Abstract
Introduction
Spinal fusion is an operation that is employed to treat spinal diseases. Surgical site infection (SSI) after lumbar fusion (LF) is a postoperative complication. SSI is treated with irrigation and debridement (I&D), which requires readmittance following discharge or prolonged hospital stays, which are deleterious to patients' mental health. The long-term relationship between treating SSI with I&D and patients' mental health is still understudied.
Methods
Using the Mariner dataset from the PearlDiver Patient Records Database using Current Procedural Terminology and International Classification of Diseases procedure codes, retrospective cohort analysis was carried out. This study involved 445,480 patients who underwent LF with at least 2-year follow-up and were followed up for 2 years. Of the patients, 2,762 underwent I&D. Using univariate analysis employing Pearson Chi-square and Student t-test, where appropriate (Table 1), patient demographics between cohorts were gathered. 2-year cumulative incidence (CI) between LF and I&D cohorts was calculated using Kaplan-Meier analysis (Fig. 1, 2, 3). Cox proportional hazards were employed to observe significant differences in CI rates (Table 2).
Results
For patients who received I&D, 2-year CI depression (HR: 1.72; 95% CI: 1.49-1.99; P<0.001) and stress (HR: 1.35; 95% CI: 1.02-1.79; P=0.035) rates were significantly higher than for those who did not. There was no statistically significant difference in 2-year CI anxiety rates between cohorts (HR: 0.92; 95% CI: 0.58-1.46; P=0.719).
Conclusions
In conclusion, 16.8% of patients developed new-onset depression 2 years following I&D, in comparison to 10.3% of those who underwent LF. Patients who underwent I&D following LF were significantly more likely to experience depression and stress. To mitigate negative mental health outcomes, mental health services should be available to patients who underwent surgery.
Keywords: Lumbar fusion, mental health, irrigation and debridement, surgical site infection, postoperative outcomes
Introduction
Spinal fusion surgery is a common operation for treating spinal deformities, vertebral fractures, degenerative discs, and instability, with an estimated 400,000 procedures being performed each year in the United States1). Surgical site infection (SSI) following lumbar fusion (LF) surgery is a not uncommon difficult postoperative complication that presents challenges to patients and healthcare providers due to associated high rates of morbidity and mortality and increase in healthcare costs2). SSIs are due to a combination of several factors, which include incision site infections, prolonged exposure of the body cavity to open air, and the use of instrumentation utilized to stabilize the spine. For LFs, the latter is a leading cause of SSIs owing to the need for stabilization of the affected spinal area. Bacteria can adhere, proliferate, and spread from the instrumentation, potentially leading to sepsis, multi-organ failure, and death3).
In the United States, SSIs account for 1% of postoperative complications and 20% of nosocomial infections. An estimated 8,000 people die per year from SSIs, which presents an urgent need for action4). The incidence of SSI following LF remains troublingly high. Such SSIs are estimated to add 11 extra postoperative days to the hospital stay and result in a 20% incidence of readmittance for associated complications in comparison to those who do not contract an SSI1). SSIs often occur early in the postoperative period, incurring additional time and cost to patients and their families in the hospital while delaying or complicating recovery of spinal function2).
The standard of treatment for SSI is irrigation and debridement (I&D), a highly effective procedure that removes the infection from the surgical site. Retaining the instrumentation while balancing antibiotic use is still the priority of I&D procedures since premature removal of stabilizing instrumentation can lead to premature spinal arthritis and instability5). This procedure necessitates either readmittance following discharge or prolonged hospital stays for patients who present with early postoperative signs of infection.
Prolonged hospital stays and readmittance due to SSIs are deleterious to a patient's mental health, with previous studies reporting that long hospital stays can lead to increased feelings of depression, anxiety, isolation, and shame6). Some data outline the short-term effects of prolonged hospital stays, but what remains unclear is the long-term relationship between treating SSI with I&D and a patient's mental health.
Materials and Methods
Database
Using the Mariner dataset from the PearlDiver Patient Records Database (www.pearldiverinc.com), a retrospective cohort analysis was conducted. The Mariner dataset contains all payer's claims information of more than 157 million patients from January 2010 to October 2021. Mariner provides longitudinal follow-up employing unique patient identifier codes that are not limited to changes in insurance status, thus minimizing loss to follow-up in the system. Moreover, it provides only de-identified information to users, which exempts this study from Institutional Review Board approval.
Patient population
Patients who underwent primary LF were identified using Current Procedural Terminology (CPT) and International Classification of Diseases (ICD) procedure codes (Supplementary Table 1). Patients were included if they underwent lumbar fusion (LF) with at least a 2-year follow-up and were followed for a maximum of 2 years. By reviewing patient records for continued coverage for at least 2 years, a 2-year follow-up was confirmed in the Mariner dataset. Those who were not included were assumed to be lost to follow-up. Those who had a prior history of depression, stress, anxiety, bipolar disorder, or psychotic disorders were excluded using ICD-9 and ICD-10 codes (Supplementary Table 1). Following these criteria, patients were stratified into those who later underwent I&D (I&D cohort) and those who did not (LF cohort). Using the CPT code 22015, I&D was determined. Fig. 1 shows the inclusion and exclusion criteria. In total, 445,480 patients who underwent lumbar fusion were included in this study. Of them, 2,762 underwent I&D and 442,718 did not.
Figure 1.
Flow diagram showing exclusion and inclusion criteria.
Demographic, comorbidities, and outcome variables
Demographic characteristics included age, gender, and Charlson Comorbidity Index (CCI). The primary outcome was the 2-year cumulative incidence (CI) of mental health outcomes including depression, stress, and anxiety (Supplementary Table 1).
Propensity score matching
Propensity score matching was conducted between patients who underwent I&D and those who did not in order to control for measured covariates and mitigate potential confounders. The propensity score was defined as the conditional probability of having undergone LF based on age, gender, CCI, smoking status, and obesity status. Matching was conducted using a 1:1 nearest-neighbor matching ratio using univariate analysis. Propensity score matching was performed using R Software (Vienna, Austria) provided by the PearlDiver database. Following matching, 2,756 patients were included in the LF cohort, and 2,756 patients were included in the I&D cohort. Table 1 shows the demographic and comorbidity information for both cohorts.
Table 1.
Demographic and Comorbidity Characteristics of Lumbar Fusion and Irrigation and Debridement Cohorts Following Matching.
| Lumbar fusion | Irrigation and debridement | P-Value | |||
|---|---|---|---|---|---|
| n | % | n | % | ||
| Total | 2,756 | - | 2,756 | - | - |
| Age ( years ) | 60.7±13.6 | - | 60.7±13.5 | - | 0.929 |
| <50 | 497 | 18.03 | 497 | 18.03% | 1.00 |
| 50-59 | 586 | 21.26 | 586 | 21.26% | 1.00 |
| 60-69 | 796 | 28.88 | 796 | 28.88% | 1.00 |
| 70-74 | 603 | 21.88 | 603 | 21.88% | 1.00 |
| 75+ | 274 | 9.94 | 274 | 9.94% | 1.00 |
| Gender | - | - | - | - | - |
| Male | 1,211 | 43.9 | 1,211 | 43.9% | 1.00 |
| Female | 1,545 | 56.1 | 1,545 | 56.1% | 1.00 |
| Charlson Comorbidity Index | 1.75±2.22 | - | 1.75±2.22 | - | 1.00 |
| 0 | 933 | 33.85 | 933 | 33.85% | 1.00 |
| 1 | 715 | 25.94 | 715 | 25.94% | 1.00 |
| 2 | 434 | 15.75 | 434 | 15.75% | 1.00 |
| 3+ | 674 | 24.46 | 674 | 24.46% | 1.00 |
| Smoking | 136 | 4.93 | 136 | 4.93% | 1.00 |
| Obesity | 247 | 8.96 | 247 | 8.96% | 1.00 |
Statistical analysis
Patient demographics between the two cohorts were conducted using univariate analysis employing Pearson Chi-square and Student t-test analysis, where appropriate. These results were recorded as the number of patients in each category, the incidence/prevalence rate (%), and the p-value. The 2-year CI between the LF and I&D cohorts was performed using Kaplan-Meier analysis. Cox proportional hazard model was employed to observe significant differences in the cumulative incidence rates with the output recorded as the hazard ratios (HRs), 95% confidence intervals (95% CIs), and p-value. For this study, a p-value of less than 0.05 was used as the significance level. All statistical analysis was conducted using R software (Vienna, Austria) provided by the PearlDiver database.
Results
Cumulative incidence for depression
The 6-month, 1-year, and 2-year CI of depression for those who underwent I&D was 9.3%, 12.1%, and 16.8%, respectively (Fig. 2). For the LF cohort, the 6-month, 1-year, and 2-year CI for depression was 3.6%, 6.0%, and 10.3%, respectively (Fig. 2). Compared to those who did not receive I&D, the 2-year cumulative incidence rate of depression was significantly higher for patients who did receive this procedure (HR: 1.72; 95% CI: 1.49-1.99; p<0.001; Table 2).
Figure 2.
Cumulative incidence of depression for patients in the lumbar fusion and irrigation and debridement cohorts.
Table 2.
Cox Proportional Hazards Analysis of 2-Year Mental Health Outcomes for Matched Lumbar Fusion Versus Irrigation and Debridement Cohorts.
| Outcome | Hazard ratio | 95% Confidence interval | P - Value |
|---|---|---|---|
| 2- Year mental health outcomes | |||
| Depression | 1.72 | 1.49-1.99 | <0.001 |
| Stress | 1.35 | 1.02-1.79 | 0.035 |
| Anxiety | 0.92 | 0.58-1.46 | 0.719 |
Cumulative incidence for stress
The 6-month, 1-year, and 2-year CI of stress disorders for those who underwent I&D was 2.6%, 3.0%, and 4.2%, respectively (Fig. 2). For the LF cohort, the 6-month, 1-year, and 2-year CI for stress disorders was 1.2%, 1.7%, and 3.1%, respectively (Fig. 2). Compared to those who did not receive I&D, the 2-year cumulative incidence rate of stress disorders was significantly higher for patients who did receive this procedure (HR: 1.35; 95% CI: 1.02-1.79; p=0.035; Table 2).
Cumulative incidence for anxiety
The 6-month, 1-year, and 2-year CI of anxiety disorders for those who underwent I&D was 0.4%, 0.9%, and 1.2%, respectively (Fig. 4). For the LF cohort, the 6-month, 1-year, and 2-year CI for anxiety disorders was 0.6%, 0.9%, and 1.3%, respectively (Fig. 4). No statistically significant difference was found in the 2-year cumulative incidence rate of anxiety disorders between patients who did or did not receive I&D following LF (HR: 0.92; 95% CI: 0.58-1.46; p=0.719; Table 2).
Figure 4.
Cumulative incidence of anxiety disorders for patients in the lumbar fusion and irrigation and debridement cohorts.
Figure 3.
Cumulative incidence of stress disorders for patients in the lumbar fusion and irrigation and debridement cohorts.
Discussion
In inpatients who underwent LF, I&D following SSI has been shown to contribute to poor mental health outcomes. This study is the first to show 2-year postoperative mental health outcomes after I&D for SSIs post LF in a nationwide sample of patients. The incidence of SSI following LF is estimated to be between 0.3% and 9%; so, this study is consistent with the literature findings7). We found that patients undergoing I&D following LF are at a significantly increased risk of developing depression and stress disorders when compared to those who are undergoing a LF without complications requiring an I&D. No significant increase in anxiety disorders was found in patients who underwent I&D.
Depression
The National Institute of Mental Health reported that 21 million Americans suffered from a major depressive episode between 2018 and 2020, with the prevalence of these episodes in females exceeding that of males8). Among the patient cohort, 16.8% of participants developed new-onset depression 2 years following I&D in comparison to 10.3% for those who solely underwent LF. These data are consistent with that of prior studies that investigate mental health disorders in surgical patients. A longitudinal study using health data from 1995 to 2010 from the California OSHPD longitudinal inpatient discharge administrative database reported that those who underwent spine surgery had an adjusted hazard ratio for depression of 5.05 when compared to those who did not undergo surgery9). Additionally, SSIs are associated with increased hospital readmissions and subsequent depressive episodes9). Gold et al. examined rates of readmission and rates of depression among patients who underwent total joint arthroplasty (TJA) and found that those who were readmitted had a 21%-24% increased odds of depression10). Rates of depression among patients who undergo surgery, in general, are also similar to this study. A study of patients undergoing cardiothoracic surgical resection of lung cancer had a depression rate of 19.4%7). Several factors can contribute to increased risks of depression in patients undergoing orthopedic surgery including postoperative immobility, pain, and complications that delay patient discharge11). Thus, our data are reasonably consistent with those of previous studies that measured mental health changes following orthopedic surgery.
Stress and anxiety
Since 2020, 49% of adult Americans self-report experiencing stress that negatively affects their lives12). In this study, stress was defined as post-traumatic stress disorder, acute stress reaction, and adjustment disorder. Approximately 4% of patients develop new-onset stress disorders 2 years post I&D in comparison to 3.1% of those who solely underwent LF. Compared to those who did not receive I&D, these patients had a hazard ratio of 1.35, which indicates an increased risk of developing a stress-related disorder. These data are consistent with previous studies that examined post-traumatic stress disorder (PTSD) in surgical patients. Archer et al. examined clinical pain and PTSD outcomes following orthopedic reconstruction for traumatic events and found that patients were 1.4 times more likely to experience PTSD if they underwent operative intervention13).
Approximately 31.1% of Americans experience anxiety in their lives, and 19.1% of American adults experienced anxiety within the last year14). Anxiety following surgery is a common phenomenon, with patients reporting pain, dissatisfaction with results, and diminished functional capacity. Nevertheless, this study suggests that having to undergo I&D for SSI does not significantly affect a patient's anxiety ratings. In 2021, Götz et al. found that 9.5% of patients who underwent TJA were very or extremely anxious. Despite stress and anxiety often coexisting in patients who undergo spine surgery, this study does not suggest an increase in anxiety due to LF15). This can be attributed to ICD codes not being sufficient at capturing all patients with anxiety as well as patient hesitance with sharing their mental health status due to stigma. Although not statistically significant, this study still shows a 1.3% increased rate of anxiety following surgery, and it is possible that our small sample size was unable to include an adequate number of patients who truly had the disorder, as well as those who were hesitant to disclose their mental health status.
Patient care improvements
Healthcare providers prioritize patient mental health outcome improvement. Undergoing surgery can result in various postoperative complications, which include pain, immobility, surgical site infections, and venous thromboembolism, which are all predictors of depression. The Medicare Accountable Care Organization recommends screening patients preoperatively and postoperatively for depression as well as consolidating medications patients are prescribed10). This will allow patients and surgeons the opportunity to discuss the timing of their operation so that patients do not undergo surgery in a depressive state, which can further worsen postoperative depression. To address mental health concerns before and after surgical intervention, they further advocate for a more interdisciplinary approach in which primary care and mental health providers are added to a patient's team.
Appropriate pain management must be provided to patients on an individual basis to ensure that they are satisfied with their postoperative care16). Waelkens et al. demonstrated that intraoperative use of paracetamol, cyclo-oxygenase 2-specific inhibitors, or nonsteroidal anti-inflammatory drugs were successful at mitigating patient pain; moreover, intraoperative intravenous administration of low-dose ketamine was appropriate17). In the postoperative setting, rescue analgesia with opioids is recommended for appropriate pain management. Additional recommendations for improving patient pain include opting for a minimally invasive approach to the procedure and early mobilization and ambulation following LF surgery18).
Strengths and limitations
Since this study utilized a national patient database, we were able to gather patient data from across the United States, making the results more generalizable to the broader population when compared to single-institution studies. Furthermore, we were able to examine a large patient cohort and include data from long-term follow-up. Nevertheless, the results of this study should be viewed in the context of its limitations. Moreover, considering that this study utilized ICD-9 and ICD-10 codes, there is an opportunity for miscoding, which can fail to include patients who did suffer from mental health disorders but were not properly entered into the system. Furthermore, not all patients who underwent LF were likely screened for mental health disorders. A larger sample size could have been obtained with fewer patients lost to follow-up. Furthermore, since these data included patients who underwent surgery during the COVID-19 pandemic, there can be an overestimation of the number of patients with mental illness included, given the pandemic's exacerbation of mental health disorders. COVID-19 may have exacerbated patients' mental health concerns, but there was also a decrease in the rate of elective surgeries, thus further skewing these data. Despite these limitations, considering the results of our study, additional research is indicated to further study this concerning incidence of depression and stress in the face of SSI.
Conflicts of Interest: The authors declare that there are no relevant conflicts of interest.
Sources of Funding: None
Author Contributions: Matthew Walker wrote the manuscript; Philip Parel wrote Pearl Diver code; Alisa Malyavko and Amy Zhao provided edits to the manuscript; Theodore Quan, Caillin Marquardt, Addisu Mesfin, and Tushar Patel finalized the manuscript.
Ethical Approval: Ethical approval was waived by the ethics committee due to the retrospective study design.
Informed Consent: Consent was not required because this study involved no human subject.
Supplementary Material
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