Archives of Osteoporosis

, 9:191 | Cite as

Impact of comorbidity, age, and gender on seasonal variation in hip fracture incidence. A NOREPOS study

  • Siri M. SolbakkenEmail author
  • Jeanette H. Magnus
  • Haakon E. Meyer
  • Nina Emaus
  • Grethe S. Tell
  • Kristin Holvik
  • Guri Grimnes
  • Siri Forsmo
  • Berit Schei
  • Anne Johanne Søgaard
  • Tone K. Omsland
Original Article



Based on a total of 136,140 hip fractures, we found a distinct seasonal variation in hip fracture incidence present in subgroups defined by age, gender, and comorbidity. The seasonal variation was most pronounced in the youngest and the healthiest patients.


The purpose of this study was to examine the possible seasonal variation in hip fracture incidence in Norway by comorbidity, age, and gender.


Data were retrieved from the NOREPOS Hip Fracture Database containing all hip fractures in Norway during the time period 1994–2008. Hip fractures were identified by computerized hospital discharge diagnoses. Charlson comorbidity index was calculated based on additional diagnoses and categorized (0, 1, and ≥2). Summer was defined as June, July, and August and winter as December, January, and February. Incidence rate ratios for hip fracture according to season were calculated by negative binomial models.


In patients aged 50–103 years, 136,140 eligible fractures were identified (72.5 % women). The relative risk of hip fracture in winter versus summer was 1.40 (95 % confidence interval (CI) 1.36–1.45) in men and 1.26 (95 % CI 1.23–1.28) in women. June had the lowest number of fractures in both genders. We found seasonal variation in all subgroups by age and gender, although least pronounced in patients >79 years. There was a significant interaction between season and comorbidity (p = 0.022). When comparing winter to summer, we found relative risks of 1.40 (95 % CI 1.31–1.50) in patients with Charlson index = 0, 1.29 (95 % CI 1.19–1.40) in patients with Charlson index = 1, and 1.18 (95 % CI 1.08–1.28) in patients with Charlson index ≥2.


There was a distinct seasonal variation in hip fracture incidence, present in all subgroups of gender, age, or comorbidity. This variation should be accounted for when planning health-care services.


Hip fracture Incidence Seasonal variation Comorbidity Age Gender 


Conflict of interest



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Copyright information

© International Osteoporosis Foundation and National Osteoporosis Foundation 2014

Authors and Affiliations

  • Siri M. Solbakken
    • 1
    Email author
  • Jeanette H. Magnus
    • 1
  • Haakon E. Meyer
    • 1
    • 2
  • Nina Emaus
    • 3
  • Grethe S. Tell
    • 4
  • Kristin Holvik
    • 2
    • 4
  • Guri Grimnes
    • 5
  • Siri Forsmo
    • 6
  • Berit Schei
    • 6
    • 7
  • Anne Johanne Søgaard
    • 2
  • Tone K. Omsland
    • 1
  1. 1.Institute of Health and Society, Department of Community MedicineUniversity of OsloBlindernNorway
  2. 2.Division of EpidemiologyNorwegian Institute of Public HealthOsloNorway
  3. 3.Department of Health and Care SciencesUiT The Arctic University of NorwayTromsøNorway
  4. 4.Department of Global Public Health and Primary CareUniversity of BergenBergenNorway
  5. 5.Department of Clinical MedicineUiT The Arctic University of NorwayTromsøNorway
  6. 6.Institute of Public Health and General Practice, Faculty of MedicineNorwegian University of Science and Technology (NTNU)TrondheimNorway
  7. 7.Department of Obstetrics and GynecologySt. Olav’s University HospitalTrondheimNorway

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