Japan's Nationwide Trend in Scoliosis Surgery from 2014 to 2022; from a Country with a Declining Underage Population

Abstract

Introduction

Japan is experiencing a significant demographic shift characterized by a declining birthrate and an aging population. A previous report indicated a discrepancy between the trends in the number of spinal surgeries performed for minors and the overall population dynamics. Japan has the National Database of Health Insurance Claims and Specific Health Checkups (NDB), which contains 99.9% of public health insurance claims from hospitals and 97.9% from clinics. This study aimed to investigate the annual number of scoliosis surgeries performed on patients aged 19 years in Japan, evaluate trends in relation to the overall population dynamics, and examine potential factors contributing to the observed changes.

Methods

This retrospective study utilized NDB and census data. Scoliosis surgeries were identified using K-codes specific to the procedure. Population data were estimated using census and national birth records released by the Japan Cabinet Office. The number of surgeries per 100,000 minors was calculated, and trends were analyzed from 2014 to 2021.

Results

The number of scoliosis surgeries for patients under 19 years old increased from 1,282 in 2014 to 1,850 in 2021, despite a decrease in the number of patients under 19 years old. The rate of scoliosis surgeries per 100,000 minors increased from 5.6 in 2014 to 9.1 in 2021, whereas other spinal fusion procedures for minors did not show significant changes during the same period.

Conclusions

Despite a decline in the underage population, the number of scoliosis surgeries among minors has paradoxically increased in Japan. Improvements in screening tools and the April 2016 change in the law mandating a full motor examination, including scoliosis testing, may have affected this trend. Further follow-up studies are required.

Introduction

Japan is currently experiencing a significant demographic shift characterized by a rapidly declining birth rate and an aging population¹⁾. This trend is not unique to Japan²⁾; other developed countries, such as Italy, Germany, and South Korea, are also facing similar demographic challenges^1,3). However, Japan has a low immigration rate of only 1.5%-2.4%^4,5), which may exaggerate the country's population decline. This demographic trend poses various challenges across multiple sectors, including healthcare. The decreasing number of minors raises pertinent questions about the demand for pediatric medical services, including surgical interventions.

Scoliosis, a condition involving abnormal lateral curvature of the spine, may occur during adolescence⁶⁾. Surgical treatment for scoliosis is often recommended for severe cases to prevent progression and improve quality of life⁶⁾. If there is no change in the prevalence of scoliosis or the indications for surgery, scoliosis surgery in Japan should decline, given the recent rapid decline in the population under the age of 19. Despite the decreasing number of minors, anecdotal evidence and preliminary observations indicate a paradoxical trend: an increase in spine surgeries in patients under 19 years old⁷⁾. However, a previous study did not provide detailed data about scoliosis-associated surgery⁷⁾. In addition, it has not been evaluated how the April 2016 change in the law requiring a full musculoskeletal examination, including scoliosis testing, on scoliosis surgery in minors has not been evaluated.

In the context of the changing demographics of Japan, providing a comprehensive epidemiological overview of scoliosis surgery is important. The purpose of this study was to rigorously investigate the annual number of scoliosis surgeries performed on patients aged 19 years and younger in Japan, along with the demographics of the population from the fiscal year 2014 to 2022.

Materials and Methods

NDB files

Given the universal insurance coverage in Japan, facilitated by the National Database of Health Insurance Claims and Specific Health Checkups of Japan (NDB), the country maintains comprehensive records of healthcare services⁷⁾. The NDB encompasses 99.9% of public health insurance claims from hospitals and 97.9% from clinics, providing a robust dataset for analyzing healthcare trends⁸⁾. Since 2014, the Ministry of Health, Labor, and Welfare (MHLW) has released data from the NDB⁹⁾. The MHLW released data on the number of surgeries from 2014 to 2022 fiscal year on their website⁹⁾. Since the Japanese fiscal year begins in April 1 and ends in March 31 each year, these data cover the period from April 2014 to March 2023. We downloaded an age, sex, or region-based Excel^Ⓒ file per fiscal year. Using these files, we were able to investigate the type of spinal surgery performed and the sex and age of the patients. Age data were expressed by the 5-year category (0-4 years old, 5-9 years old, 10-14 years old, 15-19 years old, >20 years old). If there were fewer than 10 cases in one category, these files were expressed as “−” instead of the actual number of cases to protect personal information, which is a Japan-specific rule established by the MHLW⁷⁾.

Analyses using K-code

We performed the K-code-based survey; a K-code is a unique procedure classification set by the MHLW in Japan^7,10). In this study, we investigated K142-2 (scoliosis surgery), including scoliosis fusion surgery, primary instrumentation surgery for scoliosis correction, instrumentation exchange surgery for scoliosis, and rod extension surgery for scoliosis. The number of scoliosis surgeries performed on patients aged 19 years and younger as well as those over 20 years of age (as a reference) was calculated. As another reference data, we surveyed the number of spinal instrumentation procedures performed on minors each year using K-code 142, which includes anterior fusion, posterior lateral fusion, and posterior fusion, whose diagnostic codes were 150282510, 15282610, and 150314610, respectively. This is because spondylolisthesis is an indication for spinal fusion, even among minors¹¹⁾. Although day surgeries without admission were excluded from the admission database, the number of scoliosis spine surgeries performed without hospitalization was likely minimal⁷⁾. Hence, only inpatient data were used in this study.

Estimation of the underage population

Considering the low immigration rate^4,5) and child mortality rate¹²⁾ in Japan, we estimated the number of populations under 19 years of age using the following two methods. The first approach used census data¹³⁾. In Japan, an official census is conducted every 5 years, and the data are used to produce preliminary figures for each age group each year. In this study, we used the age/sex-based population Excel^Ⓒ file showing the population as of 2022 for each age group produced by the Statistics Bureau of Japan¹³⁾. To verify an underage population as indicated by the census, the second method used the Number of Births data introduced by the Cabinet Office of Japan¹⁴⁾. The age of minors (0-19) in each fiscal year from 2014 to 2022 was calculated from the number of births per year.

Number of surgeries calculated for each population and month

After confirming that there was no difference between the census-based and birth data for the Japanese minor population, we calculated the number of scoliosis surgeries for every 100,000 minors in the census data for the years 2014-2022. As a reference, the rate of other spine surgeries per 100,000 minors was also calculated. Additionally, to assess the impact of the declaration of a state of emergency related to COVID-19 and the monthly trends in scoliosis surgery, we examined the number of primary scoliosis surgeries per month. Since these data were provided after 2019, 4 years were examined.

To assess the regional distribution of primary scoliosis surgeries, we evaluated the population and the number of surgeries in 10 blocks (Hokkaido, Tohoku, South Kanto, North Kanto and Koshin, Hokuriku, Tokai, Kinki, Chugoku, Shikoku, and Kyushu areas). Subsequently, we calculated the number of primary scoliosis surgeries per 100,000 population based on the NDB showing the number of surgeries per prefecture. This NDB file excludes age data; hence, the number of surgeries is assessed for all ages in each population. This was examined in the 2015 and 2022 data because regional data were not produced for the 2014 fiscal year.

Results

Trends in the total number of scoliosis-associated spine surgeries from 2014 to 2022 in Japan

The number of scoliosis surgeries for patients aged 19 years and younger almost steadily increased from 1282 in 2014 to 1850 in 2021, with the exception of a slight decrease in 2020 (Table 1). In 2022, its number decreased to 1746. After excluding rod extensions and exchange surgeries, the trend was similar. From 2014 to 2022, there was no significant change in the number of scoliosis procedures for patients older than 20 years and other spinal fusion procedures for patients younger than 19 years.

Table 1.

Number of Surgeries per Fiscal Year in Japan.

	Fiscal Year
Surgery type	2014	2015	2016	2017	2018	2019	2020	2021	2022
Scoliosis surgery for patients ≤19 years old	1282	1408	1399	1551	1652	1827	1635	1850	1746
Scoliosis surgery for patients ≤19 years old excluding rod extension or exchange surgery	844	936	948	1126	1247	1389	1264	1524	1434
Scoliosis surgery for patients ≥20 years old	793	769	779	862	969	803	735	795	760
Other spinal fusion procedures for patients ≤19 years old	380	348	358	357	351	434	358	337	326

Japan's underage population from 2014 to 2022

Table 2 presents the population by age group in Japan (in thousands). The difference in the population aged under 19 years from the two sets of data was within 3% each year. Japan's population under the age of 19 has declined by 11.1% on a census basis and by 8.8% on the basis of fertility-derived data over the past 7 years.

Table 2.

Population in Japan of Each Age Group (by the Thousands).

		Census based population					Birth data based population
	Age	total	(%)	male	female		total	(%)	male	female
2014	0-19	22,979	reference	11,792	11,187		22,314	reference	11,451	10,863
	0-9	10,571		5,419	5.153		10,599		6,007	5,702
	10-14	5,984		3,076	2,909		5,749		2,383	2,256
	15-19	6,424		3,297	3,125		5,966		3,061	2,905
2015	0-19	22,686	98.7	11,640	11,047		22,133	99.2	11,358	10,775
	0-9	10,666		5,467	5,200		10,542		5,953	5,651
	10-14	5,629		2,892	2,738		5,621		2,340	2,219
	15-19	6,391		3,281	3,109		5,970		3,065	2,905
2016	0-19	22,380	97.4	11,482	10,900		21,904	98.2	11,241	10,663
	0-9	10,401		5,331	5,072		10,427		5,911	5,608
	10-14	5,629		2,892	2,738		5,543		2,284	2,167
	15-19	6,350		3,259	3,090		5,934		3,046	2,888
2017	0-19	22,031	95.9	11,302	10,732		21,658	97.1	11,114	10,544
	0-9	10,255		5,255	5,002		10,283		5,834	5,538
	10-14	5,512		2,830	2,682		5,479		2,252	2,138
	15-19	6,264		3,217	3,048		5,896		3,028	2,868
2018	0-19	21,656	94.2	11,108	10,551		21,374	95.8	10,968	10,406
	0-9	10,081		5,165	4,918		10,111		5,746	5,456
	10-14	5,453		2,797	2,656		5,447		2,235	2,121
	15-19	6,122		3,146	2,977		5,816		2,987	2,829
2019	0-19	21,261	92.5	10,905	10,359		21,061	94.4	10,806	10,255
	0-9	9,883		5,063	4,822		9,906		5,629	5,347
	10-14	5,394		2,766	2,628		5,406		2,225	2,111
	15-19	5,984		3,076	2,909		5,749		2,952	2,797
2020	0-19	20,832	90.7	10,682	10,153		20,711	92.8	10,625	10,087
	0-9	9,654		4,944	4,711		9,675		5,511	5,236
	10-14	5,381		2,759	2,623		5,415		2,229	2,115
	15-19	5,797		2,979	2,819		5,621		2,885	2,736
2021	0-19	20,417	88.9	10,468	9,952		20,352	91.2	10,440	9,913
	0-9	9,427		4,827	4,601		9,436		5,376	5,111
	10-14	5,361		2,749	2,613		5,373		2,219	2,103
	15-19	5,629		2,892	2,738		5,543		2,845	2,699
2022	0-19	20,014	87.1	10,259	9,757		19,969	89.5	10,242	9,727
	0-9	9,195		4,709	4,487		9,169		5,233	4,973
	10-14	5,307		2,720	2,588		5,321		2,197	2,086
	15-19	5,512		2,830	2,682		5,479		2,812	2,668

Trends in the number of scoliosis procedures per population by year and region

The number of scoliosis surgeries per 100,000 minors increased from 5.6 in 2014 to 9.1 in 2021, excluding a slight decrease from the previous year in 2020 and 2022 (Fig. 1). The number of spinal fusion procedures performed for minors did not significantly change from 1.5 per 100,000 in 2014 to 1.6 per 100,000 in 2022. Monthly data including all ages showed that there were more primary scoliosis surgeries in July, August, January, and March, which corresponded to Japanese school summer/winter/spring vacations (Fig. 2). There was a decrease in the number of primary scoliosis surgeries in May 2020, which was during the first declaration of a State of Emergency for COVID-19.

Figure 1.

The number of surgeries for scoliosis and other spinal fusions per 100,000 minors in Japan.

Figure 2.

Monthly data on the number of scoliosis primary surgeries, including all ages from April 2019 to March 2022.

West Japan tends to have fewer primary scoliosis surgeries per 100,000 people than east Japan (Fig. 3). The number of primary scoliosis surgeries per 100,000 population more than tripled between regions in 2015 (3.2 times; 2.307 in North Kanto/Koshin and 0.728 in Shikoku) and in 2022 (3.3 times; 2.380 in Hokuriku and 0.718 in Shikoku). Compared with 2015, the number of surgeries per population increased in all areas except for North Kanto/Koshin (from 2.307 to 1.634) and Shikoku in 2022 (from 0.728 to 0.718).

Figure 3.

Regional differences in the number of primary scoliosis surgeries between 2015 (a) and 2022 (b).

Discussion

The rapidly declining birthrate is not just a Japanese problem, as this is a demographic challenge^1,3). Although understanding the number of surgeries performed nationwide is fundamental to the epidemiology of various surgical procedures⁷⁾, spine surgery for patients aged 19 years and younger has not yet been well studied. This study explored the paradoxical trend of increasing scoliosis surgery numbers in Japan despite the country's declining underage population. Our findings revealed an increasing trend in the number of scoliosis surgeries performed on patients younger than 19 years from 2014 to 2021, increasing from 1,282 to 1,850 procedures, although there were slight decreases in the number of surgeries in 2020 compared with the previous year. Previous studies have shown that the decrease in the number of surgeries in 2020 was due to the COVID-19 pandemic^7,15). This trend persists even when excluding rod extension or exchange surgeries, suggesting a genuine increase in primary scoliosis surgeries rather than an artifact of follow-up procedures.

Our results contrast with expected trends in demographic shifts. The steady increase in the number of scoliosis surgeries observed in our study contradicts the general expectation that medical interventions for minors would decrease in line with the declining birthrate and aging population^1,3). Previous studies have not provided detailed data on scoliosis-related surgeries in Japan, and our findings address this gap by presenting a comprehensive analysis using robust national data⁷⁾. This discrepancy highlights the importance of investigating specific medical trends within broader demographic contexts. Several factors may explain the observed increase in scoliosis surgery among minors. Advances in surgical techniques and better detection and diagnosis of scoliosis could contribute to the rise in surgeries¹⁶⁾.

In Japan, a legal amendment in April 2016 made motor testing, including scoliosis testing, fully mandatory, creating a system for comprehensive testing of children's entire motor system¹⁷⁾. This change may have triggered potential surgical demand and contributed to an increase in the number of scoliosis surgeries through 2021. Enhanced awareness and screening programs might lead to more diagnoses and, consequently, more surgical interventions, following the increasing number of studies on adolescent idiopathic scoliosis (AIS)^16,18). However, long-term comparative observational studies are inherently necessary to determine the effectiveness of the screening system change. This is because the widespread use of screening may have the contradictory effect of reducing the number of surgeries associated with orthotic treatment. However, it may also increase the number of patients with potential scoliosis, thereby increasing the number of surgeries. There are regional differences in the number of school boards that have introduced the use of testing equipment, although this does not cover the whole of Japan¹⁹⁾. Okuwaki et al. argued that patients with AIS referred from municipalities that performed only screening testing had greater scoliosis at the initial visit than those referred from municipalities that performed exercise testing and objective testing²⁰⁾. In 2022, the number of scoliosis surgeries decreased from the previous year, indicating that the declining birth rate may finally have an impact, and further investigation is needed.

The demographic trend of a declining young population is not unique to Japan. For instance, underage population rates are similarly low in other developed countries: South Korea (11.2%), Japan (11.3%), Italy (12.2%), Spain (13.5%), and Germany (14.0%)²¹⁾. Even in the U.S., the birth rate consistently decreased by 2% annually, reaching 1.66 in 2022²²⁾. This widespread demographic shift raises the question of whether the observed increase in scoliosis surgeries is specific to Japan or if similar trends might occur in other countries with declining youth populations. However, collecting nationwide data on the number of surgeries poses significant challenges, even in the US²³⁾ and Germany²⁴⁾ because of the healthcare system's complexity, which involves private insurance. These challenges highlight the value of Japan's comprehensive NDB, which provides an opportunity to analyze national healthcare trends.

Our findings also have meaningful implications for healthcare planning and resource allocation in Japan¹⁷⁾. We were able to identify regional differences in scoliosis surgery at all ages, not just at an early age. However, it is noteworthy that the regional differences in the number of scoliosis surgeries per population were three times greater than the regional differences in the number of scoliosis surgeries per population. The pre- and postoperative management of scoliosis requires the cooperation of pediatricians, and regional differences in pediatric specialty care facilities be considered. This study showed that the Shikoku region had the lowest ratio of scoliosis procedures to population. This finding may have been influenced by the fact that Shikoku only has one pediatric specialty facility, excluding university hospitals. However, the data presented in Fig. 3 included scoliosis in all age groups. The orthopedic specialty of each university may also influence the surgical treatment of scoliosis, which requires multidisciplinary care. Despite the decreasing number of minors, the increasing demand for scoliosis surgery may indicate the need for sustained or even enhanced capacity in pediatric orthopedic services. Early-onset scoliosis is associated with reduced life expectancy⁶⁾, but surgery for AIS that develops after the age of 10 years has an unaltered prognosis for life²⁵⁾. Hence, the indications for surgery should not be excessive. Research on treatments to avoid surgery for scoliosis has also been conducted in recent years²⁶⁾. Policymakers and healthcare providers should consider these trends when planning for future healthcare infrastructure and workforce needs.

This study has several limitations. First, the use of aggregated data from the NDB means that we cannot account for individual patient factors that might influence surgery rates, such as disease severity and comorbidities. In particular, NDB cannot distinguish between AIS and early-onset scoliosis. Second, categorizing age groups into 5-year intervals may mask more nuanced trends within specific age ranges. Third, the data suppression rule for categories with fewer than 10 cases might lead to underreporting in some cases, although this is unlikely to significantly impact the overall trend. Fourth, this research excluded mandatory vehicle liability insurance and workers' compensation-related surgeries. However, these effects were minimal considering the pathophysiology of scoliosis. Future research should investigate the reasons for the increase in the number of scoliosis surgeries despite the declining proportion of patients, focusing on surgical advancements, clinical guidelines, and early detection programs. Longitudinal studies that track patient outcomes and surgical decisions are beneficial. Comparative studies with other countries facing similar demographic shifts but with different healthcare systems could provide broader insights, helping to inform global healthcare strategies for managing scoliosis and other pediatric conditions.

In conclusion, this study highlights a paradoxical increase in the number of scoliosis surgeries among minors in Japan, despite the declining underage population. The findings underscore the need for ongoing monitoring and analysis of healthcare trends in specific demographic contexts.

Conflicts of Interest: The authors declare that there are no relevant conflicts of interest.

Sources of Funding: None.

Author Contributions: K.N. designed the research and wrote the manuscript. M.N. analyzed the data and supervised the study. All authors have reviewed the manuscript.

Ethical Approval: This study was performed using publicly available data.

Informed Consent: NA