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. 2025 Dec 9;15:7. doi: 10.1186/s13741-025-00637-2

Hypothyroidism as a risk factor for perioperative complications in lumbar spine surgery: a national database study

Yusong Zhang 1,#, Mingde Qiu 2,#, Weihao Chen 3,#, Zimo Ye 3, Luyi Cheng 2, Qinfeng Yang 4,✉, Lu Tao 5,✉, Lijun He 6,✉
PMCID: PMC12801521  PMID: 41361753

Abstract

Background

Hypothyroidism is a highly prevalent endocrine disorder increasingly recognized as a potential modifier of perioperative risk in orthopedic surgery. Emerging evidence indicates associations between hypothyroidism and adverse perioperative outcomes, including systemic complications and delayed recovery, in orthopedic populations. However, existing analyses remain limited by small sample sizes, lack of surgical subtype stratification, and insufficient focus on lumbar spine surgery (LSS) specifically. To address this gap, we leveraged data from the Nationwide Inpatient Sample (NIS) to clarify the association between hypothyroidism and perioperative complications in patients undergoing LSS.

Methods

A retrospective analysis was performed utilizing the NIS database (2013–2022). LSS patients were identified by ICD-9/10 codes and further divided into hypothyroid and non-hypothyroid cohorts. Propensity scores were calculated and matched in 1:1 ratios for patients with hypothyroidism to patients without hypothyroidism based on patient demographics, hospital characteristics, and Charlson Comorbidity Index, Perioperative complications were analyzed by multivariable logistic regression.

Results

Among 873,110 LSS patients, 11.66% were diagnosed with hypothyroidism. Hypothyroid patients were older (median age 64 versus 59 years, P < 0.001). Before stratification, hypothyroidism was associated with significantly increased odds ratios (ORs) for the following complications in the overall lumbar spine surgery patient cohort: sepsis, postoperative shock, postoperative delirium, acute cerebrovascular disease, acute myocardial infarction, congestive heart failure, deep vein thrombosis, pneumonia, pulmonary embolism, respiratory failure, urinary tract infection, transfusion, wound infection, wound dehiscence, in-hospital mortality, and prolonged length of stay (LOS) (P < 0.001 for all). After stratification, patients who underwent lumbar fusion alone demonstrated significantly elevated Odds Ratios (ORs) for all complications. In contrast, among those who underwent lumbar decompression alone or discectomy alone, the increases in ORs for wound infection and wound dehiscence were not statistically significant. Furthermore, for the discectomy-alone subgroup, the elevated ORs for postoperative shock and acute myocardial infarction also lacked statistical significance. For all other complications, the subgroups showed elevated ORs that were statistically significant.

Conclusions

This study suggests a correlation between hypothyroidism and a higher risk of complications in patients undergoing lumbar spine surgery. This finding indicates that surgeons should exercise heightened vigilance with lumbar surgery patients who have co-existing hypothyroidism.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13741-025-00637-2.

Keywords: Hypothyroidism, Nation wide inpatient sample, Lumbar surgery, Complications

Introduction

Hypothyroidism, a widely existing endocrine disease, can badly influence the bone health status and perioperative recovery, which is considered to be an important issue when deciding the appropriate time to perform lumbar spine surgery (LSS) (Williams 2013). In clinic, this condition disturbs bone homeostasis through reducing the trabecular microarchitecture rather than lowering bone mineral density (BMD), including elevated trabecular separation, cortical thinning and impaired biomechanical integrity (Leslie et al. 2020; Samelson et al. 2018; Poorman et al. 2018). The structural changes increase the risk of instrumentation failure and suboptimal osseointegration in spinal fusion, especially in elderly people with comorbidities (Poorman et al. 2018; Memtsoudis et al. 1976).

Beyond skeletal effects, hypothyroidism modulates perioperative outcomes through clinically relevant pathways: it hinders angiogenic responses critical for bone repair and induces immune dysregulation, contributing to delayed healing and a nearly twofold increased risk of postoperative infection (Bassett et al. 2010; Ross et al. 2016). Despite guidelines from the American Thyroid Association recommending preoperative thyroid-stimulating hormone (TSH) normalization to mitigate such risks (Ross et al. 2016), clinical implementation remains inconsistent, and risk stratification for hypothyroid patients undergoing LSS lacks robust evidence. LSS is a mainstay in the treatment of degenerative spinal conditions, but the effect of hypothyroidism as a possible risk factor for perioperative complications is still undetermined and controversial from the evidence pool of existing studies which were mostly performed in small scale or sing center and no resolution had been achieved for either the specific complication profile or the modifiers from surgery type (Memtsoudis et al. 1976; Vestergaard et al. 2005). In order to fill these gaps, we conducted an analysis using a large national database to elucidate whether hypothyroidism is associated with perioperative complications in LSS. By population-based approach and bigdata analysis, our study provides compelling evidence to help determine that hypothyroidism may be a clinical risk factor of perioperative complications of LSS and it informs preoperative risk stratification and targeted interventions for better surgical outcome.

Methods

Data source

To translate these mechanistic insights into actionable clinical evidence, we conducted a retrospective cohort study using the National Inpatient Sample (NIS) database, a nationally representative repository of de-identified inpatient healthcare records designed and maintained by the Agency for Healthcare Research and Quality (AHRQ) (Kurtz, et al., 2022). The NIS employs a stratified sampling methodology, encompassing approximately 20% of annual U.S. hospital discharges, with statistical weighting to generate population-level estimates reflective of the national inpatient demographic. The database aggregates comprehensive clinical variables, including patient demographics, diagnostic classifications (coded via ICD-9-CM and ICD-10-CM systems), procedural interventions (documented using CPT codes), perioperative complications, and discharge outcomes, thereby facilitating robust epidemiological analyses of inpatient care trends. This study was in line with the strengthening the reporting of cohort, cross-sectional, and case–control studies in surgery statement (Newman et al. 2018; Mathew et al. 2021).

Data collection

In this study, data were collected from the NIS database from 2013 to 2022. The collected data included demographic information, diagnoses, procedures, length of stay (LOS), hospital costs, and insurance types, as defined by the International Classification of Diseases, 9th Revision (ICD-9) diagnosis and procedure codes.

Patients who have undergone LSS, including lumbar fusion, lumbar decompression, and discectomy were identified using ICD-9-CM procedure codes (81.06, 81.07, 81.08, 03.09, 80.51) and ICD-10-CM codes (Supplementary documents) (n = 873,110). These patients were then divided into two groups: those with hypothyroidism and those without hypothyroidism, based on ICD-9-CM codes (244.x, 243) and ICD-10-CM codes (E03.x, E02, E89).

Primary endpoints of this study were defined as common in-hospital postoperative complications following LSS surgery, which were categorized into four major types: medical complications such as sepsis and postoperative shock, with other medical complications detailed in Table 2; wound complications; in-hospital mortality; and prolonged length of stay (LOS).

Table 2.

Major complications in patients undergoing lumbar spine surgery

Perioperative complications Hypothyroidism N (%) Whole non-hypothyroidism N (%) P value Matched non-hypothyroidism N (%) P value
Medical complications
 Sepsis 768 (0.75%) 6,170 (0.79%) 0.127 1,410 (1.39%) < 0.001
 Postoperative shock 96 (0.09%) 665 (0.08%) 0.409 260 (0.26%) < 0.001
 Postoperative delirium 1,396 (1.37%) 6,663 (0.86%) < 0.001 2,109 (2.12%) < 0.001
 Acute cerebrovascular disease 1,035 (1.02%) 6,472 (0.84%) < 0.001 1,560 (1.53%) < 0.001
 Acute myocardial infarction 2,689 (2.64%) 18,927 (2.45%) < 0.001 3,137 (3.08%) < 0.001
 congestive heart failure 2,850 (2.81%) 13,566 (1.76%) < 0.001 4,547 (4.47%) < 0.001
 Deep vein thrombosis 507 (0.49%) 3,843 (0.50%) 1.000 867 (0.85%) < 0.001
 Pneumonia 1,352 (1.33%) 9,456 (1.23%) 0.005 2,253 (2.21%) < 0.001
 Pulmonary embolism 315 (0.31%) 2,246 (0.29%) 0.309 538 (0.53%) < 0.001
 Respiratory failure 1,532 (1.51%) 8,969 (1.16%) < 0.001 2,493 (2.45%) < 0.001
 Urinary tract infection 4,313 (4.24%) 21,452 (2.78%) < 0.001 5,439 (5.34%) < 0.001
 Transfusion 8,895 (8.74%) 45,972 (5.96%) < 0.001 11,173 (10.98%) < 0.001
Wound complications
 Wound infection 470 (0.46%) 3,681 (0.48%) 0.503 638 (0.63%) < 0.001
 Wound dehiscence 222 (0.22%) 1,614 (0.21%) 0.560 370 (0.36%) < 0.001
Other complications
 Deaths 168 (0.17%) 1,597 (0.21%) 0.005 457 (0.45%) < 0.001
 Prolonged LOS 39,032 (38.4%) 241,935 (31.37%) < 0.001 45,458 (44.67%) < 0.001
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Notably, acute cerebrovascular disease (ACVD) in this study was defined as cerebral dysfunction caused by cerebrovascular abnormalities, including intracerebral hemorrhage, cerebral insufficiency, cerebral arteritis, and cerebral artery occlusion. Patients with hypothyroidism exhibited a significantly increased risk of postoperative ACVD, especially those with impaired immune function, unstable blood pressure, and hemodynamic changes. Previous studies have demonstrated that hypothyroidism may induce immune-endocrine regulatory imbalance, which elevates the incidence of cerebrovascular diseases, thereby exacerbating postoperative complications and delaying functional recovery (Duntas and Feldt-Rasmussen 2025; Yuan et al. 2025). Beyond such systemic complications, wound complications were specifically defined as wound infection and wound dehiscence. The inclusion of these endpoints is justified by substantial evidence linking hypothyroidism to impaired wound healing. For instance, a matched control analysis by Vakharia et al. demonstrated that patients with hypothyroidism undergoing primary single-level anterior cervical discectomy and fusion (ACDF) have a significantly elevated risk of postoperative non-healing surgical wounds (OR 2.27, P < 0.001) (Wen et al. 2025). While this study focused on the cervical spine, the underlying pathophysiological mechanisms are highly relevant to lumbar procedures. This clinical observation is mechanistically supported by fundamental animal research, where Contreras-Jurado et al. showed that mice lacking thyroid hormone receptors exhibit defective keratinocyte proliferation and delayed re-epithelialization, leading to wound dehiscence (Zou et al. 2025). ll complications were adjudicated strictly in accordance with the International Classification of Diseases, 9th and 10th Revisions, diagnostic coding criteria to ensure diagnostic accuracy and inter-study comparability. Postoperative complications were selected based on the authors’ expertise and a review of existing publications (De Stefano et al. 2022; Hollenbeck et al. 2020; Huang et al. 2023a; Maman et al. 2024; Morishita et al. 2019; Naftchi et al. 2023; Ordoyne et al. 2024). Other outcomes analyzed incorporated in-hospital mortality, prolonged LOS. LOS was recorded as the number of days from the hospital admission until the hospital discharge date. Extended LOS was defined as any duration of hospitalization exceeding the 75th percentile of all hospital stays (Golinvaux, et al., 2014).

Since the NIS collects inpatient hospitalization data, the term “perioperative period” in this study specifically refers to the duration from hospital admission to discharge. Finally LOS were used to quantify resource utilization. Patients with hyperthyroidism (n = 2,269), those with missing demographic or clinical variables (n = 17,251), and those aged < 18 years (n = 14,417) were excluded. Patients with AIDS (n = 1,092) and those with metastatic cancer (n = 4,671) were excluded. After exclusions, 873,110 records were retained for analysis (Fig. 1).

Fig. 1.

Fig. 1

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Flowchart of eligibility criteria (inclusion/exclusion) for lumbar spine surgery patients. ICD-9, international classification of diseases (ninth edition) clinical modification; ICD-10, international classification of diseases (tenth edition) clinical modification; LSS, lumbar spine surgery

Statistical analysis

All statistical analyses were performed using IBM SPSS Statistics 26.0 (IBM Corp, Armonk, NY). A two-sided α level of 0.05 (P < 0.05) was established as the threshold for statistical significance. Continuous variables are presented as medians; categorical variables, as frequencies (percentages). Baseline characteristics were compared using either the Wilcoxon rank test for continuous variables and the Pearson χ2 test for categorical variables (Table 1). In this cross-sectional analysis, the cohort consisted of patients diagnosed with lumbar spine surgery (LSS). To account for possible confounders when comparing perioperative complications, propensity score matching (PSM) was employed to address differences between groups. PSM was performed according to a described method 0. A 1:1 fixed ratio of nearest neighbor matching between hypothyroid and non-hypothyroid cohorts was performed. Selected variables for PSM were all variables supplied by the NIS including age group, gender, race, bed size of hospital, teaching status of hospital, Chronic pulmonary disease, Diabetes, Drug abuse, Hypertension, Alcohol abuse, Charlson comorbidity index subgroup, location of hospital and admission type 0. Despite inclusion in the Charlson Comorbidity Index (CCI), diabetes mellitus (DM) and chronic lung disease (CLD) were analyzed as independent variables—prior studies show the composite CCI cannot fully reflect their specific impacts on postoperative recovery; DM affects immunity, wound healing, and infection risk, while CLD impairs postoperative respiratory function and oxygenation, so they were included separately in the model to precisely evaluate their independent effects on postoperative complications in hypothyroid patients (Lin et al. 2019; Huffman et al. 2023; Brown et al. 2025; Haeuser et al. 2021). To control potential confounding factors, all relevant demographic characteristics as presented in Table 1 (including age, biological sex, etc.) as well as surgical type (elective vs. emergency surgery) were incorporated into the statistical model for adjustment (Yang et al. 2022a). We employed a multivariable regression model to evaluate the independent effect of hypothyroidism on postoperative complications while controlling for these confounding variables. This ensured the observed association was unconfounded by extraneous factors.

Table 1.

Demographic characteristics of lumbar spine surgery patients with and without hypothyroidism

Variable Hypothyroidism Whole non-hypothyroidism P value Matched non-hypothyroidism P value
N 101,763 771,347 – – –
Age in years, median 66 59 < 0.001 – –
Age group n (%) < 0.001 0.112
 18–44 7,031 (6.91%) 145,702 (18.89%) 7,196 (7.07%)
 45–64 40,609 (39.91%) 352,998 (45.76%) 40,925 (40.22%)
 65–74 33,555 (32.97%) 182,137 (23.61%) 33,391 (32.81%)
≥ 75 20,568 (20.21%) 90,510 (11.73%) 20,251 (19.90%)
Gender n (%) < 0.001 0.05
 Male 23,301 (22.90%) 397,323 (51.51%) 23,678 (23.27%)
 Female 78,462 (77.10%) 374,024 (48.49%) 78,085 (76.73%)
Race n (%) < 0.001 0.111
 White 83,463 (82.02%) 579,887 (75.18%) 83,507 (82.06%)
 Black 3,931 (3.86%) 61,716 (8.01%) 3,994 (3.92%)
 Hispanic 4,363 (4.29%) 45,393 (5.88%) 4,404 (4.33%)
 Asian or Pacific Islander 864 (0.85%) 9,420 (1.22%) 847 (0.83%)
 Native American 337 (0.33%) 3,344 (0.43%) 268 (0.26%)
 Other 8805 (8.65%) 71,587 (9.28%) 8,743 (8.59%)
Bed size of hospital n (%) < 0.001 0.337
 Small 18,729 (18.40%) 140,279 (18.19%) 18,532 (18.21%)
 Medium 25,328 (24.90%) 188,965 (24.50%) 25,210 (24.77%)
 Large 57,706 (56.71%) 442,103 (57.32%) 58,021 (57.02%)
Type of hospital n (%) < 0.001 0.662
 Nonteaching 37,453 (36.80%) 294,087 (38.13%) 37,358 (36.71%)
 Teaching 64,310 (63.20%) 477,260 (61.87%) 64,405 (63.29%)
Hospital location n (%) < 0.001 0.494
 Rural 4,180 (4.11%) 39,975 (4.41%) 4,119 (4.05%)
 Urban 97,583 (95.89%) 737,372 (95.59%) 97,644 (95.95%)
Charlson comorbidity index subgroup < 0.001 0.926
 0 3 (0.00%) 199,936 (25.92%) 3 (0.00%)
 1 12,580 (12.36%) 217,839 (28.24%) 12,609 (12.39%)
 2 26,032 (25.58%) 172,424 (22.35%) 25,898 (25.45%)
 ≥ 3 63,148 (62.05%) 181,148 (23.48%) 63,253 (62.16%)
Admission type n (%) < 0.001 0.019
 Non-elective 12,949 (12.72%) 110,739 (14.36%) 13,305 (13.07%)
 Elective 88,814 (87.27%) 660,608 (85.64%) 88,458 (86.9%)
Location/teaching status of hospital n (%) < 0.001 0.765
 Rural 4,180 (4.11%) 33,975 (4.40%) 4,119 (4.05%)
 Urban nonteaching 33,273 (32.69%) 260,112 (33.72%) 33,239 (32.66%)
 Urban teachin 64,310 (63.19%) 477,260 (61.88%) 64,405 (63.29%)
Chronic pulmonary disease < 0.001
n (%) 0.073
 Yes 20,794 (20.43%) 118,389 (15.35%) 21,121 (20.76%)
 No 80,969 (79.57%) 652,958 (84.65%) 80,642 (79.24%)
Diabetes n (%) < 0.001 0.664
 Yes 25,602 (25.16%) 145,415 (18.85%) 25,687 (25.24%)
 No 76,161 (74.84%) 625,932 (81.15%) 76,076 (74.76%)
Drug abuse n (%) < 0.001 0.439
 Yes 1,375 (1.35%) 13,030 (1.69%) 1,335 (1.31%)
 No 100,388 (98.65%) 75,8317 (98.31%) 100,428 (98.69%)
Hypertension n (%) < 0.001 0.198
 Yes 65,577 (64.44%) 399,388 (51.78%) 65,299 (64.17%)
 No 36,186 (35.56%) 371,959 (48.22%) 36,464 (35.83%)
Alcohol abuse n (%) < 0.001 0.499
 Yes 942 (0.93%) 12,598 (1.63%) 913 (0.89%)
 No 100,821 (99.07%) 758,749 (98.37%) 100,850 (99.01%)
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Results

Following the exclusion of cases with incomplete data, a total of 873,110 lumbar spine utilizing the NIS database (Fig. 1). Of these, 101,763 cases (11.66%) involved patients diagnosed with hypothyroidism. Patient demographic characteristics (e.g., age, biological sex, race) and institutional variables are comprehensively summarized in Table 1. Postoperative complication rates are delineated in Table 2. The results of the unadjusted and adjusted logistic regression models analyzing the association between hypothyroidism and complications in the lumbar spine surgery cohort are presented in Figs. 3 and 4, respectively.

Fig. 3.

Fig. 3

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Unadjusted multivariate logistic regression analysis of complications in patients undergoing lumbar spine surgery with and without hypothyroidism. OR, odds ratio; CI, confidence interval

Fig. 4.

Fig. 4

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Adjusted multivariate logistic regression analysis of complications in patients undergoing lumbar fusion surgery with and without hypothyroidism. OR, odds ratio; CI, confidence interval. The data has been adjusted for the demographic characteristics of LSS patients, as outlined in Table 1

Prevalence of hypothyroidism in lumbar spine surgery cohorts

Analysis of the NIS database identified 873,110 lumbar spine surgeries conducted between 2013 and 2022. The prevalence of hypothyroidism among this cohort demonstrated a progressive upward trajectory, rising from 9.84% in 2013 to 13.98% in 2022, with only marginal attenuation observed in 2022 relative to preceding years. The aggregate decadal prevalence of hypothyroidism was 11.66% (Fig. 2).

Fig. 2.

Fig. 2

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Annual incidence of hypothyroidism in patients undergoing lumbar spine surgery from 2013 to 2022. The values in this figure are derived from weighted national discharge estimates based on the unweighted NIS data, in order to estimate the morbidity of patients with or without hypothyroidism

Demographic profile of hypothyroid patients

Before propensity score matching, the majority of hypothyroid and non-hypothyroid patients undergoing LSS were categorized within the 45–64 age group. Patients with hypothyroidism were significantly older (P < 0.001), with a median age of 64 years compared to 59 years in the non-hypothyroid group. A significantly higher proportion of hypothyroid patients fell into older age categories (65–74 and ≥ 75 years, P < 0.001). The hypothyroid group demonstrated a pronounced female predominance (P < 0.001). White individuals comprised a significantly larger proportion of the hypothyroid cohort (P < 0.001), indicating distinct demographic patterns in disease prevalence. Hospital characteristics showed significant differences in teaching status (P < 0.001), as hypothyroid patients were more frequently treated in teaching hospitals. Rural hospital utilization was comparable between the two groups (P < 0.001). Hypothyroid patients carried substantially higher comorbidity burdens, particularly in the Charlson comorbidity index subgroup with scores ≥ 3 (P < 0.001). Elective admissions were more prevalent in the hypothyroid cohort (P < 0.001). Significant differences were observed in hospital bed size categories (P < 0.001). We also observed significant intergroup differences in chronic pulmonary disease, diabetes, drug abuse, hypertension, and alcohol abuse (p < 0.001). After propensity score matching, all baseline variables for hypothyroidism were successfully matched (12/14, P > 0.05) except Gender (p = 0.05) and Admission type (P = 0.19) (Table 1).

Perioperative surgical and systemic complications

Forest plot analysis revealed significant disparities in perioperative complications between hypothyroid and non-hypothyroid patients undergoing surgical procedures. Hypothyroid patients demonstrated markedly elevated rates of sepsis (P < 0.001), congestive heart failure (P < 0.001), postoperative delirium (P < 0.001), acute cerebrovascular disease (P < 0.001), deep vein thrombosis (P < 0.001), acute myocardial infarction (P < 0.001), urinary tract infection (P < 0.001), and postoperative shock (P < 0.001), indicating heightened systemic vulnerability. A significantly increased incidence of pulmonary embolism (P < 0.001) was observed in hypothyroid patients, consistent with metabolic dysregulation associated with thyroid dysfunction. Respiratory complications, including acute respiratory failure (P < 0.001) and pneumonia (P < 0.001), further underscored the systemic perioperative risks in this population.

Following propensity score matching and multivariable adjustment for covariates such as age and comorbidities, hypothyroid patients maintained significantly higher risks of all postoperative complications (P < 0.001) (Figs. 3 and 4). After stratifying lumbar spine surgery (LSS) into three subtypes—lumbar fusion, lumbar decompression, and discectomy—distinct patterns of risk association emerged. In the lumbar fusion cohort, hypothyroid patients demonstrated consistently elevated risks for all perioperative complications compared to non-hypothyroid patients, both before and after multivariable adjustment (unadjusted P < 0.01; adjusted P < 0.01) (Figs. 3 and 4). Among patients undergoing lumbar decompression alone, hypothyroidism was associated with significantly increased risks for the majority of complications (P < 0.05), with the exception of wound dehiscence (unadjusted P = 0.137; adjusted P = 0.137) and wound infection (unadjusted P = 0.170; adjusted P = 0.170), which did not reach statistical significance (Figs. 3 and 4). In the discectomy-only subgroup, hypothyroid patients showed significantly higher risks for most complications (unadjusted P < 0.05; adjusted P < 0.05). However, no statistically significant associations were observed for postoperative shock (unadjusted P = 0.628; adjusted P = 0.568), acute myocardial infarction (unadjusted P = 0.008; adjusted P = 0.129),or wound infection (unadjusted P = 0.798; adjusted P = 0.483) after adjustment (Figs. 3 and 4).

Discussion

This study aims to clarify the association between hypothyroidism and perioperative complications in patients undergoing lumbar spine surgery. With the advancement of scientific research, a growing body of evidence suggests that endocrine disorders increase the risk of various perioperative complications. For instance, a study by Huang et al. demonstrated that hypothyroidism is associated with increased complications and prolonged hospital stays in patients undergoing total hip arthroplasty (Huang et al. 2023b). Although some studies indicate a correlation between hypothyroidism and elevated perioperative complications in various surgeries, data on its association with postoperative complications in lumbar spine surgery remain limited (Ladenson et al. 1984; Murkin 1982; Worku et al. 2015). Our findings reveal a significant relationship between hypothyroidism and perioperative complications in patients undergoing lumbar spine surgery, indicating that hypothyroidism is robustly associated with a higher risk of multiple postoperative complications. Furthermore, our study observed an increasing annual incidence of hypothyroidism, rising from 9.84% in 2013 to a peak of 14.09% in 2021, before slightly declining to 13.98% in 2022. The overall incidence of hypothyroidism over the ten-year period (2013–2022) was 11.66%. In comparison, another study reported an overall incidence of 9.4% from 2004 to 2014 among lumbar spine surgery patients, also derived from the NIS database (Luther et al. 2021). This suggests a progressive upward trend in the prevalence of hypothyroidism. Alternative explanations for the rising incidence of hypothyroidism must also be considered, including potential overdiagnosis or misclassification of the condition, along with a gradual improvement in the accuracy of medical coding by healthcare professionals, both contributing to an apparent increase in recorded cases.

Hypothyroidism has significant clinical implications in the surgical setting. In many surgical specialties, particularly in cardiovascular surgery, it is associated with greater perioperative risks (Vakharia et al. 2020). This means that the presence of hypothyroidism as a comorbidity can have a profound impact on postoperative cardiovascular complications in surgical patients. In our study, hypothyroidism significantly increased the risk of cardiovascular system complications in patients undergoing lumbar spine surgery, including acute cerebrovascular disease (OR: 1.51, 95% CI: 1.40–1.64), acute myocardial infarction (OR: 1.17, 95% CI: 1.11–1.24), congestive heart failure (OR: 1.65, 95% CI: 1.57–1.73), and deep vein thrombosis (OR: 1.68, 95% CI: 1.50–1.87). Vakharia et al. investigated 69,584 Medicare patients who underwent single or two-level lumbar fusion and found that patients with hypothyroidism had a significantly higher risk of complications, including acute myocardial infarction (OR: 4.51, 95% CI: 2.89–7.04) and deep vein thrombosis (OR: 1.97, 95% CI: 1.59–2.44)(Vakharia et al. 2020). These findings are similar to those in our study. However, contradictory results were observed in another study by Luther et al., who concluded that hypothyroidism was a protective factor for acute myocardial infarction and found that hypothyroidism reduced the in-hospital mortality rate in lumbar spine surgery patients (Luther et al. 2021). Although both our study and that of Luther et al. used the NIS database, our data spanned from 2013 to 2022, while Luther et al.’s data covered 2004 to 2014, and the data analysis methods differed. We used propensity score-matched results, which could explain the differing outcomes.

Our study results demonstrate that hypothyroidism was associated with a higher risk of postoperative sepsis, pneumonia, and urinary tract infections, with the following odds ratios (ORs): sepsis (OR: 1.81, 95% CI: 1.66–1.98), pneumonia (OR: 1.67, 95% CI: 1.56–1.78), and urinary tract infection (OR: 1.128, 95% CI: 1.23–1.33). Thyroid hormones (THs) are closely linked to the immune system, and hypothyroidism is generally considered to impair immune function, leading to a weakened immune response. Early studies in the 1970 s and 1980 s suggested that during bacterial pneumonia, thyroid hormones directly influence human leukocytes. Administration of thyroid hormones has been shown to enhance the phagocytic activity of neutrophils and promote lymphocyte proliferation, thereby improving leukocyte function (Adelberg et al. 1971; Balázs et al. 1980). Additionally, other studies have suggested that THs can directly regulate the proliferation and activation of T cells. A meta-analysis based on an institutional database of patients undergoing joint arthroplasty also identified hypothyroidism as a risk factor for periprosthetic joint infections (Tan et al. 2016). Moreover, Luther et al. found that hypothyroidism increases the risk of infection in patients following lumbar spine surgery (Luther et al. 2021). Given the deficiency of thyroid hormones in patients with hypothyroidism, it remains unclear whether this condition consequently leads to impaired immune function, a question that requires further investigation for confirmation.

On the other hand, our study also found that hypothyroidism is associated with postoperative respiratory failure in lumbar spine surgery patients, increasing the risk of respiratory failure postoperatively, as indicated by a respiratory failure odds ratio (OR) of (1.64 95% CI: 1.53–1.75). There is a significant association between hypothyroidism and respiratory failure, which may affect respiratory system function through several mechanisms, thereby increasing the risk of respiratory failure in postoperative lumbar spine patients. Hypothyroidism can cause generalized muscle weakness, including the respiratory muscles (such as the diaphragm and intercostal muscles), leading to reduced respiratory drive and insufficient ventilation (Fariduddin et al. 2025). Hypothyroidism may also reduce vital capacity, impair diffusing capacity, and cause ventilation-perfusion mismatch, all of which can negatively impact gas exchange, leading to hypoxemia or hypercapnia (Sadek et al. 2017). Additionally, hypothyroidism may reduce the central nervous system’s sensitivity to carbon dioxide, weakening the body’s ventilatory response to insufficient pulmonary ventilation, hypoxemia, and hypercapnia, thus diminishing respiratory drive(Milla and Zirbes 2012; Ladenson et al. 1988). This is especially evident during sleep, with studies showing that approximately 3.1% of patients with obstructive sleep apnea hypopnea syndrome (OSAHS) are diagnosed with hypothyroidism(Lin et al. 1992). These factors may explain why hypothyroidism increases the risk of respiratory failure in lumbar spine surgery patients.

Delirium is one of the common postoperative complications following lumbar spine surgery and has garnered widespread attention (Fineberg et al. 2013; Yang et al. 2022b). According to existing studies, postoperative delirium after lumbar spine surgery is associated with various factors. Numerous studies have shown that postoperative delirium is linked to factors such as inflammatory markers, age, biological sex, and preoperative anxiety (Yang et al. 2022b; Pan et al. 2019; Mou et al. 2023). Our findings indicate that hypothyroidism also associated with a higher risk of postoperative delirium in lumbar spine surgery patients (OR: 1.53, 95% CI: 1.53–1.64). Furthermore, in the study by Vakharia et al., hypothyroidism was found to increase the risk of postoperative delirium (OR: 4.54, 95% CI: 2.48–8.33) (Vakharia et al. 2020), which is consistent with our results.

Our findings demonstrate that hypothyroidism is associated with prolonged hospitalization, and elevated mortality in patients undergoing lumbar spine surgery. Specifically, hypothyroid patients exhibited significantly prolonged LOS (OR: 1.33, 95% CI: 1.31–1.36) and increased mortality (OR: 2.63, 95% CI: 2.20–3.15). These results are consistent with the study by Vakharia et al.(Vakharia et al. 2020), which similarly identified hypothyroidism as a risk factor for higher 90-day readmission rates following lumbar procedures. However, in contrast to our findings, Luther et al. (2021) unexpectedly reported a protective effect of hypothyroidism against postoperative mortality in lumbar surgery patients. The divergent results may be explained by methodological distinctions, particularly regarding the stratification of surgical procedures, sample size considerations, and inconsistent covariate adjustment in the regression models. Notably, our study further identified an increased risk of postoperative blood transfusion in hypothyroid patients (OR: 1.30, 95% CI: 1.26–1.34). This finding may inform preoperative blood preparation strategies for hypothyroid patients undergoing lumbar spine surgery.

This study provides a preliminary exploration of the association between hypothyroidism and postoperative complications following lumbar surgery, offering new insights into the impact of thyroid dysfunction on various complications related to lumbar procedures. However, several limitations should be acknowledged. Firstly, due to the cross-sectional design, we are unable to establish a causal relationship between hypothyroidism and the observed complications. Secondly, as with other studies utilizing large databases, potential coding discrepancies and data entry errors may exist in retrospective analyses. Additionally, although we adjusted for several confounding factors, unmeasured variables may still influence the outcomes. And the lack of data on hypothyroidism severity and control necessitated the use of a comorbidity index to assess overall patient status. Consequently, it should be recognized that this methodological constraint may limit the interpretability of the observed associations. Although hypothyroid patients were identified using specific ICD-9 and ICD-10 codes, the possibility of overdiagnosis or misclassification cannot be excluded. Future research should employ longitudinal designs to further investigate the underlying mechanisms linking hypothyroidism and delirium. Moreover, expanding the sample size and including more diverse populations would help validate the generalizability of our findings. Despite these limitations, the results of this study provide valuable references for the prevention and management of complications in hypothyroid patients in clinical practice.

Conclusion

In summary, our findings demonstrate that hypothyroidism is associated with an elevated risk of postoperative complications. Further prospective studies are warranted to determine whether optimization of thyroid function can mitigate this risk. This study provides a valuable reference for developing clinical strategies aimed at reducing postoperative complications following lumbar spine surgery.

Supplementary Information

Supplementary Material 1. (55.5KB, pdf)

Acknowledgements

Not applicable.

Clinical trial number

Not applicable.

Study registration

Not applicable.

Authors’ contributions

LT and LJH designed the study; MDQ and LYC,ZMY and WHC carried out data collection; MDQ and WHC wrote the manuscript. All authors read and approved the final manuscript.

Funding

This research did not receive any funding or financial support.

Data availability

This study was conducted using data from the Nationwide Inpatient Sample (NIS) database, which constitutes part of the Healthcare Cost and Utilization Project (HCUP) sponsored by the Agency for Healthcare Research and Quality (AHRQ). The direct web link to the database is: [https://www.ahrq.gov/data/hcup/index.html](https://www.ahrq.gov/data/hcup/index.html).

Declarations

Ethics approval and consent to participate

This study did not involve any direct research on human participants or animals conducted by the authors. Access to the original data used in this study requires administrative approval, and the co-authors’ institutional affiliations were granted permission by the Agency for Healthcare Research and Quality (AHRQ) to utilize the Healthcare Cost and Utilization Project (HCUP) nationwide database. However, because our observational study relied on de-identified, publicly available data, it was deemed exempt from ethical review by the Institutional Review Board (IRB) of Nanfang Hospital, Southern Medical University. Furthermore, the data collected in this study did not require additional anonymization prior to analysis. All methods were performed in accordance with relevant guidelines and regulations.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.

Footnotes

Publisher’s Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Yusong Zhang, Mingde Qiu and Weihao Chen have contributed equally to this manuscript.

Contributor Information

Qinfeng Yang, Email: breezeyoung1@i.smu.edu.cn.

Lu Tao, Email: 317147917@qq.com.

Lijun He, Email: 2260955183@qq.com.

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

Supplementary Material 1. (55.5KB, pdf)

Data Availability Statement

This study was conducted using data from the Nationwide Inpatient Sample (NIS) database, which constitutes part of the Healthcare Cost and Utilization Project (HCUP) sponsored by the Agency for Healthcare Research and Quality (AHRQ). The direct web link to the database is: [https://www.ahrq.gov/data/hcup/index.html](https://www.ahrq.gov/data/hcup/index.html).

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