tAB, confirming an allometric relationship between body and joint size. Radiographic measures of OA, derived from a single radiographic projection, accounted for only a small amount of variation in 3D knee OA-tAB. The additional structural information provided by 3D bone area may explain the lack of a substantive relationship with these radiographic OA measures.
authors.affiliation: Leeds Institute of Rheumatic and Musculoskeletal Medicine, University of Leeds and NIHR Leeds Musculoskeletal Biomedical Research Unit, Leeds, UK.
authors.forename: A J
authors.initials: AJ
authors.lastname: Barr
authors.affiliation: Leeds Institute of Rheumatic and Musculoskeletal Medicine, University of Leeds and NIHR Leeds Musculoskeletal Biomedical Research Unit, Leeds, UK.
authors.forename: B
authors.initials: B
authors.lastname: Dube
authors.affiliation: Leeds Institute of Rheumatic and Musculoskeletal Medicine, University of Leeds and NIHR Leeds Musculoskeletal Biomedical Research Unit, Leeds, UK.
authors.forename: E M A
authors.initials: EM
authors.lastname: Hensor
authors.affiliation: Leeds Institute of Rheumatic and Musculoskeletal Medicine, University of Leeds and NIHR Leeds Musculoskeletal Biomedical Research Unit, Leeds, UK.
authors.forename: S R
authors.initials: SR
authors.lastname: Kingsbury
authors.affiliation: Arthritis Research UK Primary Care Centre, Research Institute for Primary Care & Health Sciences, Keele University, UK.
authors.forename: G
authors.initials: G
authors.lastname: Peat
authors.affiliation: Imorphics Ltd, Kilburn House, Manchester, UK.
authors.forename: M A
authors.initials: MA
authors.lastname: Bowes
authors.affiliation: Leeds Institute of Rheumatic and Musculoskeletal Medicine, University of Leeds and NIHR Leeds Musculoskeletal Biomedical Research Unit, Leeds, UK. Electronic address: p.conaghan@leeds.ac.uk.
authors.forename: P G
authors.initials: PG
authors.lastname: Conaghan
mesh_terms: D000367:Age Factors; D000368:Aged; D001827:Body Height; D001835:Body Weight; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging / Q000473:pathology*; D006801:Humans; D021621:Imaging, Three-Dimensional; D016014:Linear Models; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D008962:Models, Theoretical; D009765:Obesity / Q000150:complications; D009929:Organ Size; D020370:Osteoarthritis, Knee / Q000150:complications / Q000000981:diagnostic imaging / Q000473:pathology*; D054850:Osteophyte / Q000000981:diagnostic imaging / Q000209:etiology / Q000473:pathology; D011859:Radiography; D013977:Tibia / Q000000981:diagnostic imaging / Q000473:pathology*
keywords: Knee; Magnetic resonance imaging; Osteoarthritis; Subchondral bone