title: Neonatal hip instability and risk of total hip replacement in young adulthood: follow-up of 2,218,596 newborns from the Medical Birth Registry of Norway in the Norwegian Arthroplasty Register.
abstract: OBJECTIVE
  Dysplasia is probably the most common underlying condition in osteoarthritis of the hip, leading to total hip replacement (THR) in young adulthood. We investigated whether hip instability at birth predisposes to THR in young adulthood.
  
  
  METHODS
  Since 1967, all newborns in Norway have been screened for neonatal hip instability (NHI) and the results have been reported to the Medical Birth Registry of Norway (MBRN). In the period 1967-2004,2,218,596 newborns were registered. From 1987 to 2004, 442 of these individuals had been reported to the Norwegian Arthroplasty Register (NAR) after undergoing total hip replacement (mean age 25 (12-36) years).
  
  
  RESULTS
  Neonatal hip instability was reported in 19,432 newborns (0.88%) in the MBRN; according to the NAR, they had a 2.6 (CI 1.4-4.8) times increased risk of THR in young adulthood compared to those without NHI. The absolute risk was low, however; only 57 (95% CI: 30-105) in 10(5) for patients with NHI compared to 20 (95% CI: 18-22) in 10(5) for those without registered hip pathology. Of the 442 patients with THR, 95 were operated because of osteoarthritis of the hip secondary to dysplasia, according to the surgeon's report. However, only 8 of these 95 patients had been reported to have hip instability at birth.
  
  
  CONCLUSIONS
  Neonatal hip instability increases the risk of THR in young adulthood. Unexpectedly, only 8% of those who underwent THR due to dysplasia were reported to have unstable hips at birth. Our results indicate that clinical testing for NHI is insufficient as a screening method for dysplastic hips that require THR in young adulthood.
authors.affiliation: The Norwegian Arthroplasty Register, Department of Orthopaedic Surgery, Haukeland University Hospital, Unifob, Bergen. ingvild.engesater@student.uib.no
authors.forename: Ingvild Ø
authors.initials: IØ
authors.lastname: Engesaeter
authors.forename: Stein Atle
authors.initials: SA
authors.lastname: Lie
authors.forename: Trude G
authors.initials: TG
authors.lastname: Lehmann
authors.forename: Ove
authors.initials: O
authors.lastname: Furnes
authors.forename: Stein Emil
authors.initials: SE
authors.lastname: Vollset
authors.forename: Lars B
authors.initials: LB
authors.lastname: Engesaeter
mesh_terms: D000293:Adolescent; D000328:Adult; D019644:Arthroplasty, Replacement, Hip; D002648:Child; D005260:Female; D006618:Hip Dislocation, Congenital / Q000150:complications* / Q000175:diagnosis / Q000000981:diagnostic imaging; D006621:Hip Joint / Q000503:physiopathology; D006801:Humans; D007231:Infant, Newborn; D007593:Joint Instability / Q000150:complications*; D008297:Male; D015997:Neonatal Screening; D009664:Norway; D015207:Osteoarthritis, Hip / Q000209:etiology* / Q000601:surgery; D011336:Probability; D012042:Registries; D012307:Risk Factors; D014463:Ultrasonography