Thrombotic complications are a feared cause of morbidity and mortality following thoracolumbar spine surgery. Venous thromboembolism (VTE), manifesting primarily as deep venous thrombosis (DVT) or pulmonary embolism (PE), is the most commonly reported complication [1,2]. Although overall uncommon, the incidence of VTE varies widely across studies. Reported rates of DVT following thoracolumbar procedures range between 0.3% and 31%, while PE rates range between 0.2% and 37.5% [3]. Postoperative VTEs are associated with significant morbidity, increased mortality, prolonged hospitalization, and up to a threefold increase in healthcare costs [4–6]. Cerebrovascular accident (CVA), another potential thrombotic complication, accounts for approximately 10% of in-hospital mortality following thoracolumbar procedures [7].

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of coronavirus disease 2019 (COVID-19) has been strongly associated with a hypercoagulable state [8,9]. Both VTE and CVA are known complications of COVID-19 [10]. Emerging evidence suggests that hypercoagulability may persist long after severe infection, with the phenomenon of “long COVID” garnering increasing attention [11,12]. In addition, case reports have documented thromboembolic events after vaccination [13]. According to the Centers for Disease Control and Prevention, seroprevalence data indicate that approximately 97% of the US population has either been infected by SARS-CoV-2 or vaccinated against it [14]. However, whether this widespread exposure has impacted baseline coagulability is not well understood.

Some evidence suggests that a history of severe COVID-19, such as COVID-19 requiring hospitalization, is more strongly associated with a persistent prothrombotic state [11]. At the height of the pandemic, high infection rates resulted in mass hospitalizations worldwide. In the United States, the cumulative hospitalization rate between May 2020 and April 2021 was 1,093 per 100,000 individuals [15]. Rates varied by age, ranging from approximately 0.4% in individuals younger than 40 to 9.2% in those older than 60 [16]. As vaccines became available, mounting evidence showed that vaccination reduces the incidence of severe infection and mortality [16,17]. Nevertheless, as of May 2023, an estimated 19% of the US population remained unvaccinated, 31% had not completed the primary series, and 83% had not received an updated booster [18].

Numerous studies have examined differences in healthcare delivery and outcomes before and after the COVID-19 pandemic [19]. However, there is a paucity of data on thrombotic complications following spine surgery in the post-pandemic era. Further, no studies have evaluated the potential influence of non-vaccinated status or a history of severe infection. The present study aimed to compare the rates of VTE and CVA after thoracolumbar spine surgery in the post-COVID era with those observed pre-COVID. Importantly, not all patients in the post-COVID cohort had a history of infection with COVID-19; rather, this group represents a surgical population potentially affected by environmental, immunologic, and systemic changes in the wake of the pandemic. Subgroup analyses were conducted to isolate the effect of vaccination status and prior COVID-19 hospitalization. We hypothesized that thrombotic complication rates would be higher in the post-COVID cohort.

In this large retrospective cohort study, patients undergoing thoracolumbar spine surgery in the post-COVID era demonstrated an increased risk of thrombotic complications compared with pre-COVID rates. Notably, unvaccinated patients and those with a history of COVID-19–related hospitalization were at the highest risk.

Our results are consistent with prior studies examining thrombotic risk in surgical patients during the COVID-19 era. In a large cohort of orthopedic procedures, including lumbar fusion, Johnson et al. [24] reported increased VTE risk among patients diagnosed with COVID-19 within 90 days of surgery. Similarly, Chehrassan et al. [25], in a single-center study from Iran, observed higher rates of DVT, PE, and MI in the post-COVID era. Using the American College of Surgeons National Surgical Quality Improvement Program database, Song et al. [18] demonstrated that patients undergoing spine surgery in 2020 experienced longer hospital stays and higher rates of DVT, pneumonia, and sepsis. However, their analysis was limited to the early pandemic, before vaccines became widely available and infection rates began to decline.

Although vaccination protects against severe SARS-CoV-2 infection, thrombotic complications have also been reported following vaccination [26]. In our cohort, the odds of VTE were increased regardless of vaccination status, although statistical significance was reached only in non-vaccinated patients. Demographic factors are unlikely to account for this difference, as unvaccinated and vaccinated groups were comparable in age, sex, and comorbidities, and these variables were adjusted for in multivariable analysis. However, interpretation is limited by the relatively small number of vaccinated patients in our dataset and the inability to determine whether vaccinated individuals may have had unrecognized prior infection with SARS-CoV-2. Thus, the clinical relevance of vaccination status to postoperative outcomes remains uncertain. If immunization does play a role, additional investigation is warranted to clarify the underlying mechanisms. For example, Macanu et al. [27] reported that complications after elective bariatric surgery increased only when COVID-19 was diagnosed postoperatively, not preoperatively. Further research in spine surgery should evaluate whether vaccination mitigates the risk of postoperative complications by reducing susceptibility to nosocomial COVID-19 infection, which remains an independent concern.

Existing literature suggests that COVID-19–induced hypercoagulability may be driven by systemic inflammation and cytokine storm, particularly in severe infections [28]. Hospitalization can therefore serve as a proxy for illness severity [29]. In the present study, patients with a history of COVID-19–related hospitalization had more than double the odds of postoperative VTE, even after adjusting for demographic variables and comorbidities. This finding is consistent with prior reports. For example, the Association of Anaesthetists of Great Britain and Ireland recommends that patients with prior moderate-to-severe COVID-19 be managed as a distinct high-risk category for elective surgery [30]. The American Society of Anesthesiologists similarly advises incorporating the severity of prior infection, ongoing symptoms, and vaccination status into perioperative risk assessment [30]. Our results support these recommendations and add evidence that previously hospitalized patients represent a particularly high-risk group for thrombotic complications. Collectively, these findings reinforce the importance of integrating COVID-19 history, vaccination status, and infection severity into preoperative risk stratification for thoracolumbar spine surgery.

This study has several limitations. First, the use of a large administrative database provided a substantial sample size and statistical power, but also increased the likelihood of detecting minor differences that may be statistically significant yet clinically modest. However, the database was uniquely suited for this research, as our goal was to evaluate national-scale trends. Nonetheless, both effect size and statistical significance should be considered when interpreting the findings. Second, patients were identified using ICD and CPT codes, which were designed for billing rather than research. While coding inaccuracies are possible, the complications and procedures evaluated are common and therefore less prone to coding errors compared with niche procedures or rare diagnoses. Inclusion of patients from diverse payer types reduces selection bias related to insurance status. Lastly, this study encompassed a heterogeneous group of thoracolumbar procedures varying in invasiveness, ranging from discectomy to interbody fusion. Although this allowed for a broad capture of thoracolumbar surgeries, we were unable to stratify risk by specific procedure type or instrumentation due to limitations of the database. Future studies with more granular data may address procedure-specific risks. Furthermore, the PearlDiver database lacks physiologic or laboratory data (e.g., thrombocytosis, D-dimer levels) or clinical mobility status (e.g., bed rest), which are established contributors to thrombotic risk. This limits the ability to control for these important covariates. Despite these limitations, our cohort’s composition helped achieve this study’s goals, which were to establish broad changes in thrombotic complications in the post-COVID era. Future research should incorporate EMR-linked databases with laboratory values, medication data, and mobility measures. Prospective studies may help identify persistent biomarkers of hypercoagulability in patients with prior COVID-19 undergoing elective spine surgery.

Thrombotic complications appear to be increased among patients undergoing thoracolumbar spine surgery in the post-COVID era. A history of COVID-19–related hospitalization was the strongest predictor of risk, while the influence of preoperative vaccination remains uncertain and warrants further investigation.