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Risk factors for mortality after hip fracture surgery in Japan using the National Database of Health Insurance Claims and Specific Health Checkups of Japan

Risk factors for mortality after hip fracture surgery in Japan using the National Database of... Summary We investigated the risk factors for mortality of hip fracture in the elderly using the National Database of Health Insurance Claims in Japan, and survival was significantly related to sex, age, fracture type, surgical procedure, delayed operative date, comorbidities, blood transfusions, and pulmonary embolism. Purpose Hip fracture is the most common fracture in the elderly and is known to have a high mortality rate. In Japan, to the best of our knowledge, no studies have reported on mortality risk factors for hip fracture using nationwide registry databases. This study aimed to determine the number of occurrences of hip fracture and factors that increase mortality using the National Database of Health Insurance Claims and Specific Health Checkups of Japan. Methods This study included extracted data from patients who were hospitalized and underwent surgical treatment for hip fracture between 2013 and 2021, using a nationwide health insurance claims database in Japan. Patient characteristics, such as sex, age, fracture type, surgical procedure, delayed operative date, comorbidities, blood transfusions, and pulmonary embolism, were tabulated to obtain 1-year and in-hospital mortality rates. Results Both 1-year and in-patient survival were significantly lower in men, older patients, patients who underwent surgery after 3 days of admission, and patients with trochanteric and subtrochanteric fractures, internal fixation, more preoperative comorbidities, blood transfusions, and pulmonary embolism. Conclusions Survival was significantly related to sex, age, fracture type, surgical procedure, delayed operative date, comor - bidities, blood transfusions, and pulmonary embolism. As the number of male patients with hip fracture will increase with the aging of society, medical staff must provide sufficient information before surgery to avoid postoperative mortality. Keywords Hip fracture · National database · Health insurance claim database · Mortality · Risk factors Abbreviations NDB National Database of Health Insurance Claims and * Yusuke Inagaki Specific Health Checkups of Japan yinagaki@naramed-u.ac.jp CCI Charlson comorbidity index * Tatsuya Noda noda@naramed-u.ac.jp Yuki Nishimura Introduction ynishimura@naramed-u.ac.jp 1 Hip fracture is one of the most common fractures in ortho- Department of Orthopaedic Surgery, Nara Medical pedic surgery. Most patients with a hip fracture undergo University, Kashihara, Japan 2 surgery, such as internal fixation, hemiarthroplasty, or total Department of Rehabilitation Medicine, Nara Medical hip replacement. As the world’s population grows and ages, University, Kashihara, Japan 3 the number of hip fractures is expected to increase [1]. Department of Public Health, Health Management Globally, 1.7 million individuals had hip fractures in 1990, and Policy, Nara Medical University, Kashihara, Japan 4 and this number is expected to increase to 6.3 million by Department of Sports Medicine, Nara Medical University, 2050 [2]. Furthermore, hip fracture is associated with high Kashihara, Japan Vol.:(0123456789) 1 3 91 Page 2 of 9 Archives of Osteoporosis (2023) 18:91 mortality and morbidity in the elderly population [3]. The the World Medical Association Code of Ethics on Experi- age- and sex-adjusted 1-year mortality rate for hip fracture ments on Human Subjects (Declaration of Helsinki) and is estimated to be approximately 20–30%, and the 30-day was approved by the Ethics Committee of Nara Medical mortality rate for hip fracture is estimated to be 5–10% University (No. 2831). As the data were anonymized, [4]. Various studies have reported on the risk factors for the requirement of obtaining informed consent from hip fracture, including aging, male sex, and complications individual patients was waived. The database comprised [5–7]. There are several studies that have used the national information on procedure codes, procedure application registry database or a claim database to determine mortality dates, admission dates, International Classification of risk factors for hip fracture [8, 9]; nevertheless, there are no Diseases and Related Health Problems, Tenth Edition observational studies with fewer omissions based on national (ICD-10) codes, ICD-10 code documentation dates, all-source data of 100 million people. And in Japan, local and age category codes. Hip fracture was selected from reports are predominant, and no such studies using nation- ICD-10 codes for the following three conditions: cervical wide registry databases have been reported. fracture (ICD-10, S7200), trochanteric fracture (ICD-10, In Japan, the National Database of Health Insurance S7210), and subtrochanteric fracture (ICD-10, S7220). Claims and Specific Health Checkups of Japan (NDB) was Patients younger than 65 years and those with open frac- established in 2009. Moreover, Japan has a national health tures (ICD-10, S7201, S7211, and S7221) were excluded insurance system, and the NDB has the advantage of cov- from the extracted data. All analyses were performed ering most of the population’s data. It is an all-insurance using anonymized data by the NDB. medical survey that stores almost all the data on medical treatment received by 120 million Japanese citizens. Pre- vious studies analyzing the NDB showed diverse sample Covariates sizes. This study successfully analyzed a full-size NDB covering almost all Japanese medical examination data, The number of patients operated on for hip fracture from and also incorporated techniques for individual track- the NDB was categorized by sex (man and woman), age ing beyond transfers and relocations [10]. Therefore, this group (5-year age groups starting at age 65–69 and ending study achieved the largest sample size of hip fracture at age 95 or older), fracture type (cervical, trochanteric, patients with smallest selection bias compared to previ- and subtrochanteric), procedure (internal fixation, hemi- ous studies. Japan has the highest aging rate worldwide, arthroplasty, and total hip replacement), date of surgery with 30% of the population expected to be aged 65 or after admission (day 0, 1, 2, 3 or later), and the Charlson older by 2025 [11]. Because Japan is leading the world comorbidity index (CCI) [12] at admission. The CCI was in terms of having an aging society, other countries with identified from ICD-10 codes based on previous literature aging societies would benefit from comprehensive data [13]. Furthermore, patients who had a blood transfusion collection and research. or a pulmonary embolism were also categorized. This is the first study to investigate hip fracture trends and mortality risk factors by analyzing almost all Japanese patients with hip fracture using the NDB, which is one of Statistical analysis the largest claims databases in the world. We used death identification logic in our analysis of the NDB, as described previously [14]. The Kaplan–Meier Materials and methods life table method was used to calculate the 1-year sur- vival rate per month after hip fracture between April Data sources 2013 and March 2021. Graphs were created to compare crude survival rates at 1 year from admission by sex, age We extracted data from the NDB of the Department of group, fracture type, procedure type, date of surgery, Health of the Ministry of Health, Labour and Welfare, CCI score (0, 1, 2, 3, 4, 5, or ≥6), blood transfusion (yes Japan. Patient tracking/aggregation was performed using or no), and pulmonary embolism (yes or no). Log-rank our patient tracking technology [10]. From the NDB, tests were performed to compare the groups, and fac- hospitalized patients who underwent internal fixation, tors that increase mortality were analyzed by estimating hemiarthroplasty, or total hip replacement for a first the adjusted hazard ratio (aHR) and its 95% confidence hip fracture during the 8-year period from April 2013 interval using Cox proportional hazards regression. In to March 2021 were selected. The at-risk period was addition to 1-year mortality, the number of deaths and defined as the period up to the month of the last medical mortality rates during hospitalization were analyzed. practice. This study was conducted in accordance with All analyses were performed using IBM SPSS v.28.0 1 3 Archives of Osteoporosis (2023) 18:91 Page 3 of 9 91 for Windows (IBM Institute, Inc., Cary, NC, USA), and Mortality and related risk factors a significance level of 5% was adopted. Figure 2 compares 1-year survival rates for hip fractures by sex, age, fracture type, procedure type, date of surgery Results since admission, CCI, blood transfusion, and pulmonary embolism. Survival rates were significantly lower in men, Patients the oldest group (≥95 years), the trochanteric and sub- trochanteric group, the internal fixation group, the late The overall number of hip fractures was 1,192,884 (men, operation group, the highest CCI group (CCI ≥6), the 249,747; women, 943,137), excluding 61,038 patients group with blood transfusions, and the group with pul- under 65 years and 239 patients with open fractures monary embolism. Table 3 shows the results of the Cox (Fig. 1). As shown in Table 1, the age range between 85 regression analysis. Independent factors that significantly and 90 years was the most common for both men and increased the hazard ratio for mortality were as follows: women, accounting for 25.2% of men and 28.1% of women. male sex (aHR, 2.29; 95% CI, 2.26–2.32), older age (aHR, Cervical fractures were the most common type of fracture, 5.93; 95% CI, 5.67–6.19 for age ≥95 vs. age 65–69), frac- slightly more common than trochanteric. Internal fixation ture type (aHR, 1.24; 95% CI, 1.23–1.26 for trochanteric was the most common among operation types, accounting fracture vs. cervical fracture), internal fixation procedure for 60% of male patients and 63.5% of female patients. (aHR, 0.79; 95% CI, 0.78–0.79 for hemiarthroplasty vs. More than half of the patients (men, 62.7%; women, internal fixation), delayed operative date (aHR, 1.03; 59.9%) underwent surgery on day 3 or after. A CCI of 2 95% CI, 1.00–1.05 for day ≥3 vs. day 0), high CCI (aHR, for men and 1 for women was most common. The percent- 4.41; 95% CI, 4.31–4.52 for CCI ≥6 vs CCI =0), blood age of patients with CCI 6 or higher was 15.7% for men transfusion (aHR, 1.98; 95% CI, 1.96–2.00), and pulmo- compared to 6.9% for women, with a trend toward more nary embolism (aHR, 1.61; 95% CI, 1.52–1.71). Mortal- comorbidities in men. ity during hospitalization was also significantly higher in men, the older group, the trochanteric and subtrochan- Complications teric group, the internal fixation group, the late operation group, the high CCI group, the group with blood transfu- As shown in Table  2, 89,814 men and 395,926 women sions, and the group with pulmonary embolism. Moreo- received blood transfusions during hospitalization, with ver, the mortality rate was significantly higher, especially percentages of 36.0% and 42.0%, respectively. A total of in men with age ≥95 years (7.9%), subtrochanteric frac- 1268 men and 6167 women were affected by pulmonary tures (5.2%), CCI ≥6 (6.6%), blood transfusions (6.3%), embolism, with percentages of 0.5% and 0.7%, respectively. and pulmonary embolism (12.7%) (Table 4). Fig. 1 Case selection, identifi- cation, and exclusions 1 3 91 Page 4 of 9 Archives of Osteoporosis (2023) 18:91 Table 1 Patient characteristics No. (%) Characteristic Total (N=1,192,884) Men (n=249,747) Women (n=943,137) Age, years Mean (SD) 65–69 51,737 (4.3) 17,122 (6.9) 34,615 (3.7) 70–74 83,782 (7.0) 25,500 (10.2) 58,282 (6.2) 75–79 149,808 (12.6) 40,614 (16.3) 109,194 (11.6) 80–84 260,451 (21.8) 59,950 (24.0) 200,501 (21.3) 85–89 328,373 (27.5) 63,005 (25.2) 265,368 (28.1) 90–94 232,733 (19.5) 34,054 (13.6) 198,679 (21.1) ≥95 86,000 (7.2) 9502 (3.8) 76,498 (8.1) Fracture type Cervical 621,640 (51.1) 137,761 (54.2) 483,879 (50.3) Trochanteric 569,157 (46.8) 111,951 (44.0) 457,206 (47.5) Subtrochanteric 24,875 (2.0) 4397 (1.7) 20,478 (2.2) Operation type Internal fixation 750,426 (62.9) 150,120 (60.1) 600,306 (63.6) Hemiarthroplasty 428,921 (35.9) 96,924 (38.8) 331,997 (35.2) Total hip replacement 14,549 (1.2) 2918 (1.1) 11,631 (1.2) Operation day Day 0 81,545 (6.8) 16,001 (6.4) 65,544 (6.9) Day 1 203,908 (17.1) 40,464 (16.2) 163,444 (17.3) Day 2 185,187 (15.5) 36,555 (14.6) 148,632 (15.8) Day ≥3 722,244 (60.5) 156,727 (62.7) 565,517 (60.0) Charlson comorbidity index score 0 191,361 (16.0) 31,249 (12.5) 160,112 (17.0) 1 265,640 (22.3) 41,858 (16.8) 223,782 (23.7) 2 248,177 (20.8) 44,661 (17.9) 203,516 (21.6) 3 185,957 (15.6) 39,617 (15.9) 146,340 (15.5) 4 122,551 (10.3) 31,007 (12.4) 91,544 (9.7) 5 74,231 (6.2) 21,905 (8.8) 52,326 (5.5) ≥6 104,967 (8.8) 39,450 (15.8) 65,517 (6.9) Table 2 Patient complications No. (%) Complication Total (N=1,192,884) Men (n=249,747) Women (n=943,137) Transfusion Yes 485,740 (40.7) 89,814 (36.0) 395,926 (42.0) None 707,144 (59.3) 159,933 (64.0) 547,211 (58.0) Pulmonary embolism Yes 7435 (0.6) 1268 (0.5) 6167 (0.7) None 1,185,449 (99.4) 248,479 (99.5) 936,970 (99.3) with blood transfusions, and the group with pulmonary Discussion embolism. Our study included patients hospitalized and operated on This study investigated risk factors for mortality after hip for hip fractures included in the NDB data from 2013 to fracture surgery. Survival rates were significantly lower 2021. Data on 1,192,884 patients were extracted, which is in men, the oldest group (≥95 years), the trochanteric and one of the largest number of cases compared to previous subtrochanteric group, the internal fixation group, the late studies. Ogawa et al. used the Japanese Diagnosis Procedure operation group, the highest CCI group (CCI ≥6), the group 1 3 Archives of Osteoporosis (2023) 18:91 Page 5 of 9 91 Fig. 2 Survival for 1 year after hip fracture in each group 1 3 91 Page 6 of 9 Archives of Osteoporosis (2023) 18:91 Fig. 2 (continued) 1 3 Archives of Osteoporosis (2023) 18:91 Page 7 of 9 91 Table 3 Hazard ratios for 1-year mortality after hip fracture based on Table 4 Number of deaths and mortality rates during hospitalization multivariable Cox regression Characteristic No. (%) Characteristic Hazard ratio (95%CI) Total Men Women Male sex 2.29 (2.26–2.32) All 20,946 (2.0) 8236 (3.8) 12,710 (1.5) Age, years Age, years 65–69 1 [Reference] Mean (SD) 70–74 1.33 (1.26–1.39) 65–69 429 (0.9) 202 (1.3) 227 (0.7) 75–79 1.68 (1.61–1.76) 70–74 828 (1.1) 406 (1.8) 422 (0.8) 80–84 2.21 (2.12–2.31) 75–79 1839 (1.4) 928 (2.6) 911 (0.9) 85–89 2.99 (2.87–3.12) 80–84 3734 (1.6) 1756 (3.3) 1978 (1.1) 90–94 4.12 (3.95–4.29) 85–89 6043 (2.1) 2579 (4.7) 3464 (1.5) ≥95 5.93 (5.67–6.19) 90–94 5385 (2.7) 1729 (6.0) 3656 (2.1) Fracture type ≥95 2688 (3.7) 636 (7.9) 2052 (3.1) Cervical 1 [Reference] Fracture type Trochanteric 1.24 (1.23–1.26) Cervical 10,048 (1.9) 4237 (3.6) 5811 (1.4) Subtrochanteric 1.26 (1.21–1.31) Trochanteric 10,786 (2.2) 3972 (4.1) 6814 (1.7) Operation type Subtrochanteric 625 (2.9) 199 (5.2) 426 (2.4) Internal fixation 1 [Reference] Operation type Hemiarthroplasty 0.79 (0.78–0.79) Internal fixation 14,279 (2.2) 5331 (4.1) 8948 (1.7) Total hip replacement 0.32 (0.29–0.35) Hemiarthroplasty 6603 (1.8) 2875 (3.4) 3728 (1.3) Operation day Total hip replacement 86 (0.7) 40 (1.7) 46 (0.5) Day 0 1 [Reference] Operation day Day 1 0.93 (0.91–0.96) Day 0 1128 (1.6) 417 (3.1) 711 (1.3) Day 2 0.92 (0.90–0.94) Day 1 2802 (1.6) 1059 (3.1) 1743 (1.3) Day ≥3 1.03 (1.00–1.05) Day 2 2618 (1.6) 1024 (3.3) 1594 (1.2) Charlson comorbidity index score Day ≥3 14,398 (2.2) 5736 (4.2) 8662 (1.7) 0 1 [Reference] Charlson comorbidity index score 1 1.57 (1.53–1.61) 0 1241 (0.7) 418 (1.5) 823 (0.6) 2 2.07 (2.02–2.12) 1 2716 (1.2) 849 (2.3) 1867 (1.0) 3 2.46 (2.40–2.53) 2 3675 (1.7) 1293 (3.3) 2382 (1.3) 4 2.85 (2.77–2.92) 3 3537 (2.2) 1286 (3.8) 2251 (1.8) 5 3.17 (3.08–3.26) 4 2983 (2.8) 1215 (4.5) 1768 (2.2) ≥6 4.41 (4.31–4.52) 5 2096 (3.2) 930 (4.9) 1166 (2.5) Transfusion 1.98 (1.96–2.00) ≥6 4698 (5.1) 2245 (6.6) 2453 (4.3) Pulmonary embolism 1.61 (1.52–1.71) Transfusion Yes 13,069 (3.1) 4861 (6.3) 8208 (2.4) None 7877 (1.3) 3375 (2.4) 4502 (0.9) Pulmonary embolism Combination inpatient database to report seasonal mortal- Yes 494 (7.7) 135 (12.7) 359 (6.7) ity of hip fracture in 425,856 patients [15]. In this study, None 20,452 (2.0) 8101 (3.8) 12,351 (1.5) the 1-year mortality rate for hip fracture was 20.6% in men and 9.5% in women. This compares to previous reports of 21% and 23.9% for hip fracture patients with similar 1-year mortality rates in men [16, 17]. The lower 1-year mortality subtrochanteric fractures had similar mortality rates in both rate for women in this study compared to those observed in sexes, with cervical fractures having a lower mortality rate. previous studies may have been due to the longer life expec- Similarly, compared to cervical fractures, trochanteric and tancy in Japan, as it has more advanced medical technology. subtrochanteric fractures are associated with older age and The 1-year and in-hospital mortality rates tended to increase higher CCI scores [18]. Fracture patterns range from simple with age, with 37.8% of men and 19% of women over 95 to unstable, and patients with unstable fractures may not years of age dying, and the hazard ratio was 5.93, which was be able to load immediately postoperatively, and the longer higher than that in the 65–69 age group. Studies on hip frac- time between surgery and transfer increases complications ture mortality risk have also revealed that age is significantly and mortality [19]. These factors may have contributed to related to mortality [7]. For fracture type, trochanteric and the lower mortality rate in patients with cervical fractures. In 1 3 91 Page 8 of 9 Archives of Osteoporosis (2023) 18:91 addition, because trochanteric and subtrochanteric fractures that transfusion itself may be a risk factor for death. As a are generally treated with internal fixation, the mortality rate result, it is advised to be cautious about intraoperative bleed- of internal fixation was higher than that of hemiarthroplasty ing and to limit postoperative blood transfusions to only or total hip replacement. In a randomized clinical trial com- when absolutely necessary. paring hemiarthroplasty and total hip replacement in patients Although past studies have mainly examined risk factors with hip fracture, patients who underwent total hip replace- for pulmonary embolism because of its low incidence [28, ment had a 58% reduction in 12-month mortality risk [20]. 29], this is the r fi st study to examine the 1-year and in-hospital The patients were matched for age, sex, and pre-fracture mortality rates of hip fracture in cases of pulmonary embo- activity, suggesting that the total hip replacement procedure lism. In particular, we should be concerned about the pre- itself may reduce postoperative mortality. In light of this, vention of deep vein thrombosis in the perioperative period total hip replacement is commonly performed in Japan not since pulmonary embolism increases the mortality rate during only in patients with hip osteoarthritis, but also in patients hospitalization by about four times in both men and women. with numerous daily life activities and relatively young Our study found that male patients from various back- patients with hip fracture. grounds had higher 1-year and in-hospital mortality rates. In terms of surgical delay, if the surgery is performed Although osteoporosis usually affects women, the results after 48 hours of hospitalization, the mortality rate at 3 and suggest that male patients with osteoporosis may be more 12 months after surgery for hip fracture in elderly patients fragile. To our knowledge, no previous study has evaluated increases [21]. Conversely, other studies have shown no effect risk factors for long-term mortality from hip fracture in the on mortality within 30 days [22]. However, there is still no entire Japanese population. Furthermore, this study has very agreement on the relationship between early hip fracture sur- little missing data, so our sample is considered representa- gery and postoperative mortality [23]. In our study, the 1-year tive of the population in this region. mortality rate was slightly higher in the group of patients There are several limitations to this study. First, it is a ret- who underwent surgery after the third day of hospitaliza- rospective study. Second, it was based on an insurance data- tion. This may be due to the fact that the date of injury did base and does not include patients who were not treated by not always coincide with the date of admission, such as in insurance, such as those who had medical assistance for wel- cases of fracture during hospitalization. Although there was fare, compulsory automobile liability insurance, or publicly little difference in 1-year mortality in this study. Shen et al. funded medical care. Finally, several other factors that cannot reported that surgical delay increases postoperative compli- be extracted from the database may also be associated with cations such as pneumonia and myocardial infarction [24]; higher mortality rates, such as secondary osteoporosis caused thus, it is presumably better to perform surgery as early as by steroids, other drugs, or endocrine disorders. The reason for possible. In this study, approximately 60% of both male and this is that this database consists of Japanese claim data, and female patients underwent surgery after the third day of hos- items such as blood test results cannot be determined. Despite pitalization. In Japan, early surgery after a hip fracture injury these limitations, it is assumed that few people are excluded is recommended, but this has not yet been achieved. from the data because most Japanese citizens have medical With regard to CCI, mortality increased progressively insurance, and most patients with hip fractures receive treat- with increasing CCI scores in both men and women, with ment through medical insurance. Therefore, further studies are a particularly high 1-year mortality rate of 30.9% and an needed to investigate other mortality risk factors. in-hospital mortality rate of 6.6% in the group of men with In conclusion, male sex, older age, fracture type (trochan- CCI scores of 6 or higher. Therefore, a high CCI score was teric and subtrochanteric fracture), internal fixation proce- identified as a potential risk factor for 1-year mortality in this dure, delayed operative date, the number of comorbidities, patient population. Previous reports have shown that higher blood transfusion, and pulmonary embolism were signifi- CCI increases both short- and long-term mortality [25], and cantly associated with risk factors for 1-year mortality in this study describes specific mortality rates for each CCI. hip fracture. In addition, men had higher mortality rates than Regarding blood transfusions and pulmonary embolism, women in all categories. In the future, the number of male both significantly increased 1-year and in-hospital mortal- patients with hip fractures will increase with the aging of ity. While some studies reported that transfusions increase society, and medical staff must provide sufficient informa- 1-year mortality by 2.79-fold [26], other studies reported tion before surgery to avoid postoperative mortality. that the difference was not significant when patients were Supplementary Information The online version contains supplemen- matched for background [27]. These results suggest that tary material available at https://doi. or g/10. 1007/ s11657- 023- 01293-z . patients who receive blood transfusions are also likely to have poor preoperative conditions, such as anemia. Acknowledgements We would like to thank Editage (www.editage. com) for English language editing. We greatly appreciate Mitsubishi In this study, the 1-year mortality hazard ratio for trans- Research Institute, Inc. for analytical assistance. fused patients after multivariate analysis was 1.98, suggesting 1 3 Archives of Osteoporosis (2023) 18:91 Page 9 of 9 91 Funding This work was supported by the Health Labour Sciences 12. Charlson ME, Pompei P, Ales KL, MacKenzie CR (1987) A new Research Grant (Grant Number: 20HB1001) and JSPS KAKENHI method of classifying prognostic comorbidity in longitudinal stud- (Grant Numbers: JP20H00623, JP18H04126). ies: development and validation. J Chronic Dis 40:373–383 13. Zhang Z, Yang H, Luo M (2021) Association between Charlson comorbidity index and community-acquired pressure injury in Declarations older acute inpatients in a Chinese tertiary hospital. Clin Interv Aging 16:1987–1995 Ethical approval For this type of study, formal consent is not required. 14. Kubo S, Noda T, Nishioka Y, Myojin T, Nakanishi Y, Furi- hata S, Higashino T, Imamura T (2020) Mortality tracking Conflicts of interest None. using the National Database of Health Insurance Claims and Specific Health Checkups of Japan (NDB). Jpn J Med Inform Open Access This article is licensed under a Creative Commons Attri- 40:319–335 bution 4.0 International License, which permits use, sharing, adapta- 15. Ogawa T, Yoshii T, Higuchi M, Morishita S, Fushimi K, Fuji- tion, distribution and reproduction in any medium or format, as long wara T, Okawa A (2021) Seasonality of mortality and in-hos- as you give appropriate credit to the original author(s) and the source, pital complications in hip fracture surgery: retrospective cohort provide a link to the Creative Commons licence, and indicate if changes research using a nationwide inpatient database. Geriatr Gerontol were made. The images or other third party material in this article are Int 21:398–403 included in the article's Creative Commons licence, unless indicated 16. Ariza-Vega P, Kristensen MT, Martin-Martin L, Jimenez-Moleon otherwise in a credit line to the material. If material is not included in JJ (2015) Predictors of long-term mortality in older people with the article's Creative Commons licence and your intended use is not hip fracture. 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Risk factors for mortality after hip fracture surgery in Japan using the National Database of Health Insurance Claims and Specific Health Checkups of Japan

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Abstract

Summary We investigated the risk factors for mortality of hip fracture in the elderly using the National Database of Health Insurance Claims in Japan, and survival was significantly related to sex, age, fracture type, surgical procedure, delayed operative date, comorbidities, blood transfusions, and pulmonary embolism. Purpose Hip fracture is the most common fracture in the elderly and is known to have a high mortality rate. In Japan, to the best of our knowledge, no studies have reported on mortality risk factors for hip fracture using nationwide registry databases. This study aimed to determine the number of occurrences of hip fracture and factors that increase mortality using the National Database of Health Insurance Claims and Specific Health Checkups of Japan. Methods This study included extracted data from patients who were hospitalized and underwent surgical treatment for hip fracture between 2013 and 2021, using a nationwide health insurance claims database in Japan. Patient characteristics, such as sex, age, fracture type, surgical procedure, delayed operative date, comorbidities, blood transfusions, and pulmonary embolism, were tabulated to obtain 1-year and in-hospital mortality rates. Results Both 1-year and in-patient survival were significantly lower in men, older patients, patients who underwent surgery after 3 days of admission, and patients with trochanteric and subtrochanteric fractures, internal fixation, more preoperative comorbidities, blood transfusions, and pulmonary embolism. Conclusions Survival was significantly related to sex, age, fracture type, surgical procedure, delayed operative date, comor - bidities, blood transfusions, and pulmonary embolism. As the number of male patients with hip fracture will increase with the aging of society, medical staff must provide sufficient information before surgery to avoid postoperative mortality. Keywords Hip fracture · National database · Health insurance claim database · Mortality · Risk factors Abbreviations NDB National Database of Health Insurance Claims and * Yusuke Inagaki Specific Health Checkups of Japan yinagaki@naramed-u.ac.jp CCI Charlson comorbidity index * Tatsuya Noda noda@naramed-u.ac.jp Yuki Nishimura Introduction ynishimura@naramed-u.ac.jp 1 Hip fracture is one of the most common fractures in ortho- Department of Orthopaedic Surgery, Nara Medical pedic surgery. Most patients with a hip fracture undergo University, Kashihara, Japan 2 surgery, such as internal fixation, hemiarthroplasty, or total Department of Rehabilitation Medicine, Nara Medical hip replacement. As the world’s population grows and ages, University, Kashihara, Japan 3 the number of hip fractures is expected to increase [1]. Department of Public Health, Health Management Globally, 1.7 million individuals had hip fractures in 1990, and Policy, Nara Medical University, Kashihara, Japan 4 and this number is expected to increase to 6.3 million by Department of Sports Medicine, Nara Medical University, 2050 [2]. Furthermore, hip fracture is associated with high Kashihara, Japan Vol.:(0123456789) 1 3 91 Page 2 of 9 Archives of Osteoporosis (2023) 18:91 mortality and morbidity in the elderly population [3]. The the World Medical Association Code of Ethics on Experi- age- and sex-adjusted 1-year mortality rate for hip fracture ments on Human Subjects (Declaration of Helsinki) and is estimated to be approximately 20–30%, and the 30-day was approved by the Ethics Committee of Nara Medical mortality rate for hip fracture is estimated to be 5–10% University (No. 2831). As the data were anonymized, [4]. Various studies have reported on the risk factors for the requirement of obtaining informed consent from hip fracture, including aging, male sex, and complications individual patients was waived. The database comprised [5–7]. There are several studies that have used the national information on procedure codes, procedure application registry database or a claim database to determine mortality dates, admission dates, International Classification of risk factors for hip fracture [8, 9]; nevertheless, there are no Diseases and Related Health Problems, Tenth Edition observational studies with fewer omissions based on national (ICD-10) codes, ICD-10 code documentation dates, all-source data of 100 million people. And in Japan, local and age category codes. Hip fracture was selected from reports are predominant, and no such studies using nation- ICD-10 codes for the following three conditions: cervical wide registry databases have been reported. fracture (ICD-10, S7200), trochanteric fracture (ICD-10, In Japan, the National Database of Health Insurance S7210), and subtrochanteric fracture (ICD-10, S7220). Claims and Specific Health Checkups of Japan (NDB) was Patients younger than 65 years and those with open frac- established in 2009. Moreover, Japan has a national health tures (ICD-10, S7201, S7211, and S7221) were excluded insurance system, and the NDB has the advantage of cov- from the extracted data. All analyses were performed ering most of the population’s data. It is an all-insurance using anonymized data by the NDB. medical survey that stores almost all the data on medical treatment received by 120 million Japanese citizens. Pre- vious studies analyzing the NDB showed diverse sample Covariates sizes. This study successfully analyzed a full-size NDB covering almost all Japanese medical examination data, The number of patients operated on for hip fracture from and also incorporated techniques for individual track- the NDB was categorized by sex (man and woman), age ing beyond transfers and relocations [10]. Therefore, this group (5-year age groups starting at age 65–69 and ending study achieved the largest sample size of hip fracture at age 95 or older), fracture type (cervical, trochanteric, patients with smallest selection bias compared to previ- and subtrochanteric), procedure (internal fixation, hemi- ous studies. Japan has the highest aging rate worldwide, arthroplasty, and total hip replacement), date of surgery with 30% of the population expected to be aged 65 or after admission (day 0, 1, 2, 3 or later), and the Charlson older by 2025 [11]. Because Japan is leading the world comorbidity index (CCI) [12] at admission. The CCI was in terms of having an aging society, other countries with identified from ICD-10 codes based on previous literature aging societies would benefit from comprehensive data [13]. Furthermore, patients who had a blood transfusion collection and research. or a pulmonary embolism were also categorized. This is the first study to investigate hip fracture trends and mortality risk factors by analyzing almost all Japanese patients with hip fracture using the NDB, which is one of Statistical analysis the largest claims databases in the world. We used death identification logic in our analysis of the NDB, as described previously [14]. The Kaplan–Meier Materials and methods life table method was used to calculate the 1-year sur- vival rate per month after hip fracture between April Data sources 2013 and March 2021. Graphs were created to compare crude survival rates at 1 year from admission by sex, age We extracted data from the NDB of the Department of group, fracture type, procedure type, date of surgery, Health of the Ministry of Health, Labour and Welfare, CCI score (0, 1, 2, 3, 4, 5, or ≥6), blood transfusion (yes Japan. Patient tracking/aggregation was performed using or no), and pulmonary embolism (yes or no). Log-rank our patient tracking technology [10]. From the NDB, tests were performed to compare the groups, and fac- hospitalized patients who underwent internal fixation, tors that increase mortality were analyzed by estimating hemiarthroplasty, or total hip replacement for a first the adjusted hazard ratio (aHR) and its 95% confidence hip fracture during the 8-year period from April 2013 interval using Cox proportional hazards regression. In to March 2021 were selected. The at-risk period was addition to 1-year mortality, the number of deaths and defined as the period up to the month of the last medical mortality rates during hospitalization were analyzed. practice. This study was conducted in accordance with All analyses were performed using IBM SPSS v.28.0 1 3 Archives of Osteoporosis (2023) 18:91 Page 3 of 9 91 for Windows (IBM Institute, Inc., Cary, NC, USA), and Mortality and related risk factors a significance level of 5% was adopted. Figure 2 compares 1-year survival rates for hip fractures by sex, age, fracture type, procedure type, date of surgery Results since admission, CCI, blood transfusion, and pulmonary embolism. Survival rates were significantly lower in men, Patients the oldest group (≥95 years), the trochanteric and sub- trochanteric group, the internal fixation group, the late The overall number of hip fractures was 1,192,884 (men, operation group, the highest CCI group (CCI ≥6), the 249,747; women, 943,137), excluding 61,038 patients group with blood transfusions, and the group with pul- under 65 years and 239 patients with open fractures monary embolism. Table 3 shows the results of the Cox (Fig. 1). As shown in Table 1, the age range between 85 regression analysis. Independent factors that significantly and 90 years was the most common for both men and increased the hazard ratio for mortality were as follows: women, accounting for 25.2% of men and 28.1% of women. male sex (aHR, 2.29; 95% CI, 2.26–2.32), older age (aHR, Cervical fractures were the most common type of fracture, 5.93; 95% CI, 5.67–6.19 for age ≥95 vs. age 65–69), frac- slightly more common than trochanteric. Internal fixation ture type (aHR, 1.24; 95% CI, 1.23–1.26 for trochanteric was the most common among operation types, accounting fracture vs. cervical fracture), internal fixation procedure for 60% of male patients and 63.5% of female patients. (aHR, 0.79; 95% CI, 0.78–0.79 for hemiarthroplasty vs. More than half of the patients (men, 62.7%; women, internal fixation), delayed operative date (aHR, 1.03; 59.9%) underwent surgery on day 3 or after. A CCI of 2 95% CI, 1.00–1.05 for day ≥3 vs. day 0), high CCI (aHR, for men and 1 for women was most common. The percent- 4.41; 95% CI, 4.31–4.52 for CCI ≥6 vs CCI =0), blood age of patients with CCI 6 or higher was 15.7% for men transfusion (aHR, 1.98; 95% CI, 1.96–2.00), and pulmo- compared to 6.9% for women, with a trend toward more nary embolism (aHR, 1.61; 95% CI, 1.52–1.71). Mortal- comorbidities in men. ity during hospitalization was also significantly higher in men, the older group, the trochanteric and subtrochan- Complications teric group, the internal fixation group, the late operation group, the high CCI group, the group with blood transfu- As shown in Table  2, 89,814 men and 395,926 women sions, and the group with pulmonary embolism. Moreo- received blood transfusions during hospitalization, with ver, the mortality rate was significantly higher, especially percentages of 36.0% and 42.0%, respectively. A total of in men with age ≥95 years (7.9%), subtrochanteric frac- 1268 men and 6167 women were affected by pulmonary tures (5.2%), CCI ≥6 (6.6%), blood transfusions (6.3%), embolism, with percentages of 0.5% and 0.7%, respectively. and pulmonary embolism (12.7%) (Table 4). Fig. 1 Case selection, identifi- cation, and exclusions 1 3 91 Page 4 of 9 Archives of Osteoporosis (2023) 18:91 Table 1 Patient characteristics No. (%) Characteristic Total (N=1,192,884) Men (n=249,747) Women (n=943,137) Age, years Mean (SD) 65–69 51,737 (4.3) 17,122 (6.9) 34,615 (3.7) 70–74 83,782 (7.0) 25,500 (10.2) 58,282 (6.2) 75–79 149,808 (12.6) 40,614 (16.3) 109,194 (11.6) 80–84 260,451 (21.8) 59,950 (24.0) 200,501 (21.3) 85–89 328,373 (27.5) 63,005 (25.2) 265,368 (28.1) 90–94 232,733 (19.5) 34,054 (13.6) 198,679 (21.1) ≥95 86,000 (7.2) 9502 (3.8) 76,498 (8.1) Fracture type Cervical 621,640 (51.1) 137,761 (54.2) 483,879 (50.3) Trochanteric 569,157 (46.8) 111,951 (44.0) 457,206 (47.5) Subtrochanteric 24,875 (2.0) 4397 (1.7) 20,478 (2.2) Operation type Internal fixation 750,426 (62.9) 150,120 (60.1) 600,306 (63.6) Hemiarthroplasty 428,921 (35.9) 96,924 (38.8) 331,997 (35.2) Total hip replacement 14,549 (1.2) 2918 (1.1) 11,631 (1.2) Operation day Day 0 81,545 (6.8) 16,001 (6.4) 65,544 (6.9) Day 1 203,908 (17.1) 40,464 (16.2) 163,444 (17.3) Day 2 185,187 (15.5) 36,555 (14.6) 148,632 (15.8) Day ≥3 722,244 (60.5) 156,727 (62.7) 565,517 (60.0) Charlson comorbidity index score 0 191,361 (16.0) 31,249 (12.5) 160,112 (17.0) 1 265,640 (22.3) 41,858 (16.8) 223,782 (23.7) 2 248,177 (20.8) 44,661 (17.9) 203,516 (21.6) 3 185,957 (15.6) 39,617 (15.9) 146,340 (15.5) 4 122,551 (10.3) 31,007 (12.4) 91,544 (9.7) 5 74,231 (6.2) 21,905 (8.8) 52,326 (5.5) ≥6 104,967 (8.8) 39,450 (15.8) 65,517 (6.9) Table 2 Patient complications No. (%) Complication Total (N=1,192,884) Men (n=249,747) Women (n=943,137) Transfusion Yes 485,740 (40.7) 89,814 (36.0) 395,926 (42.0) None 707,144 (59.3) 159,933 (64.0) 547,211 (58.0) Pulmonary embolism Yes 7435 (0.6) 1268 (0.5) 6167 (0.7) None 1,185,449 (99.4) 248,479 (99.5) 936,970 (99.3) with blood transfusions, and the group with pulmonary Discussion embolism. Our study included patients hospitalized and operated on This study investigated risk factors for mortality after hip for hip fractures included in the NDB data from 2013 to fracture surgery. Survival rates were significantly lower 2021. Data on 1,192,884 patients were extracted, which is in men, the oldest group (≥95 years), the trochanteric and one of the largest number of cases compared to previous subtrochanteric group, the internal fixation group, the late studies. Ogawa et al. used the Japanese Diagnosis Procedure operation group, the highest CCI group (CCI ≥6), the group 1 3 Archives of Osteoporosis (2023) 18:91 Page 5 of 9 91 Fig. 2 Survival for 1 year after hip fracture in each group 1 3 91 Page 6 of 9 Archives of Osteoporosis (2023) 18:91 Fig. 2 (continued) 1 3 Archives of Osteoporosis (2023) 18:91 Page 7 of 9 91 Table 3 Hazard ratios for 1-year mortality after hip fracture based on Table 4 Number of deaths and mortality rates during hospitalization multivariable Cox regression Characteristic No. (%) Characteristic Hazard ratio (95%CI) Total Men Women Male sex 2.29 (2.26–2.32) All 20,946 (2.0) 8236 (3.8) 12,710 (1.5) Age, years Age, years 65–69 1 [Reference] Mean (SD) 70–74 1.33 (1.26–1.39) 65–69 429 (0.9) 202 (1.3) 227 (0.7) 75–79 1.68 (1.61–1.76) 70–74 828 (1.1) 406 (1.8) 422 (0.8) 80–84 2.21 (2.12–2.31) 75–79 1839 (1.4) 928 (2.6) 911 (0.9) 85–89 2.99 (2.87–3.12) 80–84 3734 (1.6) 1756 (3.3) 1978 (1.1) 90–94 4.12 (3.95–4.29) 85–89 6043 (2.1) 2579 (4.7) 3464 (1.5) ≥95 5.93 (5.67–6.19) 90–94 5385 (2.7) 1729 (6.0) 3656 (2.1) Fracture type ≥95 2688 (3.7) 636 (7.9) 2052 (3.1) Cervical 1 [Reference] Fracture type Trochanteric 1.24 (1.23–1.26) Cervical 10,048 (1.9) 4237 (3.6) 5811 (1.4) Subtrochanteric 1.26 (1.21–1.31) Trochanteric 10,786 (2.2) 3972 (4.1) 6814 (1.7) Operation type Subtrochanteric 625 (2.9) 199 (5.2) 426 (2.4) Internal fixation 1 [Reference] Operation type Hemiarthroplasty 0.79 (0.78–0.79) Internal fixation 14,279 (2.2) 5331 (4.1) 8948 (1.7) Total hip replacement 0.32 (0.29–0.35) Hemiarthroplasty 6603 (1.8) 2875 (3.4) 3728 (1.3) Operation day Total hip replacement 86 (0.7) 40 (1.7) 46 (0.5) Day 0 1 [Reference] Operation day Day 1 0.93 (0.91–0.96) Day 0 1128 (1.6) 417 (3.1) 711 (1.3) Day 2 0.92 (0.90–0.94) Day 1 2802 (1.6) 1059 (3.1) 1743 (1.3) Day ≥3 1.03 (1.00–1.05) Day 2 2618 (1.6) 1024 (3.3) 1594 (1.2) Charlson comorbidity index score Day ≥3 14,398 (2.2) 5736 (4.2) 8662 (1.7) 0 1 [Reference] Charlson comorbidity index score 1 1.57 (1.53–1.61) 0 1241 (0.7) 418 (1.5) 823 (0.6) 2 2.07 (2.02–2.12) 1 2716 (1.2) 849 (2.3) 1867 (1.0) 3 2.46 (2.40–2.53) 2 3675 (1.7) 1293 (3.3) 2382 (1.3) 4 2.85 (2.77–2.92) 3 3537 (2.2) 1286 (3.8) 2251 (1.8) 5 3.17 (3.08–3.26) 4 2983 (2.8) 1215 (4.5) 1768 (2.2) ≥6 4.41 (4.31–4.52) 5 2096 (3.2) 930 (4.9) 1166 (2.5) Transfusion 1.98 (1.96–2.00) ≥6 4698 (5.1) 2245 (6.6) 2453 (4.3) Pulmonary embolism 1.61 (1.52–1.71) Transfusion Yes 13,069 (3.1) 4861 (6.3) 8208 (2.4) None 7877 (1.3) 3375 (2.4) 4502 (0.9) Pulmonary embolism Combination inpatient database to report seasonal mortal- Yes 494 (7.7) 135 (12.7) 359 (6.7) ity of hip fracture in 425,856 patients [15]. In this study, None 20,452 (2.0) 8101 (3.8) 12,351 (1.5) the 1-year mortality rate for hip fracture was 20.6% in men and 9.5% in women. This compares to previous reports of 21% and 23.9% for hip fracture patients with similar 1-year mortality rates in men [16, 17]. The lower 1-year mortality subtrochanteric fractures had similar mortality rates in both rate for women in this study compared to those observed in sexes, with cervical fractures having a lower mortality rate. previous studies may have been due to the longer life expec- Similarly, compared to cervical fractures, trochanteric and tancy in Japan, as it has more advanced medical technology. subtrochanteric fractures are associated with older age and The 1-year and in-hospital mortality rates tended to increase higher CCI scores [18]. Fracture patterns range from simple with age, with 37.8% of men and 19% of women over 95 to unstable, and patients with unstable fractures may not years of age dying, and the hazard ratio was 5.93, which was be able to load immediately postoperatively, and the longer higher than that in the 65–69 age group. Studies on hip frac- time between surgery and transfer increases complications ture mortality risk have also revealed that age is significantly and mortality [19]. These factors may have contributed to related to mortality [7]. For fracture type, trochanteric and the lower mortality rate in patients with cervical fractures. In 1 3 91 Page 8 of 9 Archives of Osteoporosis (2023) 18:91 addition, because trochanteric and subtrochanteric fractures that transfusion itself may be a risk factor for death. As a are generally treated with internal fixation, the mortality rate result, it is advised to be cautious about intraoperative bleed- of internal fixation was higher than that of hemiarthroplasty ing and to limit postoperative blood transfusions to only or total hip replacement. In a randomized clinical trial com- when absolutely necessary. paring hemiarthroplasty and total hip replacement in patients Although past studies have mainly examined risk factors with hip fracture, patients who underwent total hip replace- for pulmonary embolism because of its low incidence [28, ment had a 58% reduction in 12-month mortality risk [20]. 29], this is the r fi st study to examine the 1-year and in-hospital The patients were matched for age, sex, and pre-fracture mortality rates of hip fracture in cases of pulmonary embo- activity, suggesting that the total hip replacement procedure lism. In particular, we should be concerned about the pre- itself may reduce postoperative mortality. In light of this, vention of deep vein thrombosis in the perioperative period total hip replacement is commonly performed in Japan not since pulmonary embolism increases the mortality rate during only in patients with hip osteoarthritis, but also in patients hospitalization by about four times in both men and women. with numerous daily life activities and relatively young Our study found that male patients from various back- patients with hip fracture. grounds had higher 1-year and in-hospital mortality rates. In terms of surgical delay, if the surgery is performed Although osteoporosis usually affects women, the results after 48 hours of hospitalization, the mortality rate at 3 and suggest that male patients with osteoporosis may be more 12 months after surgery for hip fracture in elderly patients fragile. To our knowledge, no previous study has evaluated increases [21]. Conversely, other studies have shown no effect risk factors for long-term mortality from hip fracture in the on mortality within 30 days [22]. However, there is still no entire Japanese population. Furthermore, this study has very agreement on the relationship between early hip fracture sur- little missing data, so our sample is considered representa- gery and postoperative mortality [23]. In our study, the 1-year tive of the population in this region. mortality rate was slightly higher in the group of patients There are several limitations to this study. First, it is a ret- who underwent surgery after the third day of hospitaliza- rospective study. Second, it was based on an insurance data- tion. This may be due to the fact that the date of injury did base and does not include patients who were not treated by not always coincide with the date of admission, such as in insurance, such as those who had medical assistance for wel- cases of fracture during hospitalization. Although there was fare, compulsory automobile liability insurance, or publicly little difference in 1-year mortality in this study. Shen et al. funded medical care. Finally, several other factors that cannot reported that surgical delay increases postoperative compli- be extracted from the database may also be associated with cations such as pneumonia and myocardial infarction [24]; higher mortality rates, such as secondary osteoporosis caused thus, it is presumably better to perform surgery as early as by steroids, other drugs, or endocrine disorders. The reason for possible. In this study, approximately 60% of both male and this is that this database consists of Japanese claim data, and female patients underwent surgery after the third day of hos- items such as blood test results cannot be determined. Despite pitalization. In Japan, early surgery after a hip fracture injury these limitations, it is assumed that few people are excluded is recommended, but this has not yet been achieved. from the data because most Japanese citizens have medical With regard to CCI, mortality increased progressively insurance, and most patients with hip fractures receive treat- with increasing CCI scores in both men and women, with ment through medical insurance. Therefore, further studies are a particularly high 1-year mortality rate of 30.9% and an needed to investigate other mortality risk factors. in-hospital mortality rate of 6.6% in the group of men with In conclusion, male sex, older age, fracture type (trochan- CCI scores of 6 or higher. Therefore, a high CCI score was teric and subtrochanteric fracture), internal fixation proce- identified as a potential risk factor for 1-year mortality in this dure, delayed operative date, the number of comorbidities, patient population. Previous reports have shown that higher blood transfusion, and pulmonary embolism were signifi- CCI increases both short- and long-term mortality [25], and cantly associated with risk factors for 1-year mortality in this study describes specific mortality rates for each CCI. hip fracture. In addition, men had higher mortality rates than Regarding blood transfusions and pulmonary embolism, women in all categories. In the future, the number of male both significantly increased 1-year and in-hospital mortal- patients with hip fractures will increase with the aging of ity. While some studies reported that transfusions increase society, and medical staff must provide sufficient informa- 1-year mortality by 2.79-fold [26], other studies reported tion before surgery to avoid postoperative mortality. that the difference was not significant when patients were Supplementary Information The online version contains supplemen- matched for background [27]. These results suggest that tary material available at https://doi. or g/10. 1007/ s11657- 023- 01293-z . patients who receive blood transfusions are also likely to have poor preoperative conditions, such as anemia. Acknowledgements We would like to thank Editage (www.editage. com) for English language editing. We greatly appreciate Mitsubishi In this study, the 1-year mortality hazard ratio for trans- Research Institute, Inc. for analytical assistance. fused patients after multivariate analysis was 1.98, suggesting 1 3 Archives of Osteoporosis (2023) 18:91 Page 9 of 9 91 Funding This work was supported by the Health Labour Sciences 12. Charlson ME, Pompei P, Ales KL, MacKenzie CR (1987) A new Research Grant (Grant Number: 20HB1001) and JSPS KAKENHI method of classifying prognostic comorbidity in longitudinal stud- (Grant Numbers: JP20H00623, JP18H04126). ies: development and validation. J Chronic Dis 40:373–383 13. Zhang Z, Yang H, Luo M (2021) Association between Charlson comorbidity index and community-acquired pressure injury in Declarations older acute inpatients in a Chinese tertiary hospital. Clin Interv Aging 16:1987–1995 Ethical approval For this type of study, formal consent is not required. 14. Kubo S, Noda T, Nishioka Y, Myojin T, Nakanishi Y, Furi- hata S, Higashino T, Imamura T (2020) Mortality tracking Conflicts of interest None. using the National Database of Health Insurance Claims and Specific Health Checkups of Japan (NDB). Jpn J Med Inform Open Access This article is licensed under a Creative Commons Attri- 40:319–335 bution 4.0 International License, which permits use, sharing, adapta- 15. 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Journal

Archives of Osteoporosis – Springer Journals

Published: Jul 7, 2023

Keywords: Hip fracture; National database; Health insurance claim database; Mortality; Risk factors

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