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Daily number of fractures is associated with road temperature in an urban area

Christopher Jantzen1, Henrik L. Jørgensen2, Morten T. Thomsen1, Troels Riis1, Bo Sommer3, Benn R. Duus1 & Jes B. Lauritzen1,

1. mar. 2014
13 min.

Faktaboks

Fakta

Seasonal variation influences the incidence of fractures, which are more common during winter than during summer [1-4]. The seasonality is evident for different types of fractures including fractures of the ankle, arm and forearm [4, 5], whereas the literature on hip fractures is inconsistent with some [1-3], but not all [6-8] studies reporting seasonal variation. Different environmental factors associated with winter may explain this seasonal increase. As such, an increased incidence is found on days with adverse weather and with the presence of wintery road conditions [1, 4, 9-11]. Another component of seasonality could be the lower ambient temperature during winter, but the literature is inconclusive with some authors reporting a correlation between temperatures and incidences [1, 3], whereas others do not [6, 12]. Whereas many studies have explored the effect of seasonality, weather, road conditions and ambient temperature on fracture incidence, little is known about the association with road surface temperature. The purpose of this study was to examine the association between road surface temperature and the daily number of fractures treated in a trauma unit in an urban area for a period of two winters.

MATERIAL AND METHODS

Patients

Bispebjerg Hospital, Denmark, has a busy trauma unit with a catchment population of approximately 400,000. We retrospectively collected data on all patients treated for a musculoskeletal lesion in our trauma unit during the two winter periods from October to April 2009/2010 and 2010/2011. The data included age, gender and lesion-type. Head injuries and spine injuries together with multi-trauma patients are either admitted to other sections of the hospital or redirected to other trauma units and are therefore not included in this study. The included patients were divided into fractures and other lesions, with the latter being excluded. Fractures were divided into the following subgroups: humeral, ankle, distal radius and hip fractures. Patients were furthermore grouped according to age into the following age groups: < 15, 15-30, 30-45, 45-60 and > 60 years.

Road condition data

Data on road surface temperature (Tp.) in the catchment area during the two periods were obtained from The Danish Road Directorate. Data were grouped into the following categories: Days with Tp. > 0 °C, Tp. < 0 °C, Tp. > –5 °C, Tp. < –5 °C and ice alert (IA), the latter being triggered by a combination of low temperature and the presence of high humidity. For the purpose of analysis, the temperatures of a given day were grouped according to one of the above-mentioned categories if at any time during the day, it dropped below the limit of that category. A more detailed description of the data can be obtained from the authors. The Danish Road Directorate collects data through a number of measuring stations spread around the catchment area. These register the road- and ambient temperature together with the humidity on a five-minute basis, and it is therefore possible to continuously monitor the temperature and the humidity of the surface of the roads. Registration of road surface temperature is conducted by a temperature sensor usually placed in the wheel track at one of the driving lanes. The sensor is placed in a small hole with the sensor top located at par with the road surface. The sensor is connected to the measurement station by the roadside by wires milled a few centimetres into the pavement.

Statistical analysis

The number of fractures per day was not normally distributed. To test for differences in the daily number of fractures as a function of road conditions, non-parametric methods were therefore used (Mann-Whitney U tests) with a p-value < 0.05 considered statistically significant. The same test was used for calculating the association between road temperature and the daily number of fractures in the different age groups.

The study was approved by the Danish Data Protection Agency.

Trial registration: not relevant.

RESULTS

A total of 4,892 patients who had suffered a total of 4,938 fractures were treated during the two periods (Table 1). The daily number of humeral, ankle and distal radius fractures varied significantly with road surface temperature, whereas hip fractures were unaffected (Table 2). Age was also found to influence the daily number of fractures with decreasing road temperatures being significantly associated with an increase in fractures among patients > 30 years of age (Table 3). For patients < 15 years of age, an inverse pattern was seen with a significant decrease at Tp. < 0 °C and a non-significant decrease at Tp. < –5 °C. On days with IA, the number of fractures was found to increase significantly for patients > 30 years, whereas it decreased insignificantly for patients < 30 years.

DISCUSSION

In our study, we found that decreasing road temperature and the presence of IA was associated with an increase in the daily number of all fracture types except hip fractures. It has previously been shown that the incidence of fractures varies with the season, with greater occurrences of fractures during winter [1-4]. This may be explained by different conditions related to this time of the year. As such, cold, inclement, snowy and icy weather, low ambient temperature and snowy/icy roads are all associated with an increased fracture incidence [1, 4, 9-11], indicating that the aetiology of the winter excess is multi-factorial. We found that decreasing road temperatures were associated with an increase in daily number of ankle, distal radius and humeral fractures, but not hip fractures. Similarly, other studies have shown no influence of season [5, 6], ambient temperature [6, 12] and weather conditions [9] on the occurrence of hip fractures. This lacking correlation may be due to the fact that hip fractures more frequently occur indoors [13], consequently the incidence is consequently less affected by outdoor conditions. Supporting the importance of outdoor factors, Bergstrom et al [14] reported seasonal variation for hip fractures occurring indoor but not outdoor, and Oyen et al [15] showed a lack of seasonality for distal radius fractures occurring indoors. Likewise, distal radius fractures are more frequent among active individuals who are more likely to be outdoors [11]. Overall, this indicates that outdoor conditions contribute to the increased risk during winter. In line with this, we found that the number of all fracture types, except hip fractures, increased significantly on days with IA. This indicates that under-foot conditions, such as slippery pavement, can affect the risk of incurring such fractures. Other studies have also shown that snowy/icy road and weather conditions increase the risk of fracture [9, 10]. While slipping seems an obvious and simple reason for the increased incidence during winter, not all agree on this. Jacobsen et al [2] suggested that other variables than under-foot conditions are responsible for the excess incidence during winter. In support of this, Douglas et al [16] found seasonal variation for hip fractures in both Scotland, Hong Kong and New Zealand even though Hong Kong is without snow and ice during the winter season. Other suggested aetiological mechanisms include: 1. Hypothermia and undernutrition [17]; 2. Impaired bone quality during winter [18]; 3. Decreased muscle strength due to vitamin-D deficiency [19].

Regarding age, we found that patients in the groups > 30 years experienced a significant increase in the daily number of fractures at lower temperatures and with the presence of IA. For patients 15-30 years of age, decreasing road surface temperature and IA were insignificantly associated with a decrease in the number of fractures. In the group < 15 years, an inverse pattern was detected with a significant decrease in the number of fractures when comparing days with Tp. > 0 °C and < 0 °C. When comparing days with Tp. > –5 °C and < –5 °C, an insignificant decrease were found and this was also evident on days with IA. This inverse pattern for patients < 15 years has earlier been shown for distal radius fractures [20]. In this study, higher rates of fractures were found during summer than during winter, a possible explanation being better weather encouraging outdoor activities and thus an increased risk of accidents and fractures. As such, decreasing road temperatures during winter seems to be a risk factor for patients > 30 years and a protective factor for patients < 15 years, whereas IA is only a risk factor for patients > 30 years. It is important to remember that we only looked at the daily number of fractures in the different age groups and did not take into account the population at risk.

Due to this, direct comparison between the different groups is not possible and the results only serve to show whether decreasing road surface temperature and IA are associated with an increase in the daily number of fractures in the groups.

Limitations of our study include the retrospective data collection. Also, fractures occurring indoors are not excluded since it is not possible with the available data to differentiate between these and fractures occurring outdoors. Furthermore, since we examined an urban population, our results cannot be applied to the general population. There is also a small possibility that patients suffering a fracture in our catchment area are admitted to other hospitals, in which case the number of fractures would have been underestimated. Regarding data on road surface temperature, days were grouped according to the lowest temperature registered at any time during the day and not the mean temperature, and this could also result in an underestimation of the effect of the temperature. The most important strengths of this study are the large number of consecutive patients included together with the method and precision by which data were collected.

CONCLUSION

The aetiology of the excess fracture incidence during winter is multi-factorial. The present study highlights the effect of road surface temperature. Decreasing temperature and the presence of IA is associated with an increased number of all fracture types except hip fractures. Decreasing road temperature seems to be a risk factor for patients > 30 years of age and a protective factor for patients < 15 years of age, whereas IA is only a risk factor for patients > 30 years. These results may have implications for the prevention of accidents and the planning of staff in trauma units and orthopaedic wards. Since this is the first study examining the effect of road temperature, larger prospective studies are needed to confirm these findings.

Correspondence: Christopher Jantzen, Ortopædkirurgisk Afdeling, Bispebjerg Hospital, Bispebjerg Bakke 23, 2400 Copenhagen NV, Denmark. E-mail: christopherjantzen@gmail.com

Accepted: 2 January 2014

Conflicts of interest:Disclosure forms provided by the authors are available with the full text of this article at www.danmedj.dk

Referencer

REFERENCES

  1. Levy AR, Bensimon DR, Mayo NE et al. Inclement weather and the risk of hip fracture. Epidemiology 1998;9:172-7.

  2. Jacobsen SJ, Goldberg J, Miles TP et al. Seasonal variation in the incidence of hip fracture among white persons aged 65 years and older in the United States, 1984-1987. Am J Epidemiol 1991;133:996-1004.

  3. Modarres R, Ouarda TB, Vanasse A et al. Modeling seasonal variation of hip fracture in Montreal, Canada. Bone 2012;50:909-16.

  4. Bischoff-Ferrari HA, Orav JE, Barrett JA et al. Effect of seasonality and weather on fracture risk in individuals 65 years and older. Osteoporos Int 2007;18:1225-33.

  5. Weston-Simons J, Jack CM, Doctor C et al. The impact of snow on orthopaedic trauma referrals. Injury 2012;43:1033-6.

  6. Chesser TJ, Howlett I, Ward AJ et al. The influence of outside temperature and season on the incidence of hip fractures in patients over the age of 65. Age Ageing 2002;31:343-8.

  7. Aharonoff GB, Koval KJ, Skovron ML et al. Hip fractures in the elderly: predictors of one year mortality. J Orthop Trauma 1997;11:162-5.

  8. Parker MJ, Martin S. Falls, hip fractures and the weather. Eur J Epidemiol 1994;10:441-2.

  9. Murray IR, Howie CR, Biant LC. Severe weather warnings predict fracture epidemics. Injury 2011;42:687-90.

  10. Lauritzen JB, Schwarz P, McNair P et al. Radial and humeral fractures as predictors of subsequent hip, radial or humeral fractures in women, and their seasonal variation. Osteoporos Int 1993;3:133-7.

  11. Graafmans WC, Ooms ME, Bezemer PD et al. Different risk profiles for hip fractures and distal forearm fractures: a prospective study. Osteoporos Int 1996;6:427-31.

  12. Tenias JM, Estarlich M, Fuentes-Leonarte V et al. Short-term relationship between meteorological variables and hip fractures: an analysis carried out in a health area of the Autonomous Region of Valencia, Spain (1996-2005). Bone 2009;45:794-8.

  13. Carter SE, Campbell EM, Sanson-Fisher RW. Accidents in older people living at home: a community-based study assessing prevalence, type, location and injuries. Aust N Z J Public Health 2000;24:633-6.

  14. Bergstrom U, Bjornstig U, Stenlund H et al. Fracture mechanisms and fracture pattern in men and women aged 50 years and older: a study of a 12-year population-based injury register, Umea, Sweden. Osteoporos Int 2008;19:1267-73.

  15. Oyen J, Rohde GE, Hochberg M et al. Low-energy distal radius fractures in middle-aged and elderly women-seasonal variations, prevalence of osteoporosis, and associates with fractures. Osteoporos Int 2010;21:1247-55.

  16. Douglas S, Bunyan A, Chiu KH et al. Seasonal variation of hip fracture at three latitudes. Injury 2000;31:11-9.

  17. Bastow MD, Rawlings J, Allison SP. Undernutrition, hypothermia, and injury in elderly women with fractured femur: an injury response to altered metabolism? Lancet 1983;1:143-6.

  18. Rosen CJ, Morrison A, Zhou H et al. Elderly women in northern New England exhibit seasonal changes in bone mineral density and calciotropic hormones. Bone Miner 1994;25:83-92.

  19. Schott GD, Wills MR. Muscle weakness in osteomalacia. Lancet 1976;1:626-9.

  20. Wareham K, Johansen A, Stone MD et al. Seasonal variation in the incidence of wrist and forearm fractures, and its consequences. Injury 2003;34:219-22.