Nationwide Trends and Safety Analysis of Adult Spinal Instrumentation Surgery: A Study using the JSIS-DB

Abstract

Introduction

Spinal instrumentation surgery is increasingly being performed in aging populations; however, comprehensive data regarding the nationwide trends and perioperative safety associated with these procedures in Japan remain limited. This study aimed to evaluate the epidemiological characteristics and complication profiles of adult spinal instrumentation surgery using the Japanese Spinal Instrumentation Society Database (JSIS-DB).

Methods

A retrospective observational study was conducted using JSIS-DB data from 2018 to 2022. Adults aged ≥18 years who underwent spinal surgeries involving instrumentation across intervertebral levels were included. Data for demographic characteristics, diagnosis, surgical procedure, operative time, blood loss, and complications within 14 days of surgery were analyzed. The primary outcome was the overall perioperative complication rate, whereas the secondary outcomes included complication rates stratified by age and pathology.

Results

A total of 28,832 cases were analyzed (mean age: 67.3±14.4 years; males: 48.7%). The most common diagnosis was degenerative disease (62.9%), followed by spinal deformity (15.4%), trauma (15.2%), tumors (3.5%), and infection (2.6%). The most frequently performed procedure was posterior lumbar interbody fusion (40.8%), followed by posterior or posterolateral fusion (32.6%). The overall complication rate was 11.0%. The specific complication rates were as follows: dural tears, 2.5%; nerve root disorders, 1.4%; epidural hematomas, 1.1%; surgical-site infections, 0.8%; spinal cord disorders, 0.4%; and mortality, 0.1%. Patients aged ≥90 years showed a significantly higher complication rate (18.6%, p<0.001). The complication rates by pathology were as follows: deformities, 13.9%; infections, 13.4%; tumors, 13.3%; trauma, 12.3%; and degenerative diseases, 9.8% (p<0.001).

Conclusions

This nationwide registry-based study successfully visualized the real-world practices and risk profiles of adult spinal instrumentation surgery in Japan. Elderly patients and those with deformities, infections, or tumors showed significantly higher perioperative risks, highlighting the need for enhanced preoperative assessments and perioperative care. These findings provide foundational data to improve the safety and quality of spinal surgery.

Introduction

Japan has become a super-aged society, resulting in a rapid increase in spinal degenerative diseases that substantially impair individuals' quality of life¹⁾. Although many of these conditions can be managed using conservative approaches, surgical intervention is often required in cases showing progressive instability or neurological deficits^2,3). Spinal instrumentation surgery is indispensable for restoring stability; however, it involves costly implants and is associated with a high risk of complications^4,5). According to the 2011 Nationwide Survey of Spine Surgery, instrumentation procedures accounted for 30.2% of all spine surgeries⁶⁾. However, these procedures involve expensive implants that impose a substantial economic burden on the healthcare system⁷⁾. Moreover, while this nationwide survey reported an overall complication rate of 10.4% for all spine surgeries, the complication rate for instrumentation surgeries was higher (15.6%)⁶⁾. These findings underscore the need for detailed nationwide analyses to identify the risk factors in instrumentation surgeries and improve surgical safety. In many European countries, national spine surgery registries have been successfully implemented, contributing to quality improvement, complication reduction, and evidence-based decision-making in clinical practice^8-12). Registry-based analyses can not only provide insights into real-world surgical outcomes but also facilitate the development of safer surgical techniques and innovative medical devices. The Japanese Spinal Instrumentation Society (JSIS) launched a web-based multicenter prospective registry (JSIS Database, JSIS-DB) in 2018¹³⁾. This initiative aimed to systematically collect detailed perioperative data, enabling comprehensive nationwide analyses of trends, patient demographic characteristics, surgical techniques, and complication profiles. In this study, we analyzed data from the JSIS-DB to elucidate nationwide trends and evaluate the safety profile of adult spinal instrumentation surgery in Japan.

Materials and Methods

Study design and ethical considerations

This retrospective observational study of adult patients (≥18 years) registered in the JSIS-DB between February 2018 and March 2022 included all spinal surgeries in which instrumentation was used for fixation or stabilization across intervertebral segments. The primary outcome was the incidence of perioperative complications. Secondary outcomes included the distribution of cases and complication rates in relation to the age group and primary diagnosis.

The study was conducted in accordance with the Declaration of Helsinki. Informed consent for participation in the registry was obtained from all patients or their legal representatives, and an opt-out process approved by the ethics committee was implemented in cases in which written consent could not be obtained. The use of the JSIS-DB data for secondary research was reviewed and approved by the ethics committee of the relevant academic society.

To ensure data reliability, the JSIS-DB data-cleansing team, which consisted of multiple certified spine surgeons and administrative staff, reviewed the data stored in the JSIS-DB. After checking questionable cases, the JSIS-DB secretariats provided feedback and requested corrections.

Data collection and surgical information

The data registered in the JSIS-DB included information regarding patient demographic characteristics (age, sex, height, and weight) and surgical information such as operative time, intraoperative blood loss, surgical classification (elective or emergency), operation type (initial surgery, staged surgery, or revision/additional surgery), primary diagnosis, presence of Parkinson disease, preoperative neurological status (none, spinal cord involvement, or cauda equina/nerve root involvement), and presence of preoperative bladder or bowel dysfunction. Details of the surgical procedure were recorded, including the number of fused levels, intraoperative supportive technologies used (fluoroscopy, autologous blood salvage, neuromonitoring, navigation, microscopy, or endoscopy), surgeon information (<5, 5-9, 10-14, and ≥15 years of postgraduate experience), bone graft use (none, autograft, allograft, or artificial bone), and type of implant used. To estimate the national coverage of this registry, we referred to publicly available statistics from the National Database of Health Insurance Claims and Specific Health Checkups of Japan (NDB), which is operated by the Ministry of Health, Labour and Welfare¹⁴⁾. The NDB provides nationwide counts of medical procedures on the basis of insurance claims data. Using these data, we calculated the proportion of adult spinal instrumentation surgeries registered in the JSIS-DB relative to the total number of spinal fusion procedures performed nationwide during the corresponding period.

Intraoperative and postoperative complications

Complications, including intraoperative events and postoperative complications occurring within 14 days after surgery, were documented in all cases. Complication categories are summarized in Supplementary Table 1.

Statistical analyses

Differences in complication rates across the diagnostic categories were assessed using the chi-square test. When significant overall differences were detected, pairwise comparisons were performed using Fisher's exact test. To adjust for multiple comparisons, the Bonferroni correction was applied. Statistical significance was set at p<0.05. Statistical analyses were conducted using IBM SPSS Statistics (version 30.0; IBM Corp., Armonk, NY, USA).

Results

Patient demographic characteristics

A total of 32,656 patients from 124 institutions were registered in the JSIS-DB during the study period. Of these, 28,832 adult patients (age ≥18 years) who underwent spinal instrumentation surgery were included in this study. According to the NDB, this cohort accounted for approximately 10.4% of all spinal fusion procedures performed nationwide during the corresponding period between February 2018 and March 2022. The mean patient age was 67.3 years (range, 18-98 years). The most common age group was 70-79 years (10,739 patients, 37.2%) (Figure 1). The cohort included 14,047 males (48.7%) and 14,785 females (51.3%). The mean patient height was 158.1±10.2 cm, and the mean body weight was 60.2±13.8 kg. The mean postoperative stay was 26.1±24.9 days, and 7,026 patients (24.4%) were discharged within 14 days after surgery.

Figure 1.

Age distribution of adult patients undergoing spinal instrumentation surgery (n=28,832). The most common age group was 70-79 years (10,739 patients, 37.2%), followed by 60-69 years (7,090 patients, 24.6%) and 80-89 years (4,755 patients, 16.5%). The mean patient age was 67.3 years (range: 18-98 years), reflecting the predominance of elderly patients undergoing contemporary spinal surgery in Japan.

Surgical characteristics

The mean operative time was 198.4±102.7 min, and the mean intraoperative blood loss was 298.0±350.0 mL (Table 1). Elective and emergency surgeries accounted for 27,202 (94.3%) and 1,630 (5.7%) cases, respectively. Initial, staged, and revision or additional surgeries accounted for 23,532 (81.6%), 1,746 (6.1%), and 3,554 (12.3%) cases, respectively. Of all procedures, 1.0%, 11.0%, 14.3%, and 73.7% were performed by surgeons with <5 years, 5-9 years, 10-14 years, and ≥15 years of experience, respectively.

Table 1.

Surgical Characteristics.

Variable	Mean±SD or n (%)
Operative time (min)	198.4±102.7
Intraoperative blood loss (mL)	298.0±350.0
Postoperative length of stay (days)	26.1±24.9
Surgical classification
Elective surgery	27,202 (94.3)
Emergency surgery	1,630 (5.7)
Operation type
Initial surgery	23,532 (81.6)
Staged surgery	1,746 (6.1)
Revision/additional surgery	3,554 (12.3)
Surgeon experience (years)
<5	281 (1.0)
5-9	3,182 (11.0)
10-14	4,119 (14.3)
≥15	21,250 (73.7)

SD: standard deviation

Diagnosis and preoperative neurological status

The most common diagnostic category was degenerative disease, accounting for 18,132 cases (62.9%), followed by deformity (4,451 cases, 15.4%), trauma (4,369 cases, 15.2%), tumors (1,006 cases, 3.5%), infection (749 cases, 2.6%), and other conditions (125 cases, 0.4%) (Table 2). The most frequent specific diagnosis was lumbar spinal stenosis (7,302 cases, 25.3%), followed by lumbar spondylolisthesis (4,560 cases, 15.8%) (Table 2). In the preoperative assessments of neurological status, no deficit was present in 7,506 cases (26.0%); spinal cord disorder was reported in 5,428 cases (18.8%); and cauda equina or nerve root disorder was identified in 16,241 cases (56.3%). Bladder or bowel dysfunction was absent in 25,333 cases (87.9%), present without retention in 2,503 cases (8.7%), and present with confirmed or suspected retention in 996 cases (3.5%).

Table 2.

Diagnosis and Preoperative Neurological Status.

Category/variable	n (%)
Primary diagnosis category
Degenerative	18,132 (62.9)
Deformity	4,451 (15.4)
Trauma	4,369 (15.2)
Tumor	1,006 (3.5)
Infection	749 (2.6)
Other	125 (0.4)
Specific diagnosis (top 10)
Lumbar spinal stenosis	7,302 (25.3)
Lumbar spondylolisthesis	4,560 (15.8)
Degenerative scoliosis	1,527 (5.3)
Lumbar fracture	1,362 (4.7)
Degenerative kyphosis	1,326 (4.6)
Lumbar disc herniation	1,276 (4.4)
Cervical spondylotic myelopathy	1,168 (4.1)
Cervical disc herniation	591 (2.0)
Cervical ossification posterior longitudinal ligament	492 (1.7)
Degenerative kyphoscoliosis	461 (1.6)
Preoperative neurological status
None	7,506 (26.0)
Spinal cord disorder	5,428 (18.8)
Cauda equina/nerve root disorder	16,241 (56.3)
Preoperative bladder/bowel dysfunction
None	25,333 (87.9)
Present – without urinary retention	2,503 (8.7)
Present – with urinary retention	996 (3.5)

Surgical procedures and implants

The most common primary surgical procedure was posterior interbody fusion, which was performed in 11,774 cases (40.8%), followed by posterior or posterolateral fusion in 9,409 cases (32.6%) (Table 3). Fluoroscopy was the most frequently used modality (17,221 cases; 59.7%), followed by neuromonitoring (12,918 cases; 44.8%) (Table 3). Autografts were most frequently used for bone grafting (22,396 cases; 77.7%), followed by artificial bone (8,114 cases; 28.1%). Screws were used in 24,660 cases (85.5%), followed by rods in 23,874 cases (82.8%) (Table 3). Single-level fusion was the most common procedure (11,731 cases; 40.7%), followed by two-level fusion (5,570 cases; 19.3%) (Table 3). Overall, short fusions involving 1-2 levels accounted for 60.0% of the cases, whereas long fusions involving ≥7 levels were performed in 3,090 cases (10.7%).

Table 3.

Surgical Procedures, Supportive Technologies, Bone Grafting, Implant Usage, and Fusion Levels.

Primary surgical procedures
Category	Item	n (%)
Primary surgical procedures	Posterior lumbar interbody fusion	11,774 (40.8%)
	Posterior or posterolateral fusion	9,409 (32.6%)
	Anterior spinal fusion	3,225 (11.2%)
	Combined anterior–posterior fusion	2,440 (8.5%)
	Scoliosis corrective fusion	1,518 (5.3%)
	Osteotomy	160 (0.6%)
	Tumor-related surgery	94 (0.3%)
	Cervical artificial disc replacement	55 (0.2%)
Intraoperative supportive technologies	Fluoroscopy	17,221 (59.7%)
	Neuromonitoring	12,918 (44.8%)
	Image-guided support	6,189 (21.5%)
	Navigation	5,688 (19.7%)
	Autologous blood salvage	4,832 (16.8%)
	Microscope	1,831 (6.4%)
	Endoscope	33 (0.1%)
Bone grafting	Autograft	22,396 (77.7%)
	Artificial bone	8,114 (28.1%)
	Allograft	2,263 (7.8%)
	None	4,115 (14.3%)
Implant usage	Screws (pedicle, cortical bone trajectory)	24,660 (85.5%)
	Rods	23,874 (82.8%)
	Posterior interbody cage	12,096 (42.0%)
	Transverse fixator	7,112 (24.7%)
	Anterior interbody cage	4,577 (15.9%)
	Plates	1,242 (4.3%)
	Hooks	881 (3.1%)
	Vertebral replacement cage	613 (2.1%)
	Artificial disc	77 (0.3%)
Number of fused levels	1 level	11,740 (40.7%)
	2 levels	5,647 (19.6%)
	3 levels	3,038 (10.5%)
	4 levels	2,495 (8.7%)
	5 levels	1,374 (4.8%)
	6 levels	961 (3.3%)
	7 levels	545 (1.9%)
	8 levels	838 (2.9%)
	9 levels	694 (2.4%)
	10 levels	340 (1.2%)
	11 levels	208 (0.7%)
	12 levels	126 (0.4%)
	13 levels	151 (0.5%)
	14 levels	99 (0.3%)
	15 levels	37 (0.1%)
	16 levels	35 (0.1%)
	17 levels	7 (0.0%)
	18 levels	2 (0.0%)
	19 levels	1 (0.0%)
	20 levels	3 (0.0%)
	21 levels	3 (0.0%)
	22 levels	0 (0.0%)
	23 levels	1 (0.0%)

The distribution of the procedures differed according to the surgeon's experience level (Supplementary Table 2). Surgeons with <5 years of postgraduate experience almost exclusively performed posterior approaches, with posterior/posterolateral fusion and posterior interbody fusion accounting for 49.1% and 46.6% of the procedures performed by these surgeons; this subgroup of surgeons rarely performed anterior and combined anterior-posterior procedures and almost never performed deformity correction or tumor-related surgeries. Among surgeons with 10-14 years of experience, posterior interbody fusion (42.0%) was still the most frequent procedure; however, they performed anterior fusion (10.9%) and combined anterior-posterior procedures (6.9%) more frequently, and they also performed some deformity-related procedures such as scoliosis surgery (fusion) (3.3%). In contrast, surgeons with ≥15 years of experience demonstrated the broadest spectrum of surgical practice; although posterior interbody fusion (40.3%) and posterior/posterolateral fusion (30.0%) remained the most frequent procedures performed by these surgeons, they also performed a higher proportion of anterior fusion (11.9%) and combined anterior-posterior fusion (9.5%) than the less-experienced groups. The mean fused levels tended to be slightly higher in the ≥15-year group than in the other groups (p<0.001). In terms of categorical distributions, short fusions (1-2 levels) were more common among less-experienced surgeons, whereas long fusions (≥7 levels) were more frequently performed by surgeons with ≥15 years of experience (p<0.001). Among surgeons with 10-14 years and ≥15 years of experience, the mean numbers of fused levels were 2.8±2.5 and 3.1±2.8, respectively. The proportions of cases involving deformities, tumors, and infections in these two surgeon groups were, respectively, 8.0% vs. 18.9%, 5.0% vs. 3.1%, and 3.4% vs. 2.3%; the mean operative times in these groups were 193.1±92.4 vs. 201.8±106.3 min, respectively. These findings indicate that the ≥15-year group tended to manage slightly more complex cases, with a higher rate of deformities and longer constructs.

Intraoperative and postoperative complications

Among the 28,832 cases, complications occurred in 3,185 cases, yielding an overall complication rate of 11.0%. The most frequent intraoperative and postoperative complications were dural tears (713 cases, 2.5%), followed by nerve root disorders (404 cases, 1.4%), epidural hematomas (318 cases, 1.1%), implant migration or malpositioning (238 cases, 0.8%), and implant breakage or dislocation (120 cases, 0.4%) (Table 4). The less frequent events included spinal cord disorder (110 cases, 0.4%), dysphagia or airway obstruction (60 cases, 0.2%), cauda equina disorder (46 cases, 0.2%), hemothorax/pneumothorax/chylothorax (37 cases, 0.1%), wrong-level surgery (21 cases, 0.1%), and major-vessel injury (15 cases, 0.05%). Bowel injury (4 cases, 0.0%) and ureteral injury (3 cases, 0.0%) were very rare.

Table 4.

Intraoperative and Postoperative Complications within 14 Days.

Intraoperative and postoperative complications	n (%)
Dural tears	713 (2.5%)
Epidural hematoma	318 (1.1%)
Nerve root disorder	404 (1.4%)
Spinal cord disorder	110 (0.4%)
Cauda equina disorder	46 (0.2%)
Major vessel injury	15 (0.1%)
Surgical site infection	229 (0.8%)
Bowel injury	4 (0.0%)
Ureteral injury	3 (0.0%)
Hemothorax/pneumothorax/chylothorax	37 (0.1%)
Dysphagia or airway obstruction	60 (0.2%)
Implant migration or malposition	238 (0.8%)
Implant breakage or dislocation	120 (0.4%)
Wrong-level surgery	21 (0.1%)
Systemic complications	n (%)
Psychiatric disorders (delirium etc.)	300 (1.0%)
Respiratory complications (pneumonia, atelectasis)	141 (0.5%)
Gastrointestinal complications (ileus, perforation)	110 (0.4%)
Pulmonary embolism/peripheral embolism	97 (0.3%)
Cardiovascular events (heart failure and myocardial infarction)	77 (0.3%)
Cerebral complications (infarction, hemorrhage)	29 (0.1%)
Mortality	27 (0.1%)

Among systemic complications, the most frequent complications were psychiatric disorders such as delirium (300 cases, 1.0%), followed by respiratory complications such as pneumonia or atelectasis (141 cases, 0.5%), gastrointestinal complications such as ileus or perforation (110 cases, 0.4%), pulmonary embolism or peripheral vascular embolism (97 cases, 0.4%), cardiovascular events such as heart failure and myocardial infarction (77 cases, 0.3%), and cerebral events such as infarction or hemorrhage (29 cases, 0.1%). Mortality occurred in 27 cases (0.1%). In this registry, the primary cause of death could not be precisely determined; however, among the 27 in-hospital deaths (0.1%), the following complications were recorded: pulmonary embolism/peripheral vascular embolism (n=4), respiratory complications (n=2), gastrointestinal complications (n=3), cerebral events (n=1), and intraoperative major-vessel injury (n=1). The remaining cases (n=16) involved other or unspecified complications.

Association between patient/procedure/surgeon factors and complication rates

The overall complication rate increased with age, increasing from 7.2% in patients aged 18-29 years to 18.6% in those aged ≥90 years (Figure 2). Complication rates also significantly differed among the age groups (p<0.01) (Table 5).

Figure 2.

Overall complication rates stratified by age group. The overall complication rate increased significantly with age (p<0.001), ranging from 7.2% in patients aged 18-29 years to 18.6% in those aged ≥90 years. This trend indicates a strong age-related increase in perioperative risk among patients undergoing adult spinal instrumentation surgery.

Table 5.

Association between Patient/Procedure/Surgeon Factors and Complication Rates.

Association Between age and complication rate
Age group (years)	No of cases (n)	Complication rate (%)	p-Value*
18-29	940	7.2	p<0.001
30-39	619	7.6
40-49	1,697	9.1
50-59	3,270	9.5
60-69	6,686	10.4
70-79	10,739	11.9
80-89	4,698	12.7
≥90	183	18.6
Association between pathology and complication rate
Pathology	No of cases (n)	Complication rate (%)	p-Value**
Degenerative	18,132	9.8	p<0.001
Deformity	4,451	13.9
Trauma	4,369	12.3
Tumor	1,006	13.3
Infection	749	13.4
Others	125	9.6
Association between number of fused levels and complications
Fusion levels group	No of cases (n)	Complication rate (%)	p-Value***
Short fusion (1, 2)	17,387	9.2	p<0.001
Medium fusion (3-6)	7,868	13.4
Long fusion (≥7)	3,090	15.8
Association between surgeon experience and complications
Surgeon experience (years)	No of cases (n)	Complication rate (%)	p-Value ****
<5	281	11.0	p<0.001
5-9	3,182	8.3
10-14	4,119	13.0
≥15	21,250	11.1

*Statistical comparisons between age subgroups were performed.

**Statistical comparisons between pathology subgroups were performed.

***Statistical comparisons between fusion-level subgroups were performed.

****Statistical comparisons between surgeon experience subgroups were performed.

The complication rate increased with an increase in the number of fused levels. Specifically, the complication rates were 8.3% for single-level fusion (n=11,740) and 11.2% for two-level fusion (n=5,647). When the degree of fusion was grouped into three categories, the complication rate was 9.2% for short fusions (1-2 levels), 13.4% for medium fusions (3-6 levels), and 15.8% for long fusions (≥7 levels). The complication rates differed significantly among the fusion-level subgroups (p<0.01) (Table 5).

Among the 28,832 cases, complication rates varied according to the surgeon's postgraduate experience: 11.0% for surgeons with <5 years of experience (n=281), 8.3% for those with 5-9 years of experience (n=3,182), 13.0% for surgeons with 10-14 years of experience (n=4,119), and 11.1% for those with ≥15 years of experience (n=21,250). The lowest complication rate was observed in the 5-9-year group, whereas the 10-14-year group had the highest complication rate (p<0.001).

Discussion

This nationwide registry-based study using the JSIS-DB comprehensively analyzed 28,832 adult patients who underwent spinal instrumentation surgery. The JSIS-DB is one of the largest datasets compiling information regarding demographic and surgical characteristics as well as perioperative complications associated with contemporary adult spinal surgery in Japan^6,13,15,16). The findings of this study provide important insights into the current clinical reality, clarify the influence of patient and surgical factors on complication risks, and will potentially contribute to improving the quality of medical care. The mean age of the patient cohort was 67.3 years, and most patients were in their 70s. These findings clearly reflect the aging population of Japan, where the demand for spinal surgery in elderly patients is expected to further increase¹⁷⁾. Degenerative diseases accounted for nearly two-thirds of all cases, with lumbar spinal stenosis and spondylolisthesis being the most frequent diagnoses. Nevertheless, trauma, deformity, tumors, and infection collectively accounted for more than one-third of the cases, indicating that spinal instrumentation is performed across a wide spectrum of diseases. Posterior approaches, including posterior and posterolateral fusion and posterior interbody fusion, predominated across all experience groups, which is consistent with previous reports stating that posterior fixation remains the standard surgical approach¹⁷⁾. However, anterior and combined anterior-posterior procedures were more frequently performed by experienced surgeons, who also performed a higher proportion of complex procedures such as scoliosis correction and tumor resections. Notably, surgeons with ≥15 years of postgraduate experience performed the widest variety of procedures and long fusions, whereas junior surgeons (<5 years) largely performed short-segment posterior fusions. These patterns suggest that case allocation is closely tied to training level, reflecting a stepwise acquisition of surgical expertise under supervision.

In adult spinal surgery with instrumentation, the overall complication rate within 14 days was 11.0%, with dural tears, nerve root disorders, and epidural hematomas being the most frequent events. This incidence was slightly lower than that reported in a 2011 nationwide survey⁶⁾. In that survey, the overall complication rate for spinal surgery was 10.4%, which increased to 15.6% for procedures involving instrumentation; thus, the overall complication rate appears to have decreased in the present study. However, systemic complications such as psychiatric disorders and respiratory complications were also observed among elderly patients, highlighting the need for vigilant perioperative management in this population. The perioperative mortality rate was 0.1%, which is low but cannot be overlooked because of the large case volume.

Complication rates increased progressively with age, reaching 18.6% in patients aged ≥90 years, and were correlated with surgical invasiveness, rising to 15.8% in long fusions (≥7 levels). Furthermore, the rates varied according to the underlying pathology and were higher in cases involving deformities than in those with other indications. These age-related trends are consistent with the findings of a recent nationwide registry report focusing on adult spinal deformity surgery in Japan, which demonstrated a 30-day complication rate of 11.8% as well as higher rates among older patients (13.0% in those aged ≥75 years vs. 6.2% in those aged 19-39 years)¹⁸⁾. Similarly, Yamato et al.¹⁹⁾ conducted a nationwide multicenter survey in Japan specifically addressing elderly patients with adult spinal deformities and reported that the incidence of perioperative complications increased significantly with advancing age. These observations confirm that advanced age is a major determinant of perioperative risk.

In a study based on the European Spine TANGO registry, which included the data for 168,583 surgical cases in 2024, the incidence of dural lesions was 2.95%; neurological complications, namely, motor dysfunction, radiculopathy, and sensory dysfunction, occurred in 0.38%, 0.34%, and 0.31% of the patients, respectively; and the in-hospital mortality rate was 0.02%²⁰⁾. In the JSIS-DB cohort, the corresponding rates were 2.5%, 1.4%, and 0.4% for dural tears, nerve root disorders, and spinal cord disorders, respectively, and the mortality rate was 0.1%. These findings indicate that the frequency of major neurological and fatal complications in Japan is broadly comparable to that reported in Europe, with slightly higher neurological and mortality rates that may be related to the older patient population and the fact that the JSIS-DB specifically includes spinal instrumentation surgeries, which are generally more invasive, unlike the overall spine surgery population captured by the Spine TANGO registry. Similarly, the American Spine Registry (ASR) Annual Report 2025, which analyzed 11,826 lumbar fusion procedures performed between 2015 and 2023, reported 30-day and 90-day readmission rates of 2.2% and 3.2%, respectively. Among the complications associated with readmission, infection accounted for 64.8% of the cases, followed by hematoma or wound complications (6.3%) and gastrointestinal, renal, or neurological complications (5.4%). Although the ASR does not provide specific rates for dural tears, neurological injuries, or in-hospital mortality, it allows longitudinal outcome monitoring within 90 days after surgery and serves as a national model for postoperative quality surveillance in the United States. Together with the JSIS-DB, which focuses specifically on spinal instrumentation surgeries, and the Spine TANGO registry, which encompasses a broader range of spinal procedures in Europe, these international datasets collectively offer valuable insights into the global landscape of perioperative complications associated with spine surgery. Interestingly, the association between surgeon experience and the complication rate was nonlinear. The lowest complication rate was observed in the 5-9-year group (8.3%), whereas the highest rate was in the 10-14-year group (13.0%). This trend has also been reported in previous nationwide surveys⁶⁾. Such paradoxical findings may reflect differences in the case mix, since mid-career surgeons, while still consolidating their technical skills, tend to take on more challenging cases. The quantitative contrasts between the 10-14-year and ≥15-year groups (a higher proportion of cases involving deformities and slightly longer constructs in the senior group) support the interpretation that differences in the case mix partly explain the nonlinear association between surgeon experience and complications. In contrast, despite managing the most complex procedures, the most experienced surgeons demonstrated a slightly lower complication rate (11.1%), which could be attributed to their accumulated technical proficiency and more refined perioperative management. Consistent with this perspective, Lau et al.²¹⁾ showed that greater operative experience in thoracolumbar 3-column osteotomy was linked to fewer neurological complications and shorter operative times, highlighting the importance of overcoming the learning curve. Similarly, a recent meta-analysis confirmed that experienced surgeons achieved lower complication rates and more favorable operative parameters in adult spinal deformity surgery²²⁾.

These findings have important clinical and educational implications. First, the elevated risk associated with older age and long fusions underscores the need for rigorous patient selection, meticulous perioperative management, and multidisciplinary care. Second, the clear stratification of surgical case complexity by surgeons' experience levels emphasizes the importance of structured training systems that ensure that junior surgeons begin with less complex cases and gradually progress to more demanding procedures. Finally, understanding risk profiles in relation to patient age, pathology, fusion extent, and surgeon experience may serve as an essential foundation not only for improving the quality of care in instrumented spine surgery but also for the development of structured educational curricula.

This study had several limitations that require consideration. First, although the JSIS-DB included data from a large number of cases nationwide, the data were limited to the perioperative period, and long-term outcomes such as revision surgery or functional recovery could not be assessed. Second, because 24.4% of the patients were discharged within 14 days after surgery, postoperative events occurring after discharge may not have been fully captured. Therefore, some degree of uncertainty persisted regarding the completeness of complication reporting for patients discharged within 14 days, and complications that typically occurred later are likely to have been underestimated. In particular, surgical-site infections were likely underreported, since international standards for procedures involving implants recommend at least 90 days of follow-up; therefore, this registry is not suitable for accurate evaluation of the incidence of surgical-site infections²³⁾. Third, the accuracy of complication reporting may vary across institutions, potentially leading to underestimation of event rates. Fourth, surgeons' experience was categorized solely by postgraduate years, which may not fully reflect their surgical proficiency. Despite these limitations, the strengths of this study include its large sample size, nationwide coverage, and the ability to stratify outcomes according to patient-, surgical-, and surgeon-related factors.

In conclusion, this registry-based analysis demonstrated that spinal instrumentation surgery in Japan is predominantly performed in elderly patients with degenerative diseases and most frequently performed using posterior approaches. The perioperative complication rates were influenced by age, surgical invasiveness, and surgeon experience. These findings provide real-world evidence to guide patient counseling, perioperative risk management, and surgical training and underscore the importance of registry-based research in improving the quality and safety of spinal surgery.

Author Contributions: H.A. analyzed the data, H.A. drafted the manuscript, A.M. supervised the analysis.

All authors designed and critically revised the study, acquired the data, interpreted the data, and approved the final version of the manuscript.

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

Ethics Approval: IRB approval: This study was reviewed and approved by the Spinal Instrumentation Society Review Board (IRB #15R) and adhered to the principles of the Declaration of Helsinki.

Informed Consent: This study was a research study using a database and was conducted on an opt-out basis, ensuring that research participants had the opportunity to decline participation, written or verbal consent was not obtained from the research participants.