title: Genetic factors contribute more to hip than knee surgery due to osteoarthritis - a population-based twin registry study of joint arthroplasty.
abstract: To explore and quantify the relative strengths of the genetic contribution vs the contribution of modifiable environmental factors to severe osteoarthritis (OA) having progressed to total joint arthroplasty.
  
  
  
  Incident data from the Norwegian Arthroplasty Registry were linked with the Norwegian Twin Registry on the National ID-number in 2014 in a population-based prospective cohort study of same-sex twins born 1915-60 (53.4% females). Education level and height/weight were self-reported and Body Mass Index (BMI) calculated. The total follow-up time was 27 years for hip arthroplasty (1987-2014, 424,914 person-years) and 20 years for knee arthroplasty (1994-2014, 306,207 person-years). We estimated concordances and the genetic contribution to arthroplasty due to OA in separate analyses for the hip and knee joint.
  
  
  
  The population comprised N = 9058 twin pairs (N = 3803 monozygotic (MZ), N = 5226 dizygotic (DZ)). In total, 73% (95% confidence intervals (CI) = 66-78%) and 45% (95% CI = 30-58%) of the respective variation in hip and knee arthroplasty could be explained by genetic factors. Zygosity (as a proxy for genetic factors) was associated with hip arthroplasty concordance over time when adjusted for sex, age, education and BMI (HR = 2.98, 95% CI = 1.90-4.67 for MZ compared to DZ twins). Knee arthroplasty was to a greater extent dependent on BMI when adjusted for zygosity and the other covariates (HR = 1.15, 95% CI = 1.02-1.29).
  
  
  
  Hip arthroplasty was strongly influenced by genetic factors whereas knee arthroplasty to a greater extent depended on a high BMI. The study may imply there is a greater potential for preventing progression of knee OA to arthroplasty in comparison with hip OA.
authors.affiliation: National Advisory Unit on Rehabilitation in Rheumatology, Department of Rheumatology, Diakonhjemmet Hospital, Oslo, Norway. Electronic address: magnusson_karin@hotmail.com.
authors.forename: K
authors.initials: K
authors.lastname: Magnusson
authors.affiliation: Australian Centre of Excellence in Twin Research, Centre for Epidemiology & Biostatistics, University of Melbourne, Melbourne, Australia.
authors.forename: K
authors.initials: K
authors.lastname: Scurrah
authors.affiliation: Norwegian Institute of Public Health, Oslo, Norway; Department of Psychology and the School of Pharmacy, University of Oslo, Oslo, Norway.
authors.forename: E
authors.initials: E
authors.lastname: Ystrom
authors.affiliation: Norwegian Institute of Public Health, Oslo, Norway.
authors.forename: R E
authors.initials: RE
authors.lastname: Ørstavik
authors.affiliation: Norwegian Institute of Public Health, Oslo, Norway.
authors.forename: T
authors.initials: T
authors.lastname: Nilsen
authors.affiliation: Norwegian Institute of Public Health, Oslo, Norway.
authors.forename: Ó A
authors.initials: ÓA
authors.lastname: Steingrímsdóttir
authors.affiliation: Australian Centre of Excellence in Twin Research, Centre for Epidemiology & Biostatistics, University of Melbourne, Melbourne, Australia; Arthritis and Musculoskeletal Research Group, Faculty of Health Sciences, University of Sydney, Sydney, Australia.
authors.forename: P
authors.initials: P
authors.lastname: Ferreira
authors.affiliation: Department of Orthopaedic Surgery, Haukeland University Hospital, Bergen, Norway.
authors.forename: A M
authors.initials: AM
authors.lastname: Fenstad
authors.affiliation: Department of Orthopaedic Surgery, Haukeland University Hospital, Bergen, Norway; Department of Clinical Medicine, Institute of Medicine and Dentistry, University of Bergen, Norway.
authors.forename: O
authors.initials: O
authors.lastname: Furnes
authors.affiliation: National Advisory Unit on Rehabilitation in Rheumatology, Department of Rheumatology, Diakonhjemmet Hospital, Oslo, Norway.
authors.forename: K B
authors.initials: KB
authors.lastname: Hagen
mesh_terms: D000328:Adult; D000359:Aftercare; D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip / Q000706:statistics & numerical data; D019645:Arthroplasty, Replacement, Knee / Q000706:statistics & numerical data; D015331:Cohort Studies; D004200:Diseases in Twins / Q000235:genetics / Q000601:surgery*; D005260:Female; D006801:Humans; D016247:Information Storage and Retrieval; D008297:Male; D008875:Middle Aged; D009664:Norway; D015207:Osteoarthritis, Hip / Q000235:genetics / Q000601:surgery*; D020370:Osteoarthritis, Knee / Q000235:genetics / Q000601:surgery*; D011446:Prospective Studies; D012042:Registries; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic
keywords: Arthroplasty; Heritability; Osteoarthritis; Twins