title: Seasonal variation in adult hip disease secondary to osteoarthritis and developmental dysplasia of the hip.
abstract: OBJECTIVE
  To determine if there was a seasonal variation in adults undergoing total hip arthroplasty for end stage hip disease due to osteoarthritis (OA) or sequelae of developmental dysplasia of the hip (DDH).
  
  
  METHODS
  The total hip registry from the author's institution for the years 1969 to 2013 was reviewed. The month of birth, age, gender, and ethnicity was recorded. Differences between number of births observed and expected in the winter months (October through February) and non-winter mo (March through September) were analyzed with the χ2test. Detailed temporal variation was mathematically assessed using cosinor analysis.
  
  
  RESULTS
  There were 7792 OA patients and 60 DDH patients who underwent total hip arthroplasty. There were more births than expected in the winter months for both the DDH (P< 0.0001) and OA (P= 0.0052) groups. Cosinor analyses demonstrated a peak date of birth on 1stOctober.
  
  
  CONCLUSIONS
  These data demonstrate an increased prevalence of DDH and OA in those patients born in winter.
authors.affiliation: Tatsuya Sueyoshi, Department of Orthopedic Surgery, Kyoto University, Kyoto 606-8507, Japan.
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Sueyoshi
authors.affiliation: Tatsuya Sueyoshi, Department of Orthopedic Surgery, Kyoto University, Kyoto 606-8507, Japan.
authors.forename: Merrill A
authors.initials: MA
authors.lastname: Ritter
authors.affiliation: Tatsuya Sueyoshi, Department of Orthopedic Surgery, Kyoto University, Kyoto 606-8507, Japan.
authors.forename: Kenneth E
authors.initials: KE
authors.lastname: Davis
authors.affiliation: Tatsuya Sueyoshi, Department of Orthopedic Surgery, Kyoto University, Kyoto 606-8507, Japan.
authors.forename: Randall T
authors.initials: RT
authors.lastname: Loder
keywords: Birth month; Developmental hip dysplasia; Osteoarthritis; Seasonal trend; Winter