Kristin K Clemens, MD, MSc1,2,3,4, Alexandra Ouedraogo, MSc2, Mark Speechley, PhD3,4, Lucie Richard, MSc2, Jenny Thain, MD5, Salimah Z Shariff, PhD2
1Department of Medicine, Division of Endocrinology, Western University, London, ON, Canada
2ICES, ON, Canada
3Lawson Health Research Institute, London, ON, Canada
4Department of Epidemiology and Biostatistics, Western University, London, ON, Canada
5Department of Medicine, Division of Geriatrics, Western University, London, ON, Canada
DOI: https://doi.org/10.5770/cgj.22.341
ABSTRACT
Background
In older adults, hip fractures have been described to peak in cooler months. Seasonal differences in patient vulnerability to fracture and social/behavioural factors might contribute to these trends.
Methods
Using linked health-care databases in Ontario Canada, we examined monthly variation in hip fracture hospitalizations in those > 65 years (2011–2015). We stratified results by age category (66–79, ≥80 years). We then examined for variation in the demographic and comorbidity profiles of patients across the months, and as an index of contributing social/behavioural factors, noted variation in health-care behaviours.
Results
There were 47,971 and 52,088 hospitalizations for hip fracture in those 66–79, and ≥80 years, respectively. There was strong seasonality in fractures in both groups. Peaks occurred in October and December when patients appeared most vulnerable. Rates fell in the summer in those 66–79 years, and in the late winter in those ≥80 years (when health-care utilization also declined). A smaller peak in fractures occurred in May in both groups.
Conclusions
Hip fractures peak in the autumn, early winter, and spring in Canada. A dip in fractures occurs in the late winter in the oldest old. Environmental factors might play a role, but seasonal vulnerability to fracture and winter isolation might also be influential.
Key words: hip fractures, trends, variation, elderly
Hip fractures can have catastrophic outcomes for older adults. (1) They lead to pain, loss of function, institutionalization, and even death.(2,3) With our aging population, hip fractures will continue to be a population health problem.
In Canada, there have been increased efforts to both prevent and improve the care and outcomes of patients with hip fractures.(4,5) In this setting, a thorough understanding of the risk factors for these fractures remains important.
The seasonality of health outcomes can provide insights about the etiology of disease, as well as help care professionals and policy makers anticipate and prepare for outcomes.(6) Where seasonal trends in hip fractures have been described across geographic regions previously, peaks were observed in cooler months.(7–9) Slippery surfaces due to freezing temperatures, and vitamin D deficiency due to lack of sunlight, have been proposed as contributors to these trends.(7,9–11) However, non-weather factors might also partly explain hip fracture trends. People might be more vulnerable to falls at different times of year due to underlying illness or comorbidities such as infections. Seasonal variation in fracture rates might also be driven by temporal differences in social or behavioural factors.(6) Patients, for example, might avoid or be unable to receive health care during particular times of the year (e.g., the holidays),(12) which could impact their susceptibility to health outcomes. Additionally, if people travel outside a region at different times of the year (i.e., seasonal migration from cold to warm climates),(12) their fractures might not be ascertainable in research studies.
There has been no recent evaluation of monthly variation in hip fractures in older adults in Canada. In the current study we provide an updated assessment of fracture trends in those >65 years in the province of Ontario. We hypothesized that hip fractures would be most common during the cooler months. To examine potential reasons for seasonal variation in hip fractures, we ascertained the demographic characteristics and comorbidity profiles of patients with fractures over the months. To determine whether social or behavioural factors might influence fracture trends, we also examined variations in health-care utilization including visits to health-care professionals, blood tests, and prescription medication dispensing.
We conducted a population-based study of adults age >65 years in Ontario, Canada from January 1 2011 until December 31 2015. We divided our study period into one-month intervals.
Ontario is a northern region between the 42nd and 57th latitudes, with cold winters and subzero temperatures. We have over 13 million residents who have universal coverage for hospitalizations, physician visits, and diagnostic testing. (13) People aged ≥65 years have universal access to prescription medications. Information on their health-care utilization is maintained in databases held at ICES. Databases are linked using unique, encoded identifiers. We report our study using the RECORD recommendations (Appendix A).(14)
Our study was approved by the research ethics board at Sunnybrook Health Sciences Centre (Toronto, Ontario) and was analyzed at ICES according to a pre-specified protocol. Participant consent was not necessary as ICES is a named entity under Ontario’s Personal Health Information Protection Act, and is able to receive and use health information to examine the province’s health-care system.
We considered for inclusion all adults >65 years with a hospitalization for a hip fracture over the study period (defined as at least one code for a hip fracture during an inpatient hospital stay). Our coding algorithm for hip fracture included diagnostic and medical billing codes,(15) similar to one validated previously (positive predictive value 83%, sensitivity 99%) (16) (Appendix B).
Prior to each study interval, we excluded the records of those: 1) with a missing age, sex or an invalid identification number, 2) an extreme or invalid age (negative age or age >105), 3) who died on or before the study interval, or 4) who were not permanent residents of Ontario (i.e., did not have an Ontario residential postal code at the time of hospitalization). If patients had more than one encounter for a hip fracture over the study interval (i.e., month), we included only their first hospitalization.
We used the records of several databases as our data sources. A full description of each database is included in Appendix C. In brief, the Registered Persons Database of Ontario provided demographic information for people who had been issued an Ontario health card. We used the Yearly Ontario Intercensal and Postcensal Population Estimates and Projection database to determine population denominators (Ontario Ministry of Health and Long-Term Care: IntelliHEALTH Ontario). We used the Ontario Drug Benefit (ODB) and the Drug Identification Number (DIN) databases to ascertain prescription medications. Prescription records are accurately maintained within the ODB with an error rate < 1%.(17) We assessed baseline comorbidities using the Ontario Diabetes Database (ODD),(18) the Ontario Chronic Obstructive Pulmonary Disease,(19) Rheumatoid Arthritis,(20) and Crohn’s and Colitis Datasets.(21) Home care visits were captured using the Home Care Database, and physician visits were ascertained using the ICES Physician Database. We used the Canadian Institute for Health Information’s Discharge Abstract Database (CIHI-DAD) and the National Ambulatory Care Reporting System (NACRS) Database to collect diagnostic and procedural information captured during hospital admissions and emergency department visits, respectively. We additionally used the Ontario Health Insurance Plan (OHIP) Database to capture patient diagnoses and procedures.
Covariates and outcomes were ascertained by a patient’s presence in a derived database (e.g., the ODD), or administrative codes (Appendix D). Administrative codes are entered into databases including the CIHI-DAD and NACRS by trained personnel, based upon diagnoses recorded in the medical record by the health-care team. We used International Classification of Diseases 10th Revision (ICD-10), the enhanced Canadian version of the 10th Revision of the International Statistical Classification of Diseases and Related Health Problems (ICD-10 CA), Canadian Classification of Health Interventions (CCI, post-2002), and OHIP fee and diagnostic codes.
Our primary outcome was monthly variation in hip fracture hospitalizations in those >65 years. Because the risk of osteoporosis and hip fracture is highest in the oldest old (i.e., ≥80 years),(22) we stratified trends by age group (i.e., 66–79, ≥80 years).
We performed several additional analyses. We noted monthly variation in the demographic characteristics, comorbidity profiles, and health-care utilization of patients with fractures between September 2012 and August 2013 (study midpoint). We also examined trends in prescription medication dispensing for statins, as statins are the most commonly prescribed medication to older adults in Canada.(23) Finally, to evaluate if seasonality in hip fractures might be due to older adults leaving our region over particular months of the year (i.e., ‘snowbirding’),(24) we examined monthly variation in travel supplies for statins (i.e., a prescription dispensed for >100 tablets), over the study period.(25)
Numerators were the number of patients with at least one hospital encounter with a hip fracture over the study period, stratified by age. Denominators for all months were the estimated population of Ontario on July 1st of the relevant year in the age strata. To consider population changes over time, we calculated monthly encounter rates and their associated 95% confidence intervals (CI).
Based upon prior methods,(6) we used time series analyses to assess for seasonality in hip fractures, as well as the strength of the relationship. We first visualized the raw data and then fitted regression lines to detect trends. We then used differencing methods to ensure data stationarity. Next, we used spectral analyses to detect statistically significant seasonality, the Fisher Kappa Test to determine if there was a major sinusoidal component, and the Bartlett Kolmogorov Smirnov Test to examine departures from the null hypothesis of pure white noise. We also examined spectral plots of the data (i.e., spectral density vs. data frequency) to identify the cyclic structure of the series, and we conducted multitaper spectral analyses. To examine the strength of the seasonal relationships, we generated R2 autoregression coefficients, which are the coefficients of determination of the autoregressive regression models fitted to the data. Coefficients of 0 to < 0.4 represent weak seasonality, 0.4 to < 0.7 moderate to strong, and 0.7 to 1 very strong to perfect seasonality.(6,26)
We used descriptive statistics to summarize the characteristics, comorbidities, and health-care patterns of patients with a hip fracture from September 2012 until August 2013. If they had more than one encounter that year, we ascertained characteristics at the time of their first encounter only. We used Chi-squared analyses, one-way ANOVA, and Kruskal-Wallis tests to examine differences in covariates across the calendar months. For our prescription dispensing analysis, numerators were the number of patients 66–79 and ≥80 years with at least one statin prescription during the study interval, and denominators were the estimated population on July 1st of the relevant year in the age strata. We calculated monthly prescription rates and their associated 95% CIs. To evaluate for the possibility of snowbirding, we examined the maximum day supply of a statin per patient each month, and determined the number with a day supply of statins >100 days. The denominator for this analysis was the total number of people who filled a statin prescription within the calendar year, across the two age groups. All analyses were conducted in SAS version 9.4 (SAS Institute, Inc., Cary, NC).
Prior to each study interval, we excluded 12–51 (0.5–2.2%) records based upon an invalid identification number or sex, 141–220 (5.8–9.5%) records that had an invalid age, <6 records with a death recorded on or before the study interval, and <6 records for those who were not permanent residents of Ontario.
We included a total of 47,971 and 52,088 hip fracture hospitalizations in those 66–79 and ≥80 years between 2011–2015 in Ontario, Canada (42,694 and 47,648 unique patients, respectively).
Hip fracture rates appeared stable over time across groups. Strong seasonality was apparent in both age groups (Table 1). Fractures peaked in October and December, with a smaller peak in May. In those ≥80 years, fractures fell to a minimum in February. Fracture rates appeared to drop to a minimum in August in those 66–79 (Figure 1).
TABLE 1 Statistical summary of seasonality of hip fracture encounters
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FIGURE 1 Rates of hip fracture encounters in patients 66–79 and ≥80 years in Ontario from 2011–2015 |
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The monthly characteristics of patients with hip fractures are presented in Tables 2 and 3. Compared with those who fractured during other months, patients with an autumn and winter fracture were more likely to have experienced a fall or fracture in the year prior. Those who were 66–79 years also appeared to have more comorbidities (i.e., higher Charlson comorbidity index), and used more unique medications than those who fractured at other times of the year.
TABLE 2 Characteristics of patients aged 66–79 with hip fractures from September 2012 to August 2013 (N=9014)
TABLE 3 Characteristics of patients aged 80+ with hip fractures from September 2012 to August 2013 (N=10,096)
The health-care utilization of patients varied monthly. Primary care visits appeared less frequent across groups in the late winter and, in the oldest old, blood tests and specialist visits also appeared slightly less frequent (Tables 2 and 3). Statin prescription rates declined across both age groups in the late winter (Figure 2). Both groups showed evidence of snowbirding over the winter months (i.e., higher rate of travel prescription fills in the late fall), but this appeared more common in those 66–79 years than in the oldest old (Figure 3).
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FIGURE 2 Statin prescription rates per 100 people aged 66–79 and ≥80 in Ontario |
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FIGURE 3 Rate of statin prescriptions with greater than 100 days supply per 10,000 people in Ontario, categorized by age groups, 66–79 and ≥80 years |
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In older adults in Ontario, hip fractures are most common in the late autumn, early winter, and spring. In the oldest old, hip fracture rates appeared lowest in the late winter.
As previously suggested, environmental factors might contribute to these trends. With exposure to ice and snow in the early winter (perhaps more so during the holidays),(8,27,28) older people might be predisposed to slips and falls. A systematic review of studies that examined the association between hip fractures and at least one weather variable across 18 locations found that snow and ice were positively correlated with hip fractures at all latitudes.(7) As hip fractures also peak in regions with no ice or snow,(29,30) colder temperatures (especially the acute lowering of temperature) might also contribute to monthly variation. When exposed to the cold, people might experience hypothermia and poor coordination. They might also dress in layers which could lead to trips and falls.(7) An acute drop in temperature from a warmer summer to a cooler autumn might have contributed to the fracture peak we saw in October, especially if people had not yet adapted to the temperature change.(31)
Vitamin D deficiency could have also contributed to fracture trends.(8,10,11,32) Vitamin D is typically lowest at the end of the winter when parathyroid hormone is high.(10) During winter months, bone turnover also increases and bone density declines.(11,33) These changes might have predisposed individuals to fracture. Vitamin D deficiency can also impair muscle strength and coordination.(34) A darker winter might have also impaired visual acuity.(35)
Beyond environmental influences, we found evidence that patient characteristics, comorbidities, and social/behavioural factors might contribute to hip fracture trends in older adults. Older adults who had a fracture appeared to be in poorer health in the autumn and winter. During these seasons, infections are more common,(6) and patients might have been predisposed to falls and fracture while they were ill.
Respiratory illnesses peak in the spring in the older age groups,(36) when we noted a second peak in fracture rates. This peak might have also been due to people becoming active again outside. In our study, people who had a hip fracture in the spring appeared healthier than those who fractured at other times of the year. Previous studies have noted that healthy active people are at higher risk of outdoor falls while engaging in vigorous activities.(37,38)
Of particular interest, we observed that in the oldest old, fractures appeared less common in the late winter. During the late winter it is coldest in Canada(39) and older adults might simply avoid the outdoors, especially if they have comorbidities, are immobilized, or institutionalized.(9,40,41) Aligned with this, their health care utilization also appeared to decline with fewer primary care visits and a lower rate of prescription medication dispensing. Although there was evidence of snowbirding in both age groups, the trend seemed most apparent in those 66–79 years. This trend wouldn’t sufficiently explain the decline in health-care utilization in the oldest old, suggesting that older seniors might avoid going outside during the late winter.
Hip fractures have been described to peak in the autumn and winter in older Canadian studies from Montreal.(9,27) Outside of Canada, in a Spanish study of people >45 years (mean age 80 years), there was also an increased risk of fracture during these months.(29) Similar trends have been described in Taiwan,(8) as well as across the United States,(42) Israel,(28) Scotland, Hong Kong, New Zealand,(30) and Norway.(43)
The decline in fractures in those ≥80 in the late winter has not been thoroughly described. While most studies note a trough in fracture rates over the summer months,(41,44) our extreme winter climate where temperatures can drop below −30°C in areas, might partly explain our findings.
There are several strengths to the current study. It is a large, up-to-date, population-based study of 100,059 hip fracture encounters (89,913 unique individuals) in our province over a five-year period. Rather than simply describing fracture variation, we evaluated trends within two age strata, and examined variation in patient comorbidities and health services utilization.
There are some limitations to discuss. We could not exclude high-velocity fractures (i.e., from motor vehicle collisions) or pathological hip fractures, although it is estimated that over 95% of hip fractures are due to a fall.(45) We also included procedural codes for hip fractures, and thus, double counting of encounters could have occurred. However, we minimized this risk by limiting to one hip fracture encounter per month. We used administrative data to ascertain our outcomes and this data were not specifically created to address our research question. However, our data can minimize the bias associated with self-report and surveys.(16) Changes in coding definitions might have occurred over the study period and may have affected our temporal trend analyses. We also could not determine the location of the hip fractures (i.e., indoors vs. outdoors). Our study population also included a mix of both community and long-term care residents.
Due to the size and duration of our study, we were only able to ascertain the characteristics and comorbidities of patients over one year. We were unable to evaluate factors, including frailty and balance, which can impact fracture risk. Importantly, this was an ecological study and we cannot infer causation at an individual level. Our results are only fully generalizable to those living in Ontario.
Our study has implications for practice, policy, and research. First, given the possible link between hip fractures and environmental factors, patients should be advised to be cautious while traversing snow and ice, and to wear proper footwear. (46) Even if indoors during the cooler months, they might be warned of tripping hazards, especially when layering for the colder weather. When people are in poorer health, they might be cautioned about the risk of falls. Further, physicians might replace vitamin D and ensure adequate calcium intake during the winter months, especially in the frail and institutionalized. (34,47,48) A role for UV light exposure in the winter has also been suggested.(8)
From a policy standpoint, health administrators might plan resources accordingly. Operating times for hip fractures might be opened in the cooler seasons, and hospitals might be prepared for more consultations. Awareness of fracture peaks might promote timely assessments and treatment.(4) Troughs in fracture rates and health services utilization over the winter might raise the possibility of social isolation; as a result, ensuring that home-based resources are available might be of importance (e.g., home care services, exercise programs, food delivery). This might be especially needed by those who are too frail to leave their residence.(35) For city workers and planners, timely ice and snow removal also remains important.(35)
Finally, from a research perspective, researchers might better consider snowbirding when conducting trend analyses, to ensure accurate denominators.
In our region, the oldest old have a unique pattern of hip fracture hospitalizations across the months. Beyond environmental influences, complex patient, social, and behavioural factors might contribute to observed trends.
This project was conducted at ICES Western, and was funded by an Innovations Grant from the Academic Medical Organization of Southwestern Ontario (AMOSO). ICES is funded by an annual grant from the Ontario Ministry of Health and Long-term Care (MOHLTC). Core funding for ICES Western is provided by AMOSO, the Schulich School of Medicine and Dentistry (SSMD), Western University, and the Lawson Health Research Institute (LHRI). Parts of this material are based upon data and information compiled and provided by the Canadian Institute for Health Information (CIHI). However, the analyses, conclusions, opinions and statements expressed herein are those of the authors, and not necessarily those of CIHI.
KC received a Diabetes Canada Junior Investigator Award sponsored by Astra Zeneca. She has also attended conferences sponsored by Merck. There are no other conflicts of interest to disclose and no endorsement by ICES, AMOSO, SSMD, LHRI or the MOHLTC is intended or should be inferred.
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Canadian Geriatrics Journal, Vol. 22, No. 3, September 2019