Age and Regional Trends in Groin Hernia Surgery in Japan: An Analysis of Laparoscopic Repair, Outpatient Surgery, and Manual Reduction Using National Database Open Data.

Masanori Sato: writing – original draft, conceptualization, methodology, data curation, formal analysis, visualization, writing – review and editing. Kyosuke Miyazaki: writing – review and editing. Tatsuya Tazaki: writing – review and editing. Itsuro Nagae: writing – review and editing. Taketo Matsubara: writing – review and editing. Saseem Poudel: writing – review and editing, conceptualization. Tsuyoshi Takagi: writing – review and editing. Hidetoshi Wada: writing – review and editing, conceptualization.

This study used only publicly available aggregated data from the NDB Open Data of Japan and official national statistics. In accordance with national ethical guidelines, institutional ethical review was not required.

The authors have nothing to report.

Data were obtained from the publicly available open data of the NDB, which are provided as separate files corresponding to short‐stay surgery, outpatient surgery, and inpatient surgery for each fiscal year from 2014 to 2023 [ 5 ]. For each dataset, age‐ and sex‐stratified data and prefecture‐level aggregated data were available; however, counts fewer than 10 were suppressed in the original datasets, and these values were treated as zero in the present analysis. Surgical procedures in the database are classified by hernia type and surgical approach (laparoscopic or open), with inguinal hernia procedures further subdivided according to the presence of pediatric‐related add‐on reimbursements. These categories were appropriately aggregated to construct the analytical dataset. In this study, the number of surgeries was defined based on insurance claims that included procedure codes for inguinal or femoral hernia repair, with each claim treated as one surgical procedure. Population data stratified by age and sex, and prefecture were obtained from official population statistics published by the Statistics Bureau of Japan, using October 1 of each fiscal year as the reference date [ 10 ]. For years prior to 2020, prefecture‐level population data by 5‐year age group were provided in units of thousands. Age‐adjusted surgery rates were calculated using direct standardization with the Japanese standard population and expressed per 100 000 population. To account for differences in age and sex distributions across prefectures, indirect standardization was applied. National age‐ and sex‐specific groin hernia surgery rates derived from NDB open data were used to estimate the expected number of surgeries for each prefecture based on official population statistics, and the standardized surgery ratio (SSR) was calculated as the ratio of observed to expected surgeries. Because indirect standardization used aggregated open data with different stratification levels, the nationwide SSR is not constrained to be exactly 1.0. For descriptive visualization of temporal trends, selected fiscal years (2015, 2017, 2019, 2021, and 2023) were presented. Lifetime surgical burden was estimated by summing age‐ and sex‐specific surgery rates (per 100 000 population per year) multiplied by 5‐year age intervals across the lifespan, using NDB open data. The oldest age category (≥ 90 years) was approximated as a 5‐year interval. This measure reflects cumulative surgical activity rather than the lifetime probability of surgery. Age‐ and sex‐specific laparoscopic surgery rates were calculated as the proportions of groin hernia repairs performed using a laparoscopic approach within each age and sex category for each fiscal year from 2014 to 2023. For prefecture‐level analyses, laparoscopic surgery rates were calculated for each prefecture and fiscal year as the proportion of laparoscopic procedures among all groin hernia surgeries. Outpatient surgery rates for groin hernia repair were defined as the proportion of outpatient procedures among all groin hernia surgeries and were calculated for each fiscal year from 2014 to 2023 by age and sex, as well as at the prefecture level. In the NDB, outpatient surgery refers to procedures reimbursed on a fee‐for‐service basis without hospitalization or short‐stay surgery fees, whereas procedures reimbursed under the short‐stay surgery system or performed in Diagnosis Procedure Combination hospitals are not classified as outpatient surgery, even when clinically conducted as same‐day procedures. Accordingly, the outpatient surgery rate reflects a reimbursement‐based classification rather than the overall prevalence of clinical day surgery. To characterize manual reduction for groin hernia, three complementary measures were constructed. First, population‐based manual reduction rates were calculated as the number of manual reduction procedures per 100 000 population by age and sex. Second, the Manual Reduction Index (MRI) was defined as the ratio of manual reduction procedures to total groin hernia surgeries within each analytical stratum; because surgical volume does not represent a true population‐at‐risk denominator, the MRI does not estimate incarceration incidence but serves as a relative indicator of manual reduction activity in relation to surgical volume. Third, using population‐based rates, the lifetime manual reduction burden after adulthood (≥ 20 years) was estimated by summing age‐ and sex‐specific rates multiplied by 5‐year age intervals. Because manual reduction is an administrative claim‐based measure, repeated procedures in the same individual may be included, cases treated by immediate emergency surgery may be omitted, and procedures performed without reimbursement claims may not be captured in the database. For prefecture‐level analyses, surgery rates, laparoscopic surgery rates, outpatient surgery rates, and the MRI were calculated for each prefecture and fiscal year. These measures were visualized as choropleth maps of Japan using Datawrapper ( https://www.datawrapper.de ). One‐sample t ‐tests were used to compare the total number of hernia surgeries in fiscal years 2020 and 2021 with those in the remaining years. To examine long‐term trends unaffected by the COVID‐19 pandemic, fiscal years 2020–2021 were excluded a priori, and linear regression analysis was performed with fiscal year as a continuous variable. All statistical analyses were performed using EZR 1.42 (Saitama Medical Center, Jichi Medical University, Saitama, Japan) [ 11 ].

Annual numbers of groin and femoral hernia surgeries in Japan from fiscal year 2014 to 2023 are shown in Figure  1 , with the corresponding numerical values provided in Table  S1 . The total number of hernia surgeries in fiscal year 2020 was significantly lower than in the other years (131 605 vs. mean 149 372 cases; one‐sample t ‐test, p  < 0.001). In fiscal year 2021, surgical volume increased compared with 2020 but remained significantly lower than in the other years (139 356 vs. mean 148 511 cases; one‐sample t ‐test, p  = 0.003). Excluding fiscal years 2020–2021, linear regression showed a modest upward trend in total hernia surgeries (+850 cases per year), without statistical significance ( p  = 0.086). Temporal trends in the number of inguinal and femoral hernia surgeries by surgical approach in Japan (2014–2023). Stacked bars indicate the annual numbers of inguinal and femoral hernia surgeries, stratified by hernia type (inguinal or femoral) and surgical approach (open or laparoscopic). Age‐ and sex‐specific rates of inguinal hernia surgery exhibited a bimodal distribution, with one peak in early childhood and a second peak in older age groups (Figure  2a and Table  S2 ). In males, surgery rates consistently peaked in the 75–79 and 80–84 age groups throughout the study period. Although year‐to‐year variability was observed in these older age groups, exclusion of the COVID‐19–affected years revealed a progressive increase in surgery rates within these peak age categories over time. In females, surgery rates were lower than in males across most age groups, with a similar but less pronounced increase in older age. Age‐ and sex‐specific rates of hernia surgery per 100 000 population. Age‐specific rates of hernia surgery per 100 000 population are shown for selected fiscal years. Left panel shows rates of inguinal hernia surgery (a), and right panel shows rates of femoral hernia surgery (b). Solid lines represent males, and dashed lines represent females. Line colors correspond to fiscal years as indicated in the legend. Age groups are shown in 5‐year intervals, with a separate category for patients aged ≥ 90 years. Age‐ and sex‐specific rates of femoral hernia surgery were negligible in younger age groups and increased progressively with age in both sexes (Figure  2b and Table  S3 ). Surgery rates were consistently higher in females than in males, with a marked rise observed in older age groups, particularly after 70 years of age. A temporary decline in surgery rates was observed in 2020, followed by partial recovery in subsequent years. Over 2014–2023, the mean lifetime surgical burden per 100 000 population was 21 432 in males and 3861 in females. The total burden ranged from 19 416 to 23 341 in males and from 3245 to 4867 in females. Prefecture‐level SSRs for groin hernia surgery exhibited a reproducible geographic pattern across fiscal years (Figure  3a and Table  S4 ). Prefectures with lower SSRs were predominantly non‐metropolitan, whereas those with higher SSRs were not confined to urban areas. Despite modest year‐to‐year variation in absolute values, the relative ranking of prefectures was largely maintained over time. Ranking based on the mean SSR over 2014–2023 further demonstrated persistent regional differences, with several non‐metropolitan prefectures included among those with higher long‐term SSRs (Figure  3b,c ). Geographic variation in age‐ and sex‐standardized groin hernia surgery rates across Japanese prefectures. Choropleth maps illustrate prefecture‐level standardized surgery rates (a). Rates were directly standardized for age and sex using the national population as the reference. The top 10 (b) and the bottom 10 (c) prefectures are shown in the panels, according to the mean standardized surgery rate over the period 2014–2023. Horizontal bars represent prefecture‐specific standardized rates, and the dashed vertical line indicates the national average. At the national level, the proportion of laparoscopic procedures among groin and femoral hernia surgeries increased steadily over the study period, rising from 24.6% in 2014 to 54.2% in 2023, indicating a marked nationwide shift toward laparoscopic approaches. This upward trend persisted during the COVID‐19–affected years (2020–2021), with laparoscopic rates of 44.6% and 47.6%, respectively, and exceeded 50% after 2022. Age‐ and sex‐specific analyses demonstrated distinct and reproducible patterns (Figure  4a,b and Table  S5 ). In males, laparoscopic rates showed a broad unimodal distribution with a peak in young adulthood (35–39 years) and a consistent trough at 15–19 years across all examined years, with progressive increases over time in all age groups. In females, laparoscopic rates exhibited a bimodal pattern, with peaks at 10–14 years and 55–69 years and a trough in the 20–25‐year age range. Temporal increases were evident at both peaks, whereas age groups corresponding to the trough showed only limited increases. Marked geographic variation in laparoscopic repair rates was observed at the prefectural level (Figure  4c and Table  S6 ). Across the study period, prefecture‐level laparoscopic rates ranged from approximately 25% to over 80%, and the relative ranking of prefectures was largely preserved over time. Lower laparoscopic rates were more frequently observed in the Tohoku region, whereas higher rates were observed in several prefectures in western Japan, including the Kansai and Kyushu regions. Laparoscopic groin hernia repair rates by age, sex, and region. Age‐ and sex‐specific laparoscopic repair rates are shown for males (a) and females (b) in selected fiscal years. Geographic distribution of laparoscopic repair rates by prefecture is shown for 2015, 2019, and 2023 (c). For regional maps, a unified color scale based on the minimum, median, and maximum values observed over the entire study period was applied. Age‐specific outpatient surgery rates for groin hernia repair demonstrated a consistent pattern across fiscal years (Figure  5a ). Outpatient rates increased from childhood to young adulthood, peaked in the 20–34‐year age range, and then declined progressively with increasing age. Across all age groups, outpatient surgery rates increased over time, with the highest values observed in 2023. The magnitude of increase was most pronounced in young and middle‐aged adults, whereas outpatient rates remained low in older age groups, particularly among patients aged 70 years and older (Table  S7 ). Outpatient groin hernia surgery rates by age and region. Age‐specific outpatient surgery rates are shown for selected fiscal years (a). Geographic distribution of outpatient surgery rates by prefecture is shown for 2015, 2019, and 2023 (b). A unified color scale was applied to facilitate comparison across regions, with the national outpatient surgery rate in 2015 used as the reference. Prefecture‐level outpatient surgery rates showed marked geographic variation across fiscal years (Figure  5b and Table  S8 ). In 2015, outpatient surgery was concentrated in a limited number of prefectures, whereas by 2019 and 2023, higher outpatient rates were observed in an increasing number of regions relative to the national reference. Sex‐ and age‐specific analyses revealed distinct patterns of manual reduction between males and females (Figure  6 ). Using population‐based manual reduction rates per 100 000 population, values in both sexes were highest in early childhood, declined sharply to near‐zero levels during adolescence and young adulthood, and remained low across most adult age groups. In advanced age, population‐based rates increased again in both sexes, with a marked rise in males and a more modest but consistent increase in females, particularly among those aged ≥ 80 years (Figure  6a and Table  S9 ). The MRI showed a broadly similar age‐related pattern but demonstrated a clearer sex difference in older age groups. MRI values remained low and relatively stable in males throughout adulthood, whereas in females, they increased progressively from middle age onward, resulting in substantially higher MRI values in elderly females than in males of corresponding age groups (Figure  6b and Table  S10 ). Age‐ and regional patterns of manual reduction for groin hernia in Japan. Age‐ and sex‐specific population‐based manual reduction rates per 100 000 population are shown in (a). The MRI, defined as the ratio of manual reductions to groin hernia surgeries, is shown by age and sex in (b). Because age‐specific curves overlapped across years, pooled data from 2014 to 2023 are shown. Panel (c) shows the prefecture‐level distribution of population‐based manual reduction rates in 2015, 2019, and 2023. Choropleth maps display relative differences across prefectures, with color scales standardized within each year using the national rate as a reference. Prefecture‐level analyses showed marked geographic variation in population‐based manual reduction rates per 100 000 population, with stable clusters of high and low rates across fiscal years (Figure  6c and Table  S11 ). These patterns were largely preserved over time and were not explained by differences in population aging, indicating regional variation in manual reduction practices rather than demographic shifts. Using population‐based manual reduction rates, the estimated lifetime manual reduction burden after adulthood (≥ 20 years) was 2431.05 per 100 000 population in males and 713.60 per 100 000 population in females.

In Japan, virtually all groin hernia surgeries except robot‐assisted repair are covered by the universal health insurance system. Because robot‐assisted procedures accounted for only 0.7% of cases in 2023 and electronic claims submission exceeded 99.9% since 2015, the NDB cohort represents over 99% of surgically treated cases nationwide [ 12 ]. The marked reduction in total hernia surgeries observed in 2020 is likely attributable to the COVID‐19 pandemic. A nationwide study from the Swedish Hernia Register reported a similar decline in groin hernia repair volumes, suggesting that the extent of surgical reduction in Japan was broadly comparable to that observed internationally during the pandemic [ 13 ]. When the COVID‐19‐affected years (2020–2021) were excluded, the overall volume of hernia surgery demonstrated a gradual upward trend. This pattern suggests a temporary disruption in healthcare delivery rather than a sustained change. When age‐ and sex‐standardized surgery rates were examined over time, inguinal hernia surgery showed a progressive year‐on‐year increase in the 75–84‐year age group, whereas rates in most other age groups remained largely stable. This increase may partly reflect improvements in healthy life expectancy in Japan, along with advances in perioperative care and surgical techniques that have expanded the feasibility of elective surgery in older adults [ 14 , 15 , 16 ]. In addition, wider dissemination of surgical indications and institutional promotion of hernia repair in older adults may have contributed to this trend [ 17 ]. In contrast, age‐ and sex‐standardized surgery rates in most other age groups showed minimal temporal variation and highly consistent age‐ and sex‐specific patterns over time, suggesting stable, age‐dependent surgical demand. Although the overall age‐specific curve resembles that reported in the Danish nationwide study, which showed a bimodal distribution, absolute values are not directly comparable because the Danish analysis reported a 5‐year person‐based prevalence, whereas the present study used annual, procedure‐based surgery rates [ 9 ]. This temporal consistency supports the use of nationwide surgical data for analyses of cumulative surgical burden. Integration of age‐ and sex‐specific surgery rates across the lifespan revealed marked sex‐specific differences in the lifetime surgical burden of groin hernia in Japan. Over 2014–2023, the mean lifetime surgical burden corresponded to approximately 21.4 surgeries per 100 males and 3.9 surgeries per 100 females, indicating a 5.6‐fold higher cumulative surgical burden in males. These findings are directionally consistent with previous life table‐based estimates suggesting that approximately 27% of men and 3% of women will undergo inguinal hernia repair over their lifetime [ 18 ]. However, unlike lifetime risk estimates, the present measure summarizes population‐level cumulative surgical demand rather than individual probability, which is particularly relevant in an aging society. The temporal reproducibility of prefecture‐level SSRs indicates stable, systematic regional variation in groin hernia surgery rates beyond age and sex structure. Although lower SSRs were more frequently observed in non‐metropolitan prefectures, higher SSRs were not confined to urban areas, indicating that simple urban–rural differences do not fully explain the observed patterns. Instead, region‐specific healthcare capacity, institutional practices, and referral patterns are likely to contribute to persistent geographic heterogeneity in surgical delivery across prefectures. A marked nationwide shift toward laparoscopic approaches was observed over the study period, with laparoscopic repair increasing steadily even during the COVID‐19‐affected years. This finding indicates widespread adoption of minimally invasive techniques. Age‐ and sex‐specific analyses revealed distinct and reproducible patterns. In males, laparoscopic surgery rates increased uniformly across age groups, suggesting broad dissemination of laparoscopic repair. In females, although laparoscopic use also increased overall, the rate of increase was smaller among women of reproductive age. This pattern may reflect sex‐specific clinical considerations, including inguinal endometriosis or canal of Nuck cysts and preferences for open non‐mesh repair [ 19 ]. Despite the nationwide upward trend, persistent prefecture‐level variation in laparoscopic repair rates was observed. The stability of regional ranking suggests that institutional and regional factors influence the uptake of laparoscopic techniques beyond patient characteristics. Previous workforce studies have also reported maldistribution of physicians in Japan, including anesthesiologists, which may further contribute to regional differences in surgical capacity [ 20 ]. The age‐specific and geographic patterns observed in this study suggest that the adoption of outpatient groin hernia repair is influenced by both patient‐related and healthcare system‐related factors. Outpatient surgery was more common among young and middle‐aged adults, whereas marked prefectural variation and its temporal expansion likely reflect differences in regional healthcare infrastructure, including the availability and diffusion of specialized day‐surgery centers. Importantly, because outpatient surgery in the NDB is defined by reimbursement categories, these patterns do not represent all clinically performed day surgeries. Indeed, even in prefectures with a recorded outpatient surgery rate of 0%, clinically performed day surgery has been confirmed (personal communication), underscoring the influence of reimbursement practices on observed values. Nevertheless, comparison with the National Clinical Database data shows that overall outpatient surgery proportions are not markedly different between the two sources (e.g., 6.9% vs. 5.8% in 2023) [ 21 ], suggesting that this limitation has a limited impact on the broad characterization of regional variation. Moreover, because such misclassification is unlikely to differ systematically by age, the observed age‐specific patterns are considered robust. Together, these findings indicate that the expansion of outpatient groin hernia surgery in Japan reflects the combined effects of patient demand and region‐specific healthcare systems, resulting in persistent geographic heterogeneity [ 22 ]. Nationwide Japanese registry data indicate that emergency groin hernia repairs account for approximately 4%–6% of all procedures [ 8 , 21 ], and previous registry studies suggest that patients undergoing emergency groin hernia surgery tend to be older [ 23 , 24 ]. In the present analysis, population‐based manual reduction rates increased with advancing age in both sexes. Because manual reduction in the NDB is identified through administrative claims rather than detailed clinical information, the recorded data may partly reflect differences in institutional claiming practices in addition to clinical indication. These data should therefore be interpreted as a lower bound indicator of emergency hernia care rather than a direct measure of incarceration incidence. Although the MRI also increased in older age groups, particularly among elderly females, this index may partly reflect changes in surgical volume in the denominator. However, the concurrent age‐related increase observed in population‐based rates indicates that the elevation in MRI cannot be explained solely by a denominator effect, supporting an age‐associated increase in manual reduction procedures. The estimated lifetime manual reduction burden after adulthood should therefore be interpreted as a minimum estimate of cumulative healthcare utilization rather than a measure of individual incarceration risk. At the prefectural level, population‐based manual reduction rates exhibited persistent geographic variation that remained stable across calendar years. This temporal consistency makes it unlikely that the observed regional differences primarily reflect true variation in hernia incidence, acute incarceration risk, underlying emergency care capacity, or differences in population aging structure, such as higher proportions of elderly residents in rural prefectures. Instead, these patterns are more plausibly attributable to regional differences in procedural recognition and reimbursement practices, reflecting institution‐ or region‐specific coding behaviors rather than systematic differences in clinical need. While absolute prefectural rates may therefore be subject to substantial measurement error, the consistent age‐ and sex‐specific patterns observed across regions remain informative and clinically meaningful. This study has several limitations inherent to the use of nationwide administrative claims data. Because the database lacks detailed clinical information and does not allow longitudinal linkage at the individual level, analyses were performed at the procedure level, precluding direct assessment of recurrence or causal inference. Accordingly, measures such as lifetime surgical burden should be interpreted as indicators of cumulative population‐level healthcare utilization rather than individual lifetime risk. Several outcomes were influenced by reimbursement‐based classifications. Outpatient surgery in the NDB is defined by billing categories rather than clinical practice, and same‐day procedures may be classified differently depending on reimbursement rules. Manual reduction procedures may also be underreported or inconsistently captured because of institutional claiming practices, unreimbursed procedures, and omission of cases treated by immediate emergency surgery; therefore, these measures should be interpreted as descriptive indicators rather than direct estimates of incarceration incidence. In addition, misclassification related to hernia type and procedure counting should be considered. Combined inguinal and femoral hernias may be differentially claimed depending on surgical approach, potentially leading to underestimation of femoral hernia procedures, and bilateral repairs may be counted asymmetrically between open and laparoscopic surgery. Finally, prefecture‐level analyses are ecological in nature, and the findings may reflect regional differences in healthcare systems and reimbursement practices rather than true differences in disease incidence.

In conclusion, this nationwide claims‐based analysis demonstrated marked age‐ and sex‐specific patterns in groin hernia surgery in Japan, with a substantially higher cumulative surgical burden in males. Distinct age‐dependent trends in laparoscopic and outpatient surgery reflected evolving surgical practice and region‐specific clinical implementation. Manual reduction activity, despite procedural and reimbursement‐related limitations, served as a meaningful lower bound indicator of emergency‐related healthcare utilization in older populations.

Groin hernia repair is one of the most common surgical procedures worldwide and constitutes a substantial component of routine surgical care [ 1 , 2 ]. In Japan, rapid population aging and ongoing changes in surgical practice, including the widespread adoption of laparoscopic techniques and the expansion of outpatient surgery, are expected to have a significant impact on both the volume and structure of groin hernia care. Despite its importance, comprehensive nationwide analyses capturing longitudinal changes in care delivery remain limited. Administrative claims data provide a robust framework for population‐level evaluation of surgical activity. The National Database of Health Insurance Claims and Specific Health Checkups of Japan (NDB) provides publicly available open data stratified by age, sex, prefecture, hernia type, and surgical approach, as well as procedure‐specific claims such as manual reduction [ 3 , 4 , 5 , 6 , 7 ]. In contrast to registry‐based summaries, which primarily report aggregate surgical volumes [ 8 ], the pre‐stratified structure of the NDB open data enables standardized analyses of age‐ and region‐specific patterns at the national level [ 9 ]. The aim of this study was to provide a nationwide overview of groin hernia management, focusing on surgical rates and longitudinal trends in laparoscopic repair, outpatient surgery, and manual reduction.

K.M. received honoraria from Becton, Dickinson and Company, unrelated to the present manuscript. M.S., T.T., I.N., T.M., S.P., T.H., and H.W. declared no conflicts of interest.

Table S1: Nationwide annual counts of groin hernia surgeries by hernia type and surgical approach in Japan (2014–2023). Table S2: Age‐ and sex‐specific rates of inguinal hernia surgery per 100 000 population by fiscal year in Japan (2014–2023). Table S3: Age‐ and sex‐specific rates of femoral hernia surgery per 100 000 population by fiscal year in Japan (2014–2023). Table S4: Prefecture‐level standardized surgery ratios (SSRs) for groin hernia surgery by fiscal year in Japan (2014–2023). Table S5: Age‐ and sex‐specific rates of laparoscopic surgery rate by fiscal year in Japan (2014–2023). Table S6: Prefecture‐level laparoscopic repair rates for groin hernia surgery in Japan by fiscal year (2014–2023). Table S7: Age‐specific rates of outpatient surgery rate by fiscal year in Japan (2015–2023). Table S8: Prefecture‐level outpatient surgery rate in Japan by fiscal year (2014–2023). Table S9: Age‐ and sex‐specific manual reduction per 100 000 population by fiscal year in Japan (2014–2023). Table S10: Age‐ and sex‐specific manual reduction index by fiscal year in Japan (2014–2023). Table S11: Prefecture‐level manual reduction per 100 000 population by fiscal year in Japan (2014–2023).