Abstract
Introduction
Anterior cervical discectomy and fusion (ACDF) is a commonly performed procedure for the treatment of degenerative cervical disease. With continued increase in U.S. healthcare expenditure, surgeons have begun to more closely examine the benefits of performing ACDF in an outpatient setting to increase efficiency, reduce the overall financial burden on patients/providers, and provide streamlined care for these patients. The purpose of this study was to analyze outcomes following outpatient ACDF for the treatment of myelopathy.
Methods
14,490 patients who had undergone ACDF for myelopathy from 2010 to 2018 were included in this retrospective study, of which 2956 (20.40%) patients were considered to have undergone outpatient surgery. Pearson chi-squared tests and Fischer’s Exact Tests were used to analyze differences in categorical variables of demographics, preoperative comorbidities, and postoperative complications, while Mann-Whitney-U-Tests were used to compare mean values of continuous variables. Coarsened-exact-matching (CEM) was implemented to control for baseline differences in demographics and comorbidities, and post-matching diagnostics included multivariate and univariate imbalance measure assessment. Outcomes were compared between the CEM-matched inpatient and outpatients ACDF cohorts.
Results
Upon CEM-matching (L1-statistic <0.001), the outpatient cohort (n = 2610, 25.13%) demonstrated significantly lower rates of any complication (p < 0.001), minor complications (p = 0.001), urinary tract infections (p = 0.029), blood transfusions (p < 0.001), major complications (p < 0.001), deep incisional surgical site infections (p = 0.017), ventilator dependence (p = 0.027), cardiac arrest (p = 0.028), unplanned reoperations (p = 0.001), and mortality (p = 0.006) in the 30-day postoperative period when compared to inpatient controls (n = 7774, 74.87%).
Conclusion
ACDF has been a target amongst spinal procedures as a prime candidate for outpatient surgery. However, no previous reports have described complication rates and perioperative parameters in the sub-population of outpatient ACDF patients with myelopathy. In addition to shorter times from admission to operating room, operative time, and LOS, our study also demonstrated lower rates of major and overall complications in outpatient ACDF’s for myelopathy in comparison to their inpatient counterparts. Performing ACDF’s for myelopathy in an outpatient setting may help to curb costs, improve outcomes, and serve as a valuable learning resource for graduate medical education with rapid turnovers and shorter operative times.
Keywords: Myelopathy, Anterior cervical discectomy and fusion, ACDF, Complications, Inpatient, Outpatient
1. Introduction
Anterior cervical discectomy and fusion (ACDF) is a widely utilized procedure for operative management of various cervical spine pathologies when conservative treatment options are unsuccessful at alleviating symptoms.1 The number of cervical spine procedures to treat degenerative conditions is expected to increase as the population ages.2,3 As healthcare expenditures continue to climb, institutions are seeking ways to decrease expenses without compromising patient care. Performing cases in outpatient ambulatory surgical centers (ASCs) is one way of potentially decreasing total costs when compared to inpatient hospital procedures.4 As a result, there is increasing interest in comparing outcomes of the procedures performed in outpatient versus inpatient settings.
Previous literature has compared costs, complication rates, and operative time of various orthopaedic procedures done in the ASC and inpatient setting.4 Although complication rates following ACDF in the ASC versus inpatient setting have been previously examined,4 comparisons of peri-operative/operative parameters and complication rates have not been examined based on setting for ACDF done for myelopathy. To the author’s knowledge, there is a paucity of literature examining outcomes for ACDF due to myelopathy in the inpatient and outpatient settings. Therefore, the primary objective of this study was to compare the complication rates and perioperative/operative parameters in all-level ACDF procedures for the treatment of myelopathy in the outpatient versus inpatient setting to determine whether surgical setting influenced outcomes in the subset population of patients presenting with myelopathy.
2. Materials & Methods
2.1. Patient cohort selection
The American College of Surgeons National Surgical Quality Improvement Program (ACS-NSQIP) Database was queried to identify all patients who had undergone ACDF for the treatment of myelopathy from 2010 to 2018. Patients were isolated by Current Procedure Terminology (CPT) codes, corresponding with 22551 (anterior or anterolateral cervical arthrodesis below C2), 22554 (anterior interbody arthrodesis with minimal discectomy), and 63075 (anterior discectomy). Given that discectomy rarely occurs without fusion, we included 63075, in addition to 22551 and 22554, following a previously published study on ACDF with the same dataset.5 Patients with a postoperative diagnosis of cervical spine myelopathy were subsequently isolated, identified by International Classification of Diseases (ICD)-9 and ICD-10 Codes 721.1, 721.91, 722.70, 722.71, M47.10, M47.12, M47.13, M50.00, M50.01, M50.02, M50.021, M50.022, M50.023, and M50.03. Patients with incomplete demographic and preoperative comorbidity information, as well as those who underwent posterior arthrodesis, laminectomies, facetectomies, and foraminotomies of the cervical vertebral bodies, were excluded from the study. After all inclusion and exclusion criteria were applied, 14,490 ACDF patients with a diagnosis of myelopathy were ultimately included in this retrospective study for analysis. These patients were then stratified into two separate cohorts—inpatient (n = 11534, 79.60%) and outpatient (n = 2956, 20.40%).
2.2. Variables
Demographic factors and preoperative comorbidities were analyzed to better characterize the ACDF patient sample of interest. Demographic factors include age, sex, race, and body mass index (BMI). Preoperative comorbidities include diabetes mellitus, smoking history, chronic obstructive pulmonary disease (COPD), dyspnea, ventilator dependence, ascites, congestive heart failure, hypertension requiring medication management, acute renal failure, dialysis-dependence, disseminated cancer, open wound/wound infections, chronic steroid usage, significant weight loss (>10% of body weight within six months before surgery), hematologic disorders (i.e. Vitamin K deficiency, thrombocytopenia, hemophilias, etc.), preoperative blood transfusions, systemic sepsis, and functional dependence. Perioperative variables such as time of surgical delay from admission to operation, operative time, total length of hospital stay, primary modality of anesthesia, and American Society of Anesthesiologists (ASA) classification were also included. Extended operative times were defined as those greater than the 75th percentile of the entire cohort (x ≥ 171.0 min). The number of levels fused was also calculated by using the CPT code 22552 to indicate the number of additional levels fused and stratified into one-level, two-levels, or three or more level fusions.
Postoperative complications were analyzed individually and as minor and major complications, based on previously published orthopaedic studies.6, 7, 8, 9 Minor complications include superficial surgical site infections (SSI), wound dehiscence, pneumonia, urinary tract infections, progressive renal insufficiency, and blood transfusions. Major complications include deep incisional SSI, organ/space SSI, unplanned intubation, pulmonary embolism (PE), ventilator dependence (≥48 h), acute renal failure, cerebral vascular accidents/strokes, cardiac arresting requiring cardiopulmonary resuscitation, myocardial infarctions, deep venous thromboembolisms (DVT), systemic sepsis, septic shock, unplanned reoperations, unplanned readmission, and mortality within the 30-day period following ACDF for myelopathy.
2.3. Statistical analysis
To determine differences in patient demographic factors, preoperative comorbidities, and perioperative/postoperative outcomes, univariate analyses were first utilized in establishing differences in these variables between the inpatient and outpatient cohorts. Pearson’s Chi-Squared Tests and Fischer’s Exact Tests were implemented in analyzing categorical variables, while Mann-Whitney-U-Tests were used to assess for differences in mean values of continuous variables such as age and time parameters. Continuous variables are expressed as mean values with their respective standard deviations, while categorical variables are reported as a proportion representing incidence rates within the respective cohorts.
Coarsened-exact-matching (CEM) was implemented in matching outpatient cases to inpatient controls to control for baseline differences in demographics and preoperative comorbidities. CEM has been gaining traction in the orthopaedic literature as the superior method of matching, with less statistical assumption and reported model dependence than the commonly used propensity-score method of matching.10, 11, 12 Its use has been validated in large datasets in various surgical procedures.10,13 The CEM algorithm will temporarily coarsen all data to produce exact matches based on the entered variables, eventually dropping non-exact matches to ensure inclusion of only the most similar patients. CEM was used to match on age, BMI, gender, race, diabetes mellitus, smoking history, dyspnea, ventilator dependence, COPD, ascites, CHF, hypertension requiring medication management, acute renal failure, dialysis, disseminated cancer, open wounds/wound infections, chronic steroid use, significant weight loss (>10% of body weight within six-months leading up to surgery), hematologic disorders, preoperative blood transfusions, sepsis, functional dependence, ASA classification, primary anesthetic mechanism, and number of levels. The CEM-matched cohorts of inpatient and outpatient cases were analyzed for differences in complication rates.
All statistical findings with p-values less than or equal to 0.05 were considered significant in this analysis. All statistical analyses were performed using the IBM® SPSS® Statistics Version 25 software (IBM Corporation, Armonk, NY) and R© Version 3.3.3.
3. Results
A total of 14,490 patients with a diagnosis of myelopathy who had undergone ACDF from 2010 to 2018 were included in this study, of which 2956 (20.40%) were outpatient and 11534 (79.60%) were inpatient. In the unmatched comparison, the outpatient cohort was significantly younger (x̄ = 55.13 ± 11.151; p < 0.001) than the inpatient cohort (x̄ = 57.94 ± 11.778). A larger proportion of the outpatient cohort was under 60 years of age (p < 0.001) and self-identified as White/Caucasian (p < 0.001) than the inpatient cohort. While mean BMI was significantly different between the two cohorts (p = 0.036), the distribution of patients by BMI categories was not significant (p = 0.152). Significant differences were also observed in rates of diabetes mellitus (p < 0.001), COPD (p < 0.001), CHF (p = 0.033), hypertension (p < 0.001), dialysis (p < 0.001), open wounds/wound infections (p = 0.018), chronic steroid use (p = 0.004), significant weight loss (p = 0.004), hematologic disorders (p = 0.003), systemic sepsis (p < 0.001), functional dependence (p < 0.001), ASA classification (p < 0.001), and number of levels (p < 0.001; Supplementary Table 1).
Upon CEM-matching, 2610 (25.13%) outpatient and 7774 (74.87%) inpatient cases were successfully matched. In the CEM-matched-cohort comparison, no demographics or comorbidities were significantly different, with the exception of mean age (p = 0.004; Table 1). The multivariate imbalance measure (L1-statistic) and all univariate imbalances had a significance of <0.001, indicating adequate matching with minimal imbalance.
Table 1.
DEMOGRAPHICS & COMORBIDITIES in CEM-Matched Inpatient vs. Outpatient Cohorts.
| Inpatient |
Outpatient |
P-Value | |||
|---|---|---|---|---|---|
| (n = 7774, 74.87%) | (n = 2610, 25.13%) | ||||
| DEMOGRAPHICS | |||||
| Age (Mean ± SD)a | 56.86 ± 11.959 | 56.14 ± 11.461 | 0.004# | ||
| Age Categories (years) | 0.991 | ||||
| x < 60.00 | 4579 | 58.90% | 1537 | 58.89% | |
| x ≥ 60.00 | 3195 | 41.10% | 1073 | 41.11% | |
| Gender | 0.987 | ||||
| Female | 3668 | 47.18% | 1231 | 47.16% | |
| Male | 4106 | 52.82% | 1379 | 52.84% | |
| Race/Ethnicity | 0.999 | ||||
| Asian/Pacific Islander | 90 | 1.16% | 30 | 1.15% | |
| Black/African American | 805 | 10.36% | 270 | 10.34% | |
| White/Caucasian | 6879 | 88.49% | 2310 | 88.51% | |
| Body Mass Index (kg/m2) (Mean ± SD)a | 30.14 ± 6.470 | 30.21 ± 6.471 | 0.270 | ||
| Body Mass Index (kg/m2) | 1.000 | ||||
| Normal | 1520 | 19.55% | 510 | 19.54% | |
| Overweight | 2784 | 35.81% | 935 | 35.82% | |
| Class I Obese | 2031 | 26.13% | 682 | 26.13% | |
| Class II Obese | 882 | 11.35% | 296 | 11.34% | |
| Class III Obese |
557 |
7.16% |
187 |
7.16% |
|
|
PRE-OPERATIVE COMORBIDITIES | |||||
| Diabetes Mellitus | 0.999 | ||||
| No Diabetes Mellitus | 6905 | 88.82% | 2318 | 88.81% | |
| Non-Insulin Dependent | 591 | 7.60% | 198 | 7.59% | |
| Insulin Dependent | 278 | 3.58% | 93 | 3.56% | |
| Smoking History | 1948 | 25.06% | 654 | 25.06% | 1.000 |
| Dyspnea | 115 | 1.48% | 39 | 1.49% | 0.956 |
| Ventilator Dependence | 0 | 0.00% | 0 | 0.00% | - |
| COPD | 80 | 1.03% | 27 | 1.03% | 0.981 |
| Ascites | 0 | 0.00% | 0 | 0.00% | – |
| Congestive Heart Failure | 0 | 0.00% | 0 | 0.00% | – |
| Hypertension | 3839 | 49.38% | 1289 | 49.39% | 0.997 |
| Acute Renal Failure | 0 | 0.00% | 0 | 0.00% | – |
| Dialysis | 0 | 0.00% | 0 | 0.00% | – |
| Disseminated Cancer | 0 | 0.00% | 0 | 0.00% | – |
| Wound Infection | 0 | 0.00% | 0 | 0.00% | – |
| Chronic Steroid Use | 55 | 0.71% | 18 | 0.69% | 0.925 |
| Weight Loss | 0 | 0.00% | 0 | 0.00% | - |
| Bleeding Disorders | 9 | 0.12% | 3 | 0.11% | 1.000 |
| Preoperative Transfusions | 0 | 0.00% | 0 | 0.00% | - |
| Systemic Sepsis | 0 | 0.00% | 0 | 0.00% | - |
| Functional Status | 0.916 | ||||
| Independent | 7757 | 99.78% | 2604 | 99.77% | |
| Partially/Totally Dependent | 17 | 0.22% | 6 | 0.23% | |
∗ Significant with Bonferroni corrected comparison of proportions (p < 0.05).
# Significant on Mann-Whitney-U-Test.
CEM: Coarsened-Exact-Matching; COPD: Chronic obstructive pulmonary disease.
Values expressed as Mean ± Standard Deviation (SD); all other values expressed as (%) and N.
In comparing the CEM-matched cohorts, the outpatient cohort demonstrated significantly shorter mean operative times (x̄ = 115.12 ± 60.836) than the inpatient cohort (x̄ = 149.16 ± 80.627; p < 0.001). The outpatient cohort also demonstrated significantly shorter total length of hospital stay (1.10 days vs. 2.46 days; p < 0.001). A smaller proportion of the outpatient cohort experienced extended operative times (87.20% vs. 70.89%; p < 0.001; Table 2) than the inpatient cohort. No significant differences were observed in the primary anesthetic mechanism, ASA classification (p = 0.989), or number of levels (p = 1.000; Table 2).
Table 2.
PERIOPERATIVE VARIABLES in CEM-Matched Inpatient vs. Outpatient Cohorts.
| Inpatient | Outpatient | ||||
|---|---|---|---|---|---|
| PERIOPERATIVE VARIABLES | (n = 7774, 74.87%) | (n = 2610, 25.13%) | |||
| Operative Time (min) (Mean ± SD)a | 149.16 ± 80.627 | 115.12 ± 60.836 | <0.001# | ||
| Days from Admission to Operation | 0.39 ± 6.306 | 0.06 ± 1.563 | <0.001# | ||
| Total Length of Hospital Stay (Days) | 2.46 ± 6.775 | 1.10 ± 2.236 | <0.001# | ||
| Anesthesia Administered | – | ||||
| General | 7774 | 100.00% | 2610 | 100.00% | |
| Epidural/Spinal | 0 | 0.00% | 0 | 0.00% | |
| Local/Regional | 0 | 0.00% | 0 | 0.00% | |
| MAC/IV Sedation | 0 | 0.00% | 0 | 0.00% | |
| ASA Classification | 0.989 | ||||
| ASA < 3 | 4192 | 53.92% | 1407 | 53.91% | |
| ASA ≥ 3 | 3582 | 46.08% | 1203 | 46.09% | |
| Number of Levels | 1.000 | ||||
| 1 Level | 4224 | 54.33% | 1418 | 54.33% | |
| 2 Levels | 3103 | 39.92% | 1042 | 39.92% | |
| ≥3 Levels | 447 | 5.75% | 150 | 5.75% | |
| Extended Operative Time (75th Percentile) | <0.001 | ||||
| x < 171.0 min. | 5511 | 70.89% | 2276 | 87.20% | ∗ |
| x ≥ 171.0 min. | 2263 | 29.11% | 334 | 12.80% | ∗ |
∗ Significant with Bonferroni corrected comparison of proportions (p < 0.05).
# Significant on Mann-Whitney-U-Test.
CEM: Coarsened-Exact-Matching; MAC: Monitored Anesthesia Care; IV: Intravenous; ASA: American Society of Anesthesiologists.
Values expressed as Mean ± Standard Deviation (SD); all other values expressed as (%) and N.
Upon CEM-matching, postoperative complication rates were analyzed for differences between the two matched cohorts. The outpatient cohort demonstrated significantly lower rates of any complication (p < 0.001), minor complications (p = 0.001), urinary tract infections (p = 0.029), blood transfusions (p < 0.001), major complications (p < 0.001), deep incisional surgical site infections (p = 0.017), ventilator dependence (p = 0.027), cardiac arrest (p = 0.028), unplanned reoperations (p = 0.001), and mortality (p = 0.006) in the 30-day postoperative period when compared to inpatient controls (Table 3).
Table 3.
Postoperative Complication Rates in CEM-Matched Inpatient vs. Outpatient Cohorts.
| POSTOPERATIVE COMPLICATIONS | Inpatient (n = 7774) | Outpatient (n = 2610) | P-Value | ||
|---|---|---|---|---|---|
| Any Complication | 520 | 6.69% | 92 | 3.52% | <0.001∗ |
| Minor Complication | 161 | 2.07% | 27 | 1.03% | 0.001∗ |
| Superficial Incisional SSI | 20 | 0.26% | 6 | 0.23% | 0.809 |
| Wound Disruption | 10 | 0.13% | 0 | 0.00% | 0.075 |
| Pneumonia | 51 | 0.66% | 14 | 0.54% | 0.503 |
| Urinary Tract Infection | 49 | 0.63% | 7 | 0.27% | 0.029∗ |
| Progressive Renal Insufficiency | 1 | 0.01% | 0 | 0.00% | 1.000 |
| Blood Transfusions | 42 | 0.54% | 0 | 0.00% | <0.001∗ |
| Major Complication | 435 | 5.60% | 85 | 3.26% | <0.001∗ |
| Deep Incisional SSI | 15 | 0.19% | 0 | 0.00% | 0.017∗ |
| Organ/Space SSI | 9 | 0.12% | 0 | 0.00% | 0.124 |
| Unplanned Intubation | 54 | 0.69% | 10 | 0.38% | 0.079 |
| Pulmonary Embolism | 22 | 0.28% | 11 | 0.42% | 0.277 |
| Ventilator Dependence (>48 h) | 36 | 0.46% | 4 | 0.15% | 0.027∗ |
| Acute Renal Failure | 2 | 0.03% | 3 | 0.11% | 0.105 |
| CVA/Stroke | 10 | 0.13% | 0 | 0.00% | 0.067 |
| Cardiac Arrest | 14 | 0.18% | 0 | 0.00% | 0.028∗ |
| Myocardial Infarction | 12 | 0.15% | 7 | 0.27% | 0.287 |
| DVT | 27 | 0.35% | 4 | 0.15% | 0.116 |
| Systemic Sepsis | 19 | 0.24% | 4 | 0.15% | 0.391 |
| Septic Shock | 11 | 0.14% | 6 | 0.23% | 0.399 |
| Unplanned Reoperation | 165 | 2.12% | 29 | 1.11% | 0.001∗ |
| Unplanned Readmission | 266 | 3.42% | 70 | 2.68% | 0.065 |
| Death | 19 | 0.24% | 0 | 0.00% | 0.006∗ |
∗ Significant with Bonferroni corrected comparison of proportions (p < 0.05).
CEM: Coarsened-exact-match; SSI: Surgical Site Infection; CVA: Cerebral Vascular Accident; DVT: Deep Venous Thromboembolism.
4. Discussion
As the financial implications of healthcare in the United States continue to concern patients and providers alike, the adoption of value-based healthcare practices with aims to reduce associated costs has been garnering increasing attention in orthopaedic surgery.4,14 In an era of escalating healthcare expenditure, the reduction in total associated costs for outpatient ACDFs has been explored as a prime candidate to mitigate financial burden. One study by Purger et al. had reported a cost-difference of almost $10,000 ($9479 for outpatient vs. $19,465 for inpatient) between inpatient and outpatient ACDF’s.15 With a reported overall cost reduction of approximately 30% when performed in an outpatient setting,14,16 Cost-benefit analyses have favored outpatient ACDF’s with a reported overall cost reduction of approximately 30%.14,16 The touted advantages of outpatient ACDF are extensive. A recent meta-analysis reported a comparable safety profile to its inpatient counterparts with similar rates of complications, readmissions, and mortality.16 Currently, ACDF’s can be performed safely on an outpatient basis for proper indications with time to discharge averaging under 48 h,17 and as quick as under 24 h.18, 19, 20, 21, 22, 23 Readmission rates following outpatient ACDF are also low, with some studies demonstrating readmission rates as low as 0%.17,18,24,25 More recently, studies have shown favorable outcomes in the outpatient setting for multi-level ACDF’s with similar outcomes and no associated increased risk of complications when compared to inpatient ACDF’s.16,26 Indeed, Fu et al. report increased complication rates following inpatient one-and-two level ACDF’s when compared to outpatient counterparts. One may postulate that the increased complication rates relates to the inpatient population having higher rates of comorbidities.27 As such, proper patient selection for operative intervention in the ASC is paramount– compared to other spinal procedures, ACDF is a relatively quick procedure, with minimal exposure compared to large spinal deformities that does not require the assistance of a general surgeon to access the spine.
Pierce et al. report extended LOS in patients with a primary diagnosis of myelopathy compared to those with radiculopathy/myeloradiculopathy even after controlling for the degree of invasiveness of the various interventions.28 In light of these results, the authors emphasize that the increased risk for extended LOS in patients with myelopathy should be considered with regards to admission status for these patients in an increasingly cost-conscious healthcare system.28 Although patients with myelopathy were not shown to have extended length of hospital stay in the present study, surgeons should remain aware of these potential risks. However, the findings of this study indicate that patients with myelopathy are likely to experience comparable outcomes following outpatient ACDF. This indicates that the adoption of outpatient ACDF in properly selected myelopathic patients is reasonable.
The present study demonstrated significant reductions in numerous time parameters, such as total operative time, time from hospital admission to operation, and total LOS associated with outpatient ACDF’s in patients with myelopathy compared to inpatient ACDF’s for the same indication. These results are in line with the current literature as multiple studies have reported reductions in operative time for outpatient ACDF’s when compared to inpatient ACDF’s.4,22 With these reductions in time, several interesting implications arise. In a previous analysis of the ACS-NSQIP database, Iweala et al. reports decreased overall costs for various orthopaedic procedures, including ACDF, done in the ASC based on a cost per minute estimate as a result of decreased time in the operating room.4,29 In a retrospective analysis of the Pearl Diver database, Martin et al. also reports lower mean 90-day costs for outpatient ACDF’s ($39,528) compared to inpatients ACDF’s ($47,330) with a narrowing, yet still significant, difference in costs from 2008 to 2014 ($13,745 to $3834).30 Although cost savings were not directly analyzed in the present study, it can be inferred that ACDF for the treatment of myelopathy in the outpatient setting can actually help to curb healthcare costs as the consistent decreases in multiple time parameters in the outpatient setting have been previously reported with cost savings. Future work may seek to quantify just how much savings result by performing ACDF in the ASC for specific indications including, but not limited to, cervical stenosis/myelopathy, post-laminectomy kyphosis, and even vertebral body malignancies.
Furthermore, these reductions in time pose an interesting implication for surgeon outcomes and graduate medical education (GME). Previous reports in the literature demonstrate a relationship between greater surgical volume and decreased complication rates for both ACDF and spinal procedures overall.31,32 In a survey study of orthopaedic surgical resident perspectives on case minimums and preparation for post-residency practice, spinal cases were among the most frequently cited as needing more experience with as the volume of cases were less than other orthopaedic surgical procedures.33 The present study demonstrated significant reductions in both admission to operation time and operation time of ACDF performed for myelopathy. As such, utilizing the ASC setting for ACDF’s may not only cut institutional costs, but it can also serve as a powerful tool for GME by potentially increasing spine case volumes. This paper shows the efficacy and improved quality of ACDFs on an outpatient basis. Given that an increasing number of these ACDFs are being performed at ASCs, GME offices at residencies may consider investing in programs that send their residents to these ASCs which are poised to experience an increasing amount of volume.17 However, furthering the education of residents in training must be carefully weighed with a potential increase in complication rates with more inexperienced resident surgeons.
The present study demonstrated significantly lower rates of any complication overall and major complications following ACDF’s performed in the outpatient setting compared to the inpatient setting myelopathic patients. Generally, operative interventions for patients with higher risk of complications and adverse events are done in the inpatient setting where there are appropriate staff and resources to respond promptly. As a result, a disproportionate number of patients with less comorbidities/lower surgical risk may be obtaining their care at ASC’s. While the current study utilized CEM-matching to control for baseline differences in demographics and comorbidities, the variables provided by the ACS-NSQIP database do not capture the entirety of each patient’s medical history – this represents a limitation in the granularity of information provided by large-sample datasets. As such, the lower complication rates seen with outpatient cases could be explained by patient selection rather than the outpatient setting.
These present results are in line with the current literature, as outpatient ACDF’s have generally been associated with lower complication rates. In a retrospective analysis of the NSQIP database, Fu et al. reports decreased complication rates in outpatient one-two level ACDF’s for all indications compared to those done as inpatient after controlling for preoperative demographics/comorbidities.27 After CEM-matching to control for differences in the outpatient and inpatient cohorts, McClelland et al. report decreased rates of durotomy, paraplegia, infection, and transfusion in the outpatient cohorts following one-two level ACDF’s.16 Similarly, Khalid et al. and Martin et al. also report lower complication rates in outpatient ACDF’s. However, these studies did not control for preoperative comorbidities/demographics, and the decreased complication rates may be attributed to the better overall health status of the outpatient cohort patients.17,30 Other studies and systematic reviews of the literature also report decreased complication rates for ACDF’s in the outpatient setting as well.4,26,34 Our study further supports the existing body of literature on the complication rates/short-term outcomes of ambulatory ACDF in patients with myelopathy.
However, in contrast to the present study and other aforementioned reports, Arshi et al. demonstrate increased rates of postoperative acute renal failure and revision surgeries at six months and one year postoperatively for outpatient ACDF’s after controlling for patient demographics/comorbidities.14 The association between revision needs for index ACDF procedures performed in the outpatient setting is not yet completely understood.14 While unplanned reoperations within the 30-day postoperative period are reported by the ACS-NSQIP database, revision needs beyond this period are not tracked by the ACS-NSQIP database. The long-term patient reported outcome measures (i.e. NDI, VAS scores) specific to cervical spine surgery patients that numerically characterize functional and neurological assessments are also not reported.35 Given these limitations, the present study is unable to provide further analysis on revision rates, necessitated by long-term medical or surgical complications, between outpatient versus inpatient ACDF for the treatment of myelopathy. Future work may be warranted to better elucidate the effects of outpatient surgery on long term patient reported outcomes and revision needs in this subset patient population for ACDF. Prospectively defining the safety profile of outpatient ACDF in patients presenting with myelopathy may better assist surgeons when risk-stratifying patients to identify viable candidates for ACDF in an outpatient setting.
The present study is not without limitations. Inherent to all retrospective studies of similar nature, inaccuracies in data collection and inputting may have posed confounding effects on subsequent analyses. In addition, only patients with complete information regarding the variables of interest were included in the current study; any patients with missing data for the included variables were ultimately excluded. By eliminating patients without complete information, bias may have been introduced. However, the inclusion of cases with missing data could exert greater confounding effects than the exclusion of such data. Furthermore, while this study utilized CPT and ICD codes to isolate ACDF patients with a postoperative diagnosis of myelopathy, CPT codes were initially designed for insurance claims and reimbursement purposes. As such, coding biases motivated by financial incentives may have also been present.35 Another limitation of this study is that there are multiple etiologies of myelopathy that are not recorded in the ACS-NSQIP database. Myelopathy may arise secondary to kyphosis, degenerative spondylolisthesis, osteophytes secondary to degenerative disc disease, or posterior disc herniations that narrow the cervical spinal canal. As each underlying pathology represents a different mechanism of disease, there may be confounding variables that this study could not account for when examining the outpatient versus inpatient cohorts. Finally, the lack of myelopathy-specific (i.e. modified Japanese Orthopaedic Association [mJOA]) and cervical spine surgery-specific (i.e. neck disability index (NDI), Visual Analogue Scale (VAS) pain scores in the neck and/or arms) patient reported outcomes to monitor both the severity of myelopathy and the clinical progression of each patient presents as a limitation. Nonetheless, given the comparable short-term complication rates seen in outpatient procedures to their inpatient counterparts, the authors feel that ACDF may be safely performed in an outpatient setting in patients presenting with myelopathy.
5. Conclusion
With increasing pressures on institutions and surgeons to curb healthcare associated costs, performing procedures in the outpatient setting has been increasingly popular. ACDF has particularly been a target amongst spinal procedures as a prime candidate for the outpatient setting. However, no previous reports have described complication rates and perioperative parameters in the subset ACDF patient population with myelopathy. In addition to shorter times from admission to operating room, operative time, and LOS, our study also demonstrated lower rates of major and overall complications in outpatient ACDF’s for myelopathy when compared to their inpatient counterparts. Performing ACDF’s for myelopathy in an outpatient setting may help to curb costs, maintain favorable outcomes, and serve as a valuable learning resource for graduate medical education with rapid turnovers and shorter operative times.
CRediT authorship contribution statement
Ryan Lee: Conceptualization, Methodology, Formal analysis, Investigation, Writing - original draft. Danny Lee: Conceptualization, Methodology, Formal analysis, Investigation, Writing - original draft. Uchechi Iweala: Investigation, Writing - original draft, Project administration. Pradip Ramamurti: Investigation, Methodology, Writing - original draft. Jeffrey H. Weinreb: Investigation, Writing - original draft, Project administration. Joseph R. O’Brien: Investigation, Writing - original draft, Project administration, Supervision.
Declaration of competing interest
None.
Acknowledgements
None.
Footnotes
Supplementary data to this article can be found online at https://doi.org/10.1016/j.jcot.2020.07.030.
Appendix A. Supplementary data
The following is the Supplementary data to this article:
References
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