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Trends in arthroplasty in Japan by a complete survey, 2014–2017

Open AccessPublished:September 12, 2020DOI:https://doi.org/10.1016/j.jos.2020.07.022

      Abstract

      Background

      Precise knowledge of the prevalence and trends of arthroplasty can facilitate the design of medical plans for efficient treatments. The National Database of Health Insurance Claims and Specific Health Checkups of Japan (NDB) Open Data Japan provides statistics about the annual number of arthroplasties (knee, hip, shoulder, finger, elbow, and foot/ankle) through health insurance claim numbers for these surgeries. The purpose of this study was to document the annual arthroplasty numbers between 2014 and 2017 in Japan and to analyze their four-year trends, gender differences, age distributions, and regional differences as revealed by the complete survey.

      Methods

      Numbers of arthroplasty surgeries were extracted from the NDB Open Data Japan for 2014–2017. For “knee”, “hip”, “shoulder”, “finger”, “elbow”, and “foot/ankle” arthroplasties, we showed the annual arthroplasty numbers, annual arthroplasty numbers by age group, annual arthroplasty numbers in individual prefectures, and annual arthroplasty numbers per 100,000 population in individual prefectures.

      Results

      The annual arthroplasty numbers in 2017 were 146,189 for all joints, 82,304 for knees, 59,029 for hips, 2454 for shoulders, 1551 for fingers, 536 for elbows, and 291 for feet/ankles. For the four years up to 2017, the rate of alteration in the number of arthroplasties was +14% for total arthroplasties, +9% for knees, +21% for hip joints, +97% for shoulders, + 8% for fingers, −10% for elbows, and +25% for feet/ankles. The proportion of females was 70–90% and the peak age was between the late 60s and late 70s for all joints. Variations in arthroplasty numbers per population by prefecture appeared to be small for knees and hips and large for other joints.

      Conclusions

      We revealed the annual total number of arthroplasties for each joint in Japan using the NDB Open Data Japan for the first time.

      1. Introduction

      Arthroplasty is an effective treatment for patients who experience essentially permanent restriction of joint function due to joint destruction that cannot be treated with other methods. Arthroplasty can restore joint function, weight bearing capacity, and quality of life for virtually all joints in the body [
      • Carr A.J.
      • Robertsson O.
      • Graves S.
      • Price A.J.
      • Arden N.K.
      • Judge A.
      • Beard D.J.
      Knee replacement.
      ]. Precise knowledge of the prevalence and trends of arthroplasty facilitates the design of medical plans for efficient treatments.
      In several countries, nationwide registries and large health insurance surveys are now available that provide precise predictions of annual arthroplasty numbers [
      • Maradit Kremers H.
      • Larson D.R.
      • Crowson C.S.
      • Kremers W.K.
      • Washington R.E.
      • Steiner C.A.
      • Jiranek W.A.
      • Berry D.J.
      Prevalence of total hip and knee replacement in the United States.
      ]. In Japan, the annual arthroplasty number has been primarily predicted by private company reports based on a questionnaire survey of the numbers of implants shipped. The Arthroplasty Registry of Japan was launched in 2006 [
      • Akiyama H.
      • Hoshino A.
      • Iida H.
      • Shindo H.
      • Takakura Y.
      • Miura H.
      • Yamamoto K.
      • Yoshiya S.
      • Hasegawa Y.
      • Shimamura T.
      • Kurosaka M.
      • Otsuka H.
      • Kawanabe K.
      • Kawate K.
      • Harada Y.
      • Nakamura T.
      A pilot project for the Japan arthroplasty register.
      ]; however, only 1639 of 3000 hospitals performing orthopedic surgeries were registered as of 2017 [
      • Japanese Society for Replacement Arthroplasty
      Japan arthroplasty register 2017 annual report.
      ], so a complete survey is not currently possible using that registry.
      The National Database of Health Insurance Claims and Specific Health Checkups of Japan (NDB) is one of the most exhaustive health care databases on a national level in the world, and encompasses more than 95% of all arthroplasty claims [
      • Ministry of Health, Labour and Welfare
      ]. The NDB Open Data Japan (NDB-ODJ) provides statistics about the annual numbers of arthroplasties for knees, hips, shoulders, fingers, elbows, and feet/ankles through health insurance claim numbers for these surgeries. The purpose of this study was to document the annual arthroplasty numbers for procedures conducted between 2014 and 2017 in Japan and to analyze their four-year trends, gender differences, age distributions, and regional differences based on this complete survey.

      2. Materials and methods

      In this study, the designation “NDB” refers to the National Database of Health Insurance Claims and Specific Health Checkups of Japan operated by the Ministry of Health, Labour and Welfare, while “NDB-ODJ” refers to the NDB Open Data Japan published as spreadsheets that summarize the claims data. For 2014–2017, we accessed the NDB-ODJ site and downloaded the Excel files “Number of calculations by division, sex, and age group” and “Number of calculations by prefecture” under “operation (code K)” [, , , ]. Three categories of arthroplasty-related surgeries were included: arthroplasty (code K082), removal of arthroplasty (code K082-2), and revision arthroplasty (code K082-3). From each of these three categories, we extracted “knee”, “hip”, “shoulder”, “finger”, “elbow”, “foot”, “hand”, and “acromioclavicular” from the “inpatient” worksheet, and we also extracted “finger” from the “outpatient” worksheet. We ultimately excluded “acromioclavicular” because its annual total number was less than 10 between 2014 and 2017. “Foot” in the NDB-ODJ is described as “foot/ankle” in this paper because it is considered to also include ankle arthroplasties. “Hand” in the NDB-ODJ is described as “hand/wrist” in this paper because it is considered to also include wrist arthroplasties.
      For “knee”, “hip”, “shoulder”, “finger”, “elbow”, and “foot/ankle”, we showed the annual arthroplasty numbers, annual arthroplasty numbers by age group, annual arthroplasty numbers in individual prefectures, and annual arthroplasty numbers per 100,000 population in individual prefectures. For “hand/wrist”, no specific values were shown for gender, age and prefecture that included fewer than 10 cases; therefore, no detailed analyses were performed.
      The numbers of males who underwent each type of arthroplasty were calculated by summing the number for each age group at five year intervals. The female numbers were summarized in the same way. Specific male (or female) numbers were not shown for arthroplasty types with fewer than 10 patients; these “unknown” gender numbers were obtained by subtracting the male numbers and female numbers from the total numbers.
      The annual arthroplasty numbers per 100,000 population in individual prefectures in 2017 were determined from the population in each prefecture obtained from “Table: Population by Sex and Sex ratio for Prefectures – Total population, Japanese population, October 1, 2017,” which provides the population estimates released by the Statistics Bureau, Ministry of Internal Affairs and Communications [
      • Statistics Bureau of Japan
      Population by sex and sex ratio for prefectures – total population, Japanese population, October 1, 2017.
      ]. The average value was calculated as the ratio of total arthroplasty numbers to the total population in Japan for database cells that showed numbers.
      The percentage of arthroplasty removals was depicted as the ratio of the number of removals to the number of primary arthroplasties in the same year. The percentage of arthroplasty revisions was also shown as the ratio of the number of arthroplasty revisions to the number of primary arthroplasties in the same year.

      3. Results

      3.1 Arthroplasty in all joints

      The total number of arthroplasties for all joints was 128,065 in 2014 and this number increased gradually to 146,189 in 2017 (Fig. 1A). Knee arthroplasty accounted for the highest percentage, at 56.3%, hip arthroplasty was the second highest at 40.4%, and both knee and hip arthroplasties accounted for 97% of the total arthroplasties conducted in 2017 (Fig. 1B). Shoulder arthroplasties accounted for 1.7%, finger arthroplasties for 1.1%, and elbow, foot/ankle, and hand/wrist arthroplasties for less than 1.0%. As for age, the highest was in the late 70s (Fig. 1C). The proportion of elders aged 65 and older was almost 80%; elders aged 65–74 accounted for 33.7% and that aged 75 and older accounted for 45.9% (Fig. 1D).
      Fig. 1
      Fig. 1Prevalence of arthroplasties in all joints between 2014 and 2017 in Japan based on the NDB-ODJ. (A) Annual arthroplasty numbers in all joints. (B) Percentage of arthroplasties for knee, hip, shoulder, finger, elbow, foot/ankle and hand/wrist in 2017. (C) Annual arthroplasty numbers by age group. (D) Percentage of arthroplasties age group in 2017.

      3.2 Knee arthroplasty

      The total number of knee arthroplasties was 75,635 in 2014; these numbers fluctuated slightly and then increased to 82,304 in 2017 (Fig. 2A). The proportion of female cases was close to 80%. The peak age was late 70s (Fig. 2B). The highest numbers of knee arthroplasty occurred in the Osaka, Tokyo, and Hokkaido prefectures (Fig. 2C). The numbers of knee arthroplasties per population by prefecture showed relatively small variations (Fig. 2D).
      Fig. 2
      Fig. 2Prevalence of knee arthroplasties between 2014 and 2017 in Japan based on the NDB-ODJ. (A) Annual numbers of knee arthroplasties. Total numbers are shown above the bar, and the percentages inside the dark bars indicate the female cases. (B) Annual numbers of knee arthroplasties by age group. (C) Annual numbers of knee arthroplasties in individual prefectures. (D) Annual numbers of knee arthroplasties per 100,000 population in individual prefectures in 2017. The dotted line indicates the average values.

      3.3 Hip arthroplasty

      The total number of hip arthroplasties was 48,921 in 2014 and increased to 59,029 in 2017 (Fig. 3A). The proportion of female cases was close to 83%. The peak age was late 60s (Fig. 3B). The highest numbers of hip arthroplasties occurred in the Tokyo, Osaka, Kanagawa, and Hokkaido prefectures (Fig. 3C). The numbers of hip arthroplasties per population by prefecture showed small variations (Fig. 3D). As hip hemiarthroplasties mainly performed for fractures, numbers of hip hemiarthroplasties were not included in those of hip arthroplasties, which were shown Supplementary Fig. 1.
      Fig. 3
      Fig. 3Prevalence of hip arthroplasties between 2014 and 2017 in Japan based on the NDB-ODJ. (A) Annual numbers of hip arthroplasties. Total numbers are shown above the bar, and the percentages inside the dark bars indicate the female cases. (B) Annual numbers of hip arthroplasties by age group. (C) Annual numbers of hip arthroplasties in individual prefectures. (D) Annual numbers of hip arthroplasties per 100,000 population in individual prefectures in 2017. The dotted line indicates the average values.

      3.4 Shoulder arthroplasty

      The total number of shoulder arthroplasties was 1246 in 2014 and increased to 2454 in 2017 (Fig. 4A). The proportion of female cases was close to 70%. The peak age was late 70s (Fig. 4B). The highest numbers of shoulder arthroplasties occurred in the Chiba, Tokyo, Osaka, and Hokkaido prefectures (Fig. 4C). The numbers of shoulder arthroplasties per population by prefecture had a relatively large variation (Fig. 4D).
      Fig. 4
      Fig. 4Prevalence of shoulder arthroplasties between 2014 and 2017 in Japan based on the NDB-ODJ. (A) Annual numbers of shoulder arthroplasties. Total numbers are shown above the bar, and the percentages inside the dark bars indicate the female cases. (B) Annual numbers of shoulder arthroplasties by age group. (C) Annual numbers of shoulder arthroplasties in individual prefectures. ∗Prefectures with fewer than 10 arthroplasties through the years. (D) Annual numbers of shoulder arthroplasties per 100,000 population in individual prefectures in 2017. ∗Prefectures with fewer than 10 arthroplasties in 2017.

      3.5 Finger arthroplasty

      The total number of finger arthroplasties was 1436 in 2014, and these numbers decreased and then increased to 1551 in 2017 (Fig. 5A). The proportion of female cases was 85–89%. In 2017, the proportion of outpatients was 19.7% (Fig. 5B). The peak age was early 70s (Fig. 5C). Many finger arthroplasties were performed in the Tokyo and Osaka prefectures, and no or fewer than 10 of these arthroplasties (∗) were performed in 30% of the prefectures in the 4 study years (Fig. 5D). The numbers of finger arthroplasties per population by prefecture had a large variation (Fig. 5E).
      Fig. 5
      Fig. 5Prevalence of finger arthroplasties between 2014 and 2017 in Japan based on the NDB-ODJ. (A) Annual numbers of finger arthroplasties. Total numbers are shown above the bar, and the percentages inside the dark bars indicate the female cases. (B) Percentages of arthroplasties for outpatients and inpatients in 2017. (C) Annual numbers of finger arthroplasties by age group. (D) Annual numbers of finger arthroplasties in individual prefectures. ∗Prefectures with fewer than 10 arthroplasties through the years. (E) Annual numbers of finger arthroplasties per 100,000 population in individual prefectures in 2017. ∗Prefectures with fewer than 10 arthroplasties in 2017.

      3.6 Elbow arthroplasty

      The total number of elbow arthroplasties was 594 in 2014 and the number decreased to 536 in 2017 (Fig. 6A). The proportion of female cases was 80–83%. The peak age was early 70s (Fig. 6B). Many elbow arthroplasties were performed in the Tokyo and Osaka prefectures, and no or fewer than 10 of these arthroplasties (∗) were performed in 49% of the prefectures in the 4 study years (Fig. 6C). The numbers of elbow arthroplasties per population by prefecture had a large variation (Fig. 6D).
      Fig. 6
      Fig. 6Prevalence of elbow arthroplasties between 2014 and 2017 in Japan based on the NDB-ODJ. (A) Annual numbers of elbow arthroplasties. Total numbers are shown above the bar, and the percentages inside the dark bars indicate the female cases. (B) Annual numbers of elbow arthroplasties by age group. (C) Annual numbers of elbow arthroplasties in individual prefectures. ∗Prefectures of which an arthroplasty number was fewer than 10 through the years. (D) Annual numbers of elbow arthroplasties per 100,000 population in individual prefectures in 2017. ∗Prefectures of which an arthroplasty number was fewer than 10 in 2017.

      3.7 Foot/ankle arthroplasty

      The total number of foot/ankle arthroplasties was 233 in 2014, and it fluctuated over the years, finally increasing to 291 in 2017 (Fig. 7A). The proportion of female cases was 70–79%. The peak age was early to late 70s (Fig. 7B). Many foot/ankle arthroplasties were performed in the Nara and Tokyo prefectures, and no or fewer than 10 of these arthroplasties (∗) were performed in 81% of the prefectures in the 4 study years (Fig. 7C). The numbers of foot/ankle arthroplasties per population by prefecture showed a markedly large variation (Fig. 7D).
      Fig. 7
      Fig. 7Prevalence of foot/ankle arthroplasties between 2014 and 2017 in Japan based on the NDB-ODJ. (A) Annual numbers of foot/ankle arthroplasties. Total numbers are shown above the bar, and the percentages inside the dark bars indicate the female cases. (B) Annual numbers of foot/ankle arthroplasties by age group. (C) Annual numbers of foot/ankle arthroplasties in individual prefectures. ∗Prefectures of which an arthroplasty number was fewer than 10 through the years. (D) Annual numbers of foot/ankle arthroplasties per 100,000 population in individual prefectures in 2017. ∗Prefectures of which an arthroplasty number was fewer than 10 in 2017.

      3.8 Arthroplasty removals and revisions

      The rate for arthroplasty removal was 0.6–0.7% in the knee, 1.0–1.1% in the hip joint, 0.7–2.1% in the shoulder, 2.2–2.7% in the finger, 5.6–8.8% in the elbow, and 4.9% in the foot/ankle (Table 1). The rate for arthroplasty revision was 1.9–2.1% in the knee, 4.5–5.7% in the hip joint, 2.2–5.6% in the shoulder, 3.9–6.7% in the finger, 15.0–20.5% in the elbow, and 4.0–6.7% in the foot/ankle.
      Table 1Annual number of primary arthroplasties, arthroplasty removals, and revision arthroplasties based on the NDB-ODJ (2014–2017).
      2014201520162017
      Knee
       Primary75,63577,04476,95582,304
       Removal505 (0.7%)538 (0.7%)505 (0.6%)533 (0.6%)
       Revision1,562 (2.1%)1,557 (2.0%)1,578 (2.1%)1,587 (1.9%)
      Hip
       Primary48,92151,76552,52859,029
       Removal538 (1.1%)548 (1.1%)522 (1.0%)629 (1.1%)
       Revision2,788 (5.7%)2,784 (5.4%)2,788 (5.3%)2,643 (4.5%)
      Shoulder
       Primary1,2461,5782,0092,454
       Removal26 (2.1%)11 (0.7%)25 (1.2%)16 (0.7%)
       Revision35 (2.8%)45 (2.9%)113 (5.6%)55 (2.2%)
      Finger
       Primary1,4361,3941,3241,551
       Removal33 (2.3%)38 (2.7%)30 (2.3%)34 (2.2%)
       Revision56 (3.9%)69 (4.9%)68 (5.1%)104 (6.7%)
      Elbow
       Primary594576560536
       Removal33 (5.6%)38 (6.6%)43 (7.7%)47 (8.8%)
       Revision89 (15.0%)103 (17.9%)113 (20.5%)108 (20.1%)
      Foot/ankle
       Primary233247238291
       Removal12 (4.9%)
       Revision14 (6.0%)10 (4.0%)16 (6.7%)13 (4.5%)
      Hand/wrist
       Primary1524
       RemovalN/AN/A
       RevisionN/AN/A
      Percentage for removal is the ratio of the number of removals to the number of primary arthroplasties in the same year. Percentage for revision is the ratio of the number of revision arthroplasties to the number of primary arthroplasties in the same year. –: Under 10 cases. N/A: not available.

      4. Discussion

      For the four years between 2014 and 2017, the rate of change in the number of arthroplasties was +14% for total arthroplasties, +9% for knees, +21% for hip joints, +97% for shoulders, +8% for fingers, −10% for elbows, and +25% for feet/ankles. Over the same period, the population aged 65 and over increased by 12% [
      • Statistics Bureau of Japan
      Population by age (five-year groups and 3 groups) and sex (as of October 1 of each year) – total population, Japanese population (from 2000 to 2015).
      ,
      • Statistics Bureau of Japan
      Population and percentage distribution by age (5-year age group) and sex – total population.
      ], as did the number of knee arthroplasties. The rate of increase in the number of hip arthroplasties was about twice that of the increase in the elderly population, which may be due to expansion of the indications for hip arthroplasties because of good clinical outcomes [
      • Smith L.K.
      • Dures E.
      • Beswick A.D.
      Systematic review of the clinical effectiveness for long-term follow-up of total hip arthroplasty.
      ]. The number of shoulder arthroplasties doubled, which probably reflects the increased popularity of reverse shoulder arthroplasty. The number of finger arthroplasties increased slightly, whereas the number of elbow arthroplasties decreased, probably because rheumatoid arthritis patients, who were previously good candidates for these operations, have declined surgery in favor of the advances in biologics [
      • Aletaha D.
      • Smolen J.S.
      Diagnosis and management of rheumatoid arthritis: a review.
      ]. The increase in foot/ankle arthroplasties is due to the increase in the number of specific hospitals.
      Clear gender differences were evident for arthroplasties, as the proportion of females was 70–90% for all joints and was especially high for fingers and lower for shoulders. The peak ages for arthroplasty were the late 60s, mostly for hip joint arthroplasties, and the late 70s, mostly for knee and shoulder arthroplasties.
      The numbers of arthroplasties per population by prefecture showed small variations for joints that underwent a large amount of arthroplasty and large variations for joints that underwent a small amount of arthroplasty. However, comparison of the knee and hip joints showed a smaller variability although the arthroplasty numbers were smaller for the hip joint. This suggests a more stable surgical indication for the hip joint and that the indication for surgery in each prefecture is more constant in the hip than in the knee.
      The rates for the arthroplasty removals and revisions were highest in the elbow, which may be the reason why the number of elbow arthroplasties decreased for the four study years. However, the results of this analysis must be interpreted cautiously because the rate for the removal was calculated as the ratio of the number of removals to the number of primary arthroplasties in the same year. The rate for revision arthroplasties was calculated in the same way. Survival rates cannot be determined unless the same patient is followed continuously. According to six registry studies of elbow arthroplasties, the 10-year survival rate was 81–90% [
      • Frankle M.A.
      • Herscovici Jr., D.
      • DiPasquale T.G.
      • Vasey M.B.
      • Sanders R.W.
      A comparison of open reduction and internal fixation and primary total elbow arthroplasty in the treatment of intraarticular distal humerus fractures in women older than age 65.
      ,
      • Jenkins P.J.
      • Watts A.C.
      • Norwood T.
      • Duckworth A.D.
      • Rymaszewski L.A.
      • McEachan J.E.
      Total elbow replacement: outcome of 1,146 arthroplasties from the Scottish arthroplasty project.
      ,
      • Krukhaug Y.
      • Hallan G.
      • Dybvik E.
      • Lie S.A.
      • Furnes O.N.
      A survivorship study of 838 total elbow replacements: a report from the Norwegian Arthroplasty Register 1994–2016.
      ,
      • Nestorson J.
      • Rahme H.
      • Adolfsson L.
      Arthroplasty as primary treatment for distal humeral fractures produces reliable results with regards to revisions and adverse events: a registry-based study.
      ,
      • Plaschke H.C.
      • Thillemann T.M.
      • Brorson S.
      • Olsen B.S.
      Implant survival after total elbow arthroplasty: a retrospective study of 324 procedures performed from 1980 to 2008.
      ,
      • Skytta E.T.
      • Eskelinen A.
      • Paavolainen P.
      • Ikavalko M.
      • Remes V.
      Total elbow arthroplasty in rheumatoid arthritis: a population-based study from the Finnish arthroplasty register.
      ].
      Some open questions are the accuracy of the NDB-ODJ and the percentage of arthroplasties that are covered. The national health insurance program in Japan had accumulated at least 95% of the health insurance claims for the NDB in May 2015. The accumulation ratio for hospitals with over 19 beds is 99.9% since May 2013. According to the commentary section of the first NDB-ODJ in publication format, the NDB is one of the most exhaustive national healthcare databases in the world, and the data comprises almost all the claims in Japan under universal health insurance. Japanese health insurance does not cover all arthroplasties, but it covers more than 95% of the arthroplasties performed in Japan.
      In Japan, the diagnosis procedure combination (DPC) database is also available to a limited extent. All academic hospitals are obliged to contribute to that database, but participation by community hospitals is voluntary. In 2014, 1133 hospitals participated and provided data for 7.82 million patients, representing 56.4% of all inpatient admissions to acute care hospitals in Japan. The DPC database provides more detailed information containing discharge abstracts and administrative reimbursement data for inpatient episodes, but it is an extraction survey and approval by the Institutional Review Board is required to access the data. Kawata et al. reported annual trends in knee arthroplasty and tibial osteotomy between 2007 and 2014 through an analysis of the DPC database [
      • Kawata M.
      • Sasabuchi Y.
      • Inui H.
      • Taketomi S.
      • Matsui H.
      • Fushimi K.
      • Chikuda H.
      • Yasunaga H.
      • Tanaka S.
      Annual trends in knee arthroplasty and tibial osteotomy: analysis of a national database in Japan.
      ]. They reported 36,794 knee arthroplasties in 2014, which is equivalent to 49% of the total knee arthroplasties in the NDB-ODJ for the same year. Unlike the NDB, the DPC data also provide the procedure (total knee arthroplasty or unicompartmental knee arthroplasty) and primary disease (osteoarthritis, osteonecrosis, or rheumatoid arthritis).
      Pabinger et al. compared the annual number of knee arthroplasties per 100,000 population in 24 OECD countries as reported in 2015 [
      • Pabinger C.
      • Geissler A.
      Utilization rates of hip arthroplasty in OECD countries.
      ]. Unfortunately, Japan was not included in that report, possibly because those statistics had not been reported in academic publications at that time. Here, we revealed that the annual number of knee arthroplasties per 100,000 population was 61 in Japan in 2017, which placed Japan 21st out of the 25 OECD countries. The United States had the highest number, at 235, whereas Korea, the only Asian country listed in that paper, was 15th out of 25, with 110 knee arthroplasties. As exemplified here, these statistics are useful for various analyses related to arthroplasty.
      We propose three limitations in this study. The first is that the NDB Open Data Japan does not provide diagnosis, surgical procedures, and implant models. By contrast, the Japan Arthroplasty Register provides these data even though the annual number of arthroplasties in 2017 was 35,870 (44% compared to NDB Open Data Japan) for knees, and 30,238 (51%) for hips [
      • Japanese Society for Replacement Arthroplasty
      Japan arthroplasty register 2017 annual report.
      ]. Combining the data from both registries allows us to determine the annual number of cases per diagnosis, surgical procedure, and implant model. The second limitation is that the minimum unit based on privacy protection and security policy is 10, so if only small numbers of arthroplasties were performed, information such as age, gender, and prefecture is not available. The third limitation is that the arthroplasty surgery numbers we analyzed did not include subjects who were injured in traffic accidents or occupational accidents or those who had made claims for automobile liability insurance or industrial injury insurance. However, the number of these subjects is potentially much smaller than the number who filed health insurance claims.
      In conclusion, we analyzed the annual arthroplasty numbers between 2014 and 2017 in Japan using the complete NDB-ODJ, the exhaustive survey of health insurance claims. The annual arthroplasty number in 2017 was 146,189 for all joints, 82,304 for knees, 59,029 for hips, 2454 for shoulders, 1551 for fingers, 536 for elbows, and 291 for feet/ankles. For the four years up to 2017, the rate of increase in the number of arthroplasties was 14% for total arthroplasties, 9% for knees, 21% for hip joints, and 97% for shoulders. We revealed the annual total number of arthroplasties for each joint in Japan using the NDB Open Data Japan for the first time.

      Author contributions

      HKa: Conception and design. Data collection and analysis. Manuscript writing. NO: Data interpretation. YK: Data interpretation. YN: Data interpretation. HKo: Data interpretation. TW: Data interpretation. TJ: Data interpretation. IS: Data organization, manuscript completion, and final approval.

      Declaration of competing interest

      The authors declare that they have no conflicts of interest.

      Acknowledgements

      This work was supported by the Grants-in-Aid for Scientific Research of Japan Society for the Promotion of Science , Grant Number JP18K09095 . We appreciate Ms. Amy Marton and Ms. Ellen Roider for English editing. We thank Kimiko Takanashi for technical assistance with the data collection.

      Appendix A. Supplementary data

      The following is the Supplementary data to this article:
      • Multimedia component 1

        Prevalence of hip hemiarthroplasties between 2014 and 2017 in Japan based on the NDB-ODJ. (A) Annual numbers of hip hemiarthroplasties. Total numbers are shown above the bar, and the percentages inside the dark bars indicate the female cases. (B) Annual numbers of hip hemiarthroplasties by age group. (C) Annual numbers of hip hemiarthroplasties in individual prefectures. ∗Prefectures of which a hemiarthroplasty number was fewer than 10 through the years. (D) Annual numbers of hip hemiarthroplasties per 100,000 population in individual prefectures in 2017. ∗Prefectures of which a hemiarthroplasty number was fewer than 10 in 2017.

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