title: Investigations of Potential Phenotypes of Foot Osteoarthritis: Cross-Sectional Analysis From the Clinical Assessment Study of the Foot.
abstract: OBJECTIVE
  To investigate the existence of distinct foot osteoarthritis (OA) phenotypes based on pattern of joint involvement and comparative symptom and risk profiles.
  
  
  METHODS
  Participants ages ≥50 years reporting foot pain in the previous year were drawn from a population-based cohort. Radiographs were scored for OA in the first metatarsophalangeal (MTP) joint, first and second cuneometatarsal, navicular first cuneiform, and talonavicular joints according to a published atlas. Chi-square tests established clustering, and odds ratios (ORs) examined symmetry and pairwise associations of radiographic OA in the feet. Distinct underlying classes of foot OA were investigated by latent class analysis (LCA) and their association with symptoms and risk factors was assessed.
  
  
  RESULTS
  In 533 participants (mean age 64.9 years, 55.9% female) radiographic OA clustered across both feet (P < 0.001) and was highly symmetrical (adjusted OR 3.0, 95% confidence interval 2.1, 4.2). LCA identified 3 distinct classes of foot OA: no or minimal foot OA (64%), isolated first MTP joint OA (22%), and polyarticular foot OA (15%). After adjustment for age and sex, polyarticular foot OA was associated with nodal OA, increased body mass index, and more pain and functional limitation compared to the other classes.
  
  
  CONCLUSIONS
  Patterning of radiographic foot OA has provided insight into the existence of 2 forms of foot OA: isolated first MTP joint OA and polyarticular foot OA. The symptom and risk factor profiles in individuals with polyarticular foot OA indicate a possible distinctive phenotype of foot OA, but further research is needed to explore the characteristics of isolated first MTP joint and polyarticular foot OA.
authors.affiliation: Arthritis Research UK Primary Care Centre, Research Institute for Primary Care & Health Sciences, Keele University, Keele, Staffordshire, UK.
authors.forename: Trishna
authors.initials: T
authors.lastname: Rathod
authors.affiliation: Arthritis Research UK Primary Care Centre, Research Institute for Primary Care & Health Sciences, Keele University, Keele, Staffordshire, UK.
authors.forename: Michelle
authors.initials: M
authors.lastname: Marshall
authors.affiliation: Arthritis Research UK Primary Care Centre, Research Institute for Primary Care & Health Sciences, Keele University, Keele, Staffordshire, UK.
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Thomas
authors.affiliation: Arthritis Research UK Primary Care Centre, Research Institute for Primary Care & Health Sciences, Keele University, Keele, Staffordshire, UK, and Lower Extremity and Gait Studies Program, School of Allied Health, La Trobe University, Bundoora, Victoria, Australia.
authors.forename: Hylton B
authors.initials: HB
authors.lastname: Menz
authors.affiliation: Arthritis Research UK Primary Care Centre, Research Institute for Primary Care & Health Sciences, Keele University, Keele, Staffordshire, UK.
authors.forename: Helen L
authors.initials: HL
authors.lastname: Myers
authors.affiliation: Arthritis Research UK Primary Care Centre, Research Institute for Primary Care & Health Sciences, Keele University, Keele, Staffordshire, UK.
authors.forename: Elaine
authors.initials: E
authors.lastname: Thomas
authors.affiliation: Arthritis Research UK Primary Care Centre, Research Institute for Primary Care & Health Sciences, Keele University, Keele, Staffordshire, UK.
authors.forename: Thomas
authors.initials: T
authors.lastname: Downes
authors.affiliation: Arthritis Research UK Primary Care Centre, Research Institute for Primary Care & Health Sciences, Keele University, Keele, Staffordshire, UK.
authors.forename: George
authors.initials: G
authors.lastname: Peat
authors.affiliation: Arthritis Research UK Primary Care Centre, Research Institute for Primary Care & Health Sciences, Keele University, Keele, Staffordshire, UK.
authors.forename: Edward
authors.initials: E
authors.lastname: Roddy
mesh_terms: D000368:Aged; D003430:Cross-Sectional Studies; D005260:Female; D033023:Foot Joints / Q000000981:diagnostic imaging*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010003:Osteoarthritis / Q000000981:diagnostic imaging*; D010641:Phenotype; D011446:Prospective Studies; D011859:Radiography