Although the post-COVID cohort contained predominantly sicker patients who underwent more rigorous perioperative optimization and experienced more postoperative complications, it is important to note that the higher incidence of postoperative complications observed in the post-COVID SSI cohort, when compared to the pre-COVID SSI cohort, was not correlated with the presence of COVID-19 infection.

Querying the American College of Surgeons National Surgical Quality Improvement Program (ACS NSQIP) database, Momtaz et al conducted a retrospective analysis of 146,430 elderly patients who underwent elective orthopaedic procedures before (n = 94,289) and during (n = 52,141) the pandemic, respectively. Compared to the pre-COVID onset period, patients treated during the pandemic had 1.45 times increased likelihood of any complication, with varying relative risk of physiological system complications, including pulmonary (OR 1.76; 95% CI: 1.55-2.46), cardiac (OR 1.51; 95% CI 1.29 -1.78) and renal systems (OR 1.95; 95% CI 1.55 to 2.46).15 Similarly, Zhong et al, in their review of 40,986 patients from the Premier Healthcare database, reported increased odds of complications, inpatient readmission, intensive care unit admission, and higher treatment costs in patients undergoing orthopedic surgery during the pandemic compared to before.24 It is difficult to draw absolute conclusions regarding the cause of these complications. However, we observed that our post-COVID onset SSI cohort were more likely to have experienced postoperative complications such as anemia requiring transfusion, hypotension requiring vasopressors, and AKI, alongside higher ASA scores and immunosuppression not related to COVID-19 infection when compared to the pre-COVID SSI cohort. As such, there is a suggestion that the association between postoperative complications, higher ASA status and presence of pharmacologic and/or physiological immunosuppression with the development of an SSI post-COVID could be related to the diminished physiological reserve and deconditioning of many of our surgical patients.

These associations may represent important confounding factors, as both higher ASA status and immunosuppression are independently associated with increased risk of postoperative infection. The higher rates in the post-COVID group could be partly explained by changes in referral patterns and surgical triage during the pandemic, in which more complex and higher-risk patients were prioritized for surgery, while lower-risk elective cases were deferred. This shift in case mix may have contributed to the observed increase in SSI incidence in the post-COVID cohort, in addition to other postoperative complications noted. We hypothesize that this may also be a factor for the observed increase in post-operative hardware damage, hardware infection, and spinal hematoma in our post-COVID onset cohort compared to their pre-COVID onset counterparts.

Additionally, the relationship between preoperative medical optimization, perioperative health status, and postoperative complications is complex and undoubtedly multifaceted. Greater adherence to preoperative Staphylococcus sp decolonization interventions such as nasal iodine and CHG bathing, was noted in the post-COVID onset cohort in accordance with routine standard of care policies2, and pandemic-implemented policies to further optimize patient safety.

Several studies have highlighted the impact of delayed medical care on health outcomes during the pandemic.10, 17, 23 In the early phase of the pandemic, emergency department (ED) visits in the United States decreased by 42% compared to the previous year.11 Subsequent research has indicated that delayed ED presentations during the pandemic for concerns such as acute appendicitis and cholecystitis were associated with higher rates of complications.5, 8, 9, 18, 19 Public health research has also highlighted that fear of contracting COVID-19 was amongst the most common reasons for patients delaying healthcare treatment, ultimately increasing overall morbidity and mortality.4, 20 Our findings possibly support these observations: patients with spinal SSI may have delayed seeking medical care after the onset of the pandemic compared to before, resulting in delays in receiving timely treatment.

Another important consideration is the impact of the pandemic on physical activity levels. Preoperative physical activity levels have been shown to predict postoperative outcomes and the risk of postoperative complications.12 This forms the basis for prehabilitation methods, defined as a set of interventions undertaken prior to surgery to enhance cardiorespiratory fitness, reduce perioperative risk and enhance recovery and outcomes.7 During the COVID-19 pandemic, national isolation protocols, quarantine restrictions, lockdowns, business closures, and reduced social opportunities across the world significantly impacted physical activity levels. In a 2021 review of 66 studies involving 86,981 participants worldwide, Stockwell et al reported a significant decrease in physical activity and an increase in sedentary behavior since the onset of the pandemic.21 Oliveira et al observed similar findings among the elderly population in a systematic review of 25 studies16, while Momtaz et al suggest that these findings, and their probable impact on exacerbation of chronic diseases, may directly contribute to a higher incidence of postoperative complications during the pandemic.15

Our study has several limitations that should be considered. Firstly, our data was collected from the records of a single, level 1 trauma center, one of only two such institutions within a 75-mile radius of the largest metropolitan area in Ohio. This introduces an inherent selection bias towards patients of greater complexity, in an area with high socioeconomic deprivation, potentially limiting the generalizability of our findings to broader populations. Secondly, patient data was collected retrospectively based upon review of existing chart-coded diagnoses. Baseline risks of documentation errors, incomplete information, and coding inaccuracies are excepted limitations of this technique. Additionally, the case mix of patients differed between the pre- and post-COVID cohorts. During the pandemic, surgical triage policies and referral patterns may have led to prioritization of more complex or higher-risk patients for surgery, while lower-risk elective cases were deferred. This shift in case mix could have contributed to the observed increase in postoperative complications and SSI incidence in the post-COVID cohort, potentially confounding direct comparisons between the groups. Lastly, our study did not directly analyze the effects of specific infection control policies implemented during the pandemic on the incidence of SSI. Further investigation into this relationship could provide valuable insight into these policies' effectiveness in preventing SSI and enhancing patient outcomes.

In patients with spinal SSI, those operated on after the onset of the COVID-19 pandemic were more likely to be immunosuppressed and at higher perioperative risk. Greater adherence to preoperative Staphylococcus sp decolonization was observed in the post-COVID onset cohort in accordance with routine standard of care and pandemic-implemented policies to optimize patient safety. Our data suggests that readmission of SSI patients was delayed in the post-COVID onset era, perhaps due to pandemic-implemented isolation policies and subsequent patient hesitancy in seeking SSI treatment.

Importantly, the higher incidence of postoperative complications in patients developing spine related SSI in the post-COVID onset cohort was not correlated with COVID-19 infection, but may have been caused by factors such as patient deconditioning and delayed patient-physician interaction due to societal and health care challenges presented during the pandemic. Future research should focus on optimizing infection prevention protocols tailored to high-risk patient populations, further investigation of the impact of COVID-19 on surgical outcomes, and exploring strategies to mitigate postoperative complications.

Our findings suggest that the higher incidence of surgical site infection (SSI) and postoperative complications observed in spine surgery patients after the onset of the COVID-19 pandemic was not directly attributable to the COVID-19 infection itself. Instead, these outcomes appear to be influenced by confounding factors, including higher ASA grade, greater prevalence of immunosuppression, delayed healthcare-seeking behavior, and pandemic-driven changes in referral and surgical triage that shifted case mix toward higher morbidity, higher-risk patients. Reduced physical activity and patient deconditioning during the pandemic may have further diminished physiological reserve, compounding complication risk.

Clinically, this underscores how systemic disruptions in health care, such as delays in treatment, surgical selection, and poor baseline patient health can indirectly worsen surgical outcomes. Health care systems and surgeons should account for these factors by prioritizing perioperative optimization – including prehabilitation, nasal iodine, and CHG bathing - and timely and equitable access to health care to maximize long-term surgical success.