O R I G I N A L R E S E A R C H Population-based incidence of proximal radial and ulnar fractures among adults in a Canadian metropolitan area David M. Shepsa,b, Kyle A. R. Kempb and Kevin A. Hildebrand ABSTRACT Background The lack of North American population-based incidence studies of fractures of the proximal radius and ulna creates challenges in the assessment of outcomes and corresponding complication rates. Such data may help to establish consensus regarding optimal treatments. The present study’s goal was to determine the population-based incidence of proximal radial and ulnar fractures in a large metropolitan area. Methods Over a 3-year period (April, 2002--March, 2005), cases of proximal radial and ulnar fractures were documented and classified according to the AO/OTA system. Overall, ageadjusted, age-specific, gender-specific, and fracture-specific rates were calculated according to patient demographic and 2001 Canadian census data. Rates were reported as per 10,000 persons per year. Results 1030 proximal radial and ulnar fractures were identified. Fractures occurred at an overall rate of 5.09 (95%CI: 4.78 to 5.40), while the age-adjusted incidence was 5.14 (95% CI: 5.05--5.23). The most common fracture types observed were B2.1 (simple articular fracture of radius, n ¼ 374), B1.1 (unifocal articular fracture of ulna, n ¼ 280), and A2.2 (simple extraarticular fracture of neck of radius, n ¼ 145). Fracture incidence was similar among all age groups (approximately five), with the exception of patients ages 80 years and older (8.70; 95% CI: 6.24--11.16). Males and females had similar fracture incidences at all ages. Conclusions As our results indicate similar incidences across age and gender groups, our data is likely generalizable to the general populaa Division of Orthopaedics, University of Calgary, Calgary, Alberta, Canada b Division of Orthopaedic Surgery, University of Alberta, Edmonton, Alberta, Canada Funding for this study was obtained from the University of Calgary, the Calgary Health Region, the Canadian Institutes for Health Research (CIHR), the Calgary Orthopaedic Research Education Fund, and the Calgary Surgical Research Development Fund. The authors would like to thank Sandy Doolaar, Quality Improvement and Health Information, Calgary Health Region, for her assistance with data collection for this study. Financial Disclosure: The authors report no financial and conflicts of interest. Correspondence to David M. Sheps, MD, MSc, FRCSC, 10839 124th Street NW, Edmonton, Alberta, Canada T5M 0H4 Tel: þ 780 453 2953; fax: þ 780 453 2964; e-mail: [email protected] 1940-7041 r 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins 364 Current Orthopaedic Practice tion, which may provide further insight into the assessment of outcomes and complication rates of such injuries. Keywords Canada, fracture, population-based incidence, proximal radius, proximal ulna INTRODUCTION T he study of traumatic injuries using an epidemiologic approach is an evolving process. As with various fractures of the upper limb, there are limited population-based reports on the incidence of proximal radial and ulnar fractures. As most published research does not separate proximal fractures from those occurring mid-shaft or distally,1--5 this limits the ability to calculate the true incidence of proximal radial and ulnar fractures. Additionally, previous studies have employed a variety of classification systems in the description of the type and distribution of fractures,6--13 which may introduce observer error. Because of these conflicting observations of incidence and patterns of distribution of proximal radial and ulnar fractures within the orthopaedic literature, an accurate assessment of the true epidemiology of these injuries is difficult to ascertain. As fractures of the proximal radius and ulna may result in a substantial amount of disability and subsequent functional impairment, concerted efforts to document the incidence of these fractures may improve treatment outcomes. Therefore, the goal of the present study was to determine the overall, age-adjusted, age-specific, genderspecific, and fracture-specific incidence of proximal radial and ulnar fractures over a 3-year period in a major Canadian urban center. These estimates may be used as denominators in the calculation of outcome and complication rates for specific injuries. With the application of this information, the orthopaedic community may gain a better understanding as to why such injuries do poorly, with the ultimate goal of improving treatment results. MATERIALS AND METHODS Before commencing the study, ethics approval was obtained from our institutional Research Ethics Boards (REB). The present study included proximal radial fractures, ulnar fractures, or both during a 3-year period (April, 2002--March, 2005) within a large Canadian metropolitan health region. Inpatient discharges and ambulatory care visits among individuals ages 18 years and older were included, as identified with the aid of the regional administrative database Volume 23 Number 4 July/August 2012 www.c-orthopaedicpractice.com | 365 Current Orthopaedic Practice used in the region. This database encompasses health records of patients treated in the three adult acute care hospitals, the two urgent care facilities, and the three rehabilitation hospitals within the region. These sites provide the majority of orthopaedic care and almost all of the complex orthopaedic care within the region. During the 3-year period of the study, the health region used the International Statistical Classification of Diseases and Related Health Problems, version 10 (ICD-10) coding system to record the diagnoses of patients at each site. Each case was given at least one discharge diagnosis by the treating physician most responsible for the patient’s care. The discharge diagnosis was converted to the appropriate ICD-10 code by the health records department, for inclusion in the health records database. Before conducting the database search, ICD-10 codes for proximal radial and ulnar fractures were identified. Cases captured from the database included those that contained at least one eligible ICD-10 code. To ensure that duplicate cases were not included, cases from each site were cross-referenced with all other sites, using personal health numbers, dates of service, and type of injury. Demographic data (date of birth, date of injury, gender) were collected for each case. These were used to calculate age-specific and gender-specific incidence rates and for the standardization of incidence to the Canadian population from the 2001 national census, which includes both age and gender-specific population rates.14 Each patient’s address was verified to ensure that residence was within the city under study. Patients with a residential postal code from outside of the city were excluded from review. Radiographs for each identified case were collected for review. Pretreatment radiographs also were compiled when available. For cases in which pretreatment radiographs were not available, post-treatment radiographs were compiled along with relevant patient chart documents describing the pretreatment injury. For the purpose of injury classification, two authors, both practicing upper extremity orthopaedic surgeons, reviewed the radiographs and relevant patient chart documents. Each fracture was classified using the comprehensive AO/OTA system (Table 1).15 In addition, other classification systems were applied at various fracture sites, whenever applicable. These include the Mason (radial head),6 Mayo (olecranon),16 Regan and Morrey (coronoid),17 and Bado (Monteggia).18 Statistical analysis was performed using STATA version 8.0 (STATA Corporation, College Park, TX) and SPSS version 13.0 (SPSS Inc., Chicago, IL). Confidence intervals were calculated for all incidence rates using a Poisson distribution. Standardization of the results was performed using the direct form of standardization, using the stratum-specific rates in the study population and the stratum structure (percentages) of the standard population. The age-adjusted rates were weighted averages of the age-specific rates, with the weights equal to the proportion of the Canadian population in each age category from the 2001 national census. Both the crude rates and the standardized rates are included in the results section. During the 2001 national census, the adult (18 years and older) populations of Canada and the studied city were 23,040,965 and 674,695 persons, respectively.14 TABLE 1. AO classification system for proximal radial and ulnar fractures A1 Extraarticular fracture, radius intact 1 avulsion of the triceps insertion from the olecranon 2 metaphyseal simple 3 metaphyseal multifragmentary A2 Extraarticular fracture, of the radius, ulna intact 1 avulsion of the bicipital tuberosity of the radius 2 neck simple 3 neck multifragmentary A3 Extraarticular fracture of both bones 1 simple of both bones 2 multifragmentary of one bone and simple of the other 3 multifragmentary of both bones B1 Articular fracture, of the ulna, radius intact 1 unifocal 2 bifocal simple 3 bifocal multifragmentary B2 Articular fracture, of the radius, ulna intact 1 simple 2 multifragmentary without depression 3 multifragmentary with depression B3 Articular fracture, of the one bone, with extraarticular fracture of the other 1 ulna, articular simple 2 radius, articular simple 3 articular multifragmentary C1 Articular fracture, of both bones, simple 1 olecranon and head of radius 2 coronoid process and head of radius C2 Articular fracture, of both bones, the one simple and the other multifragmentary 1 olecranon multifragmentary, radial head simple 2 olecranon simple, radial head multifragmentary 3 coronoid process simple, radial head multifragmentary C3 Articular fracture, of both bones, multifragmentary 1 three fragments of each bone 2 ulna, more than three fragments 3 radius, more than three fragments RESULTS Over the 3-year study period, a total of 1,030 patients (507 males, 523 females; mean age ¼ 43.8 ± 17.5 years) with a fracture of the proximal radius, ulna, or both were identified. The most common fracture types observed were B2.1 (simple articular fracture of radius, n ¼ 374), B1.1 (unifocal articular fracture of ulna, n ¼ 280), and A2.2 (simple extraarticular fracture of neck of radius, n ¼ 145). The overall incidence of proximal radial and ulnar fractures was 5.09 per 10,000 persons per year (95% CI: 4.78--5.40), while the age-adjusted incidence was 5.14 (95% CI: 5.05--5.23). Men and women had similar incidences (5.07 compared with 5.11, respectively). Based on the AO classification, the incidence of fracture was similar for all age groups between 18 and 79 years of age (incidences ranging 4.62--5.53). In comparison, the 80-years-old or older cohort showed an increase in incidence (8.70, 95% CI: 6.24--11.16). The complete list of age-specific, gender-specific, and age-adjusted fracture incidence rates is provided in Table 2, while fracture counts according to AO group, age, and gender are displayed in Figure 1. According to the other fracture sub-site classifications, the overall rate of Mason type-I fractures (radial head) was 2.01 per 10,000 persons per year (95% CI: 1.82--2.21). Olecranon fractures occurred at a rate of 1.12 per 10,000 persons per Volume 23 Number 4 July/August 2012 366 | www.c-orthopaedicpractice.com TABLE 2. Age, sex, and age-adjusted incidence rates of proximal radial and ulnar fractures (per 10,000 persons per Year) Group 18-29 30-39 40-49 50-59 60-69 70-79 80 þ Females Males Age-adjusted Total Incidence Rate 95% Confidence Interval 5.12 4.75 4.62 5.53 5.43 4.90 8.70 5.11 5.07 5.14 5.09 4.49--5.76 4.12--5.37 4.00--5.24 4.66--6.40 4.28--6.57 3.62--6.19 6.24--11.16 4.67--5.55 4.62--5.51 5.05--5.23 4.78--5.40 year (95% CI: 0.97--1.26), with Mayo sub-type IIa being the most common. Coronoid fractures occurred at a rate of 0.75 per 10,000 persons per year (95% CI: 0.63--0.87), while Monteggia fracture-dislocations had a rate of 0.23 per 10,000 persons per year (95% CI: 0.23--0.27). DISCUSSION To our knowledge, this study is the first comprehensive North American population-based study to present the incidence of proximal radial and ulnar fractures using expert-based classifications. Our results highlight the most common fracture types seen, as well as the similarities in rates between genders. In a previous American study, Baron et al.19 presented the population-based incidence of fractures of the proximal radius and ulna in patients between the ages of 65 and 89. However, their results were based on gender and race, and overall rates were not presented. Since the authors did not provide the population at risk, it is difficult to calculate the combined rate. As such, the authors presented rates of 1.5--8.6 per 10,000 persons per year, which compare favorably to the rates of 5.43--8.70 per 10,000 persons per year in the present study. Examining the counts and incidence rates of proximal radial and ulnar fractures separated by AO group provides some insight into the frequency of occurrence of these fractures. Group B fractures are by far the most common type, occurring at a rate more than four times that of group A fractures and more than 13 times that of group C. Within group A, the incidence rates show a similar rate of occurrence of these fractures in all age groups and in both sexes, with rates that range from 0.72--0.96 per 10,000 persons per year. The most common type in group A, type A2.2 or fractures of the radial neck, occurs in a bimodal distribution. The rates in the younger and older age groups are closer to 0.8 per 10,000 persons per year, compared with rates of 0.5 per 10,000 persons per year in the middle age groups. However, there is a significant drop-off in rates in the oldest age group (0.18 per 10,000 persons per year). This FIGURE 1. Observed fracture counts according to AO group, age and gender. Type A (RA) refers to extraarticular fractures. Type B (RB) are articular fractures of a single bone, with or without an extraarticular fracture of the other bone. Type C (RC) are articular fractures of both bones. www.c-orthopaedicpractice.com | 367 Current Orthopaedic Practice may again be attributable to the small size of this group, where an increase in one A2.2 injury would have had a dramatic affect on the incidence rate for this group. In addition, there is overlap of the confidence intervals, particularly in the older age groups. Within group B, the incidence rates are similar in all age groups at approximately four per 10,000 persons per year, with the exception of individuals age 80 and older in whom the rate almost doubles (7.25 per 10,000 persons per year). The two most common types in group B, types B1.1 (unifocal intraarticular fractures of the proximal ulna), and B2.1 (simple undisplaced and displaced fractures of the radial head) occur in opposite distribution patterns. The incidence rate of B1.1 fractures increases with increasing age, with a six times greater rate in the group age 80 and older compared with the younger age groups (6.34 compared with 1.02 per 10,000 persons per year). The incidence rate of B2.1 fractures decreases with increasing age, with a 2.5 times greater rate in the younger age group than the older age group (2.48 compared with 0.91 per 10,000 persons per year). The incidence rate patterns for fractures of the proximal radius and ulna, separated by AO group and subgroup, previously has not been described in the literature. The overall incidence of observed fracture was similar across all age groups between 18 and 79 years of age, as well as between genders. It is worth noting, however, that the rate of proximal radial and ulnar fractures sharply increases among persons 80 years and older. Although the mechanism of injury was not captured as part of our methodology, this increase may be from falls or poor bone quality among this age group. There were limitations in our study that warrant discussion. These include, but are not limited to, misclassification of cases at initial treatment, errors in the population database and the possibility of selection bias on the part of the authors. First, by looking at fracture injuries, we were able to estimate the presence of misclassification. Although the study was successful at measuring the accuracy of the current coding system, it did not determine at what point any miscoding might have occurred. Miscoding may be the result of an incorrect discharge diagnosis with the correct associated code, a correct discharge diagnosis with an incorrect associated code, or both an incorrect discharge diagnosis and an incorrect associated code. Although the measured percent agreement provides an estimate of the degree of miscoding, the true source of the miscoding could not be determined. The present study was done as part of a larger project, in which the percent agreement between the authors and health region’s database coding system was determined to be 59.03%. Second, as classification of the radiographs and chart notes by the authors is the foundation upon which the estimates of the incidence rates are based, we attempted to identify sources of misclassification that may exist when identifying injuries from a database such as the region’s health records database. However, misclassification may also occur during the authors’ classification of the identified injuries. Although both authors can be considered experts in the field under study, the past clinical experience of the authors affects the classification of the injuries based on the radiographs and chart notes. The relatively poor reliability of the classification systems would suggest that a percentage of the classified cases would be open for discussion and that another set of observers may choose to classify the cases differently.20,21 Ultimately, this would lead to a degree of misclassification of the identified cases by the study authors and would affect the estimated incidence rates. Since a reference standard for the authors was not used, this misclassification could not be accurately measured. Third, the denominator data used for the calculation of injury incidence rates were taken from the 2001 Canadian census, which provides estimates of the overall, age-specific (by decade), and sex-specific population of the city in the present study in 2001. During the period under study (from 2002--2005), there was a change in the population of the city, with an increase in the overall population and an increase in certain age ranges (most likely younger age ranges). Therefore, for the purposes of this study, the use of the 2001 census data would result in an overestimation of the incidence rates, because of the increase in the population of the city during the period under study. This would have resulted in an increase in the value of the denominator used in the incidence rate calculations, and thus a decrease in the calculated incidence rate. However, the presentation of the data with the associated 95% confidence intervals provides the reader with a range of possible values for the estimates of the incidence rates and takes into account the uncertainty associated with the use of the 2001 census data as the denominator in the incidence rate calculations. Lastly, potential sources of selection bias in this study merit consideration. There were limitations in the health records database in regard to capturing all cases. For example, if a fracture was managed by a primary care physician, a private practice orthopaedic surgeon, or under the auspices of the Worker’s Compensation Board, the health region’s database may not capture that injury. This would have resulted in an underestimation of the actual incidence of some injuries. Because records outside of the region’s health records database cannot be sampled because of privacy and logistical reasons, it is impossible to measure the potential magnitude of this selection bias. In conclusion, the information presented in this study highlights the relative magnitude of the clinical burden of proximal radial and ulnar fractures. The incidence rates presented provide a population-based denominator that may be used for future research, allowing for a better estimation of the percentages of positive and negative outcomes as well as complications. REFERENCES 1. 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