Introduction
Spine surgery is a relatively common procedure in the United States. One form, spinal fusion, has rapidly increased in prevalence by 220% between 1990 and 2001 [
1]. According to the Agency for Healthcare Research and Quality (AHRQ), approximately 427,000 spinal fusions and 417,000 laminectomy surgeries were performed in the United States in 2013 [
2].
Complications are an unfortunate consequence of surgery and may influence recovery rates, quality of life and healthcare costs [
3]. They may take the form of wound-related, surgical or medical complications [
4]. The National Inpatient Sample showed an overall complication incidence of 13.1% from 1993 to 2002 [
4]. Others have reported variable figures depending on the type of surgery, with cervical spine surgery (8.9%) exhibiting fewer complications than thoracolumbar surgery (17.8%) [
5]. Complications are the most frequent reason for hospital readmissions [
3], with the AHRQ reporting readmission rates of 6.4% for fusions, and 6.5% for laminectomy [
2].
Surgical complications have varying levels of severity, with some causing only minor symptoms and others leading to severe disability or even death [
6]. Although there are several complication indexes that exist, there are no specific tools that are advocated by clinical practice guidelines. One existing tool is the Clavien
–Dindo (CD) classification system [
7] (Table
1). The CD classification system separates surgical complications into five grades based on the treatment required to correct the complication.
Table 1
Clavien–Dindo classification description and frequency of surgical complications as reported by spine surgeons
Grade I–II Clavien–Dindo |
Does not require alterations in the postoperative course of treatment, or are without need for additional pharmacological, surgical, endoscopic, or radiological interventions to treat the complication itself | Adjacent level disease/disc herniation—minor [ 22] | 0 |
Requires pharmacological treatment with drugs, including blood transfusions and total parenteral nutrition | | 71 |
DVT/vascular/embolism [ 24] | 8 |
Fracture—minor medical [ 25] | 0 |
Fracture—minor surgical [ 25] | 0 |
| 26 |
GI/GU—minor surgical [ 26] | 0 |
Medical infection—minor [ 27] | 13 |
Wound infection—minor [ 28] | 13 |
Grade III–IV Clavien–Dindo |
Requires surgical, endoscopic, or radiological interventions to be corrected (III) or life-threatening single/multi-organ dysfunctions that require ICU management (IV) | Adjacent level disease/disc herniation—major [ 29] | 0 |
Bleeding/transfusion [ 30] | 55 |
| 261 |
Fracture—major medical [ 25] | 0 |
Fracture—major surgical [ 25] | 0 |
| 2 |
GI/GU—major surgical [ 26] | 3 |
| 41 |
Medical infection—major [ 33] | 1 |
| 19 |
| 1 |
Wound infection—major [ 28] | 0 |
Grade V Clavien–Dindo |
Results in death of the patient | Death | 2 |
To our knowledge, two studies have explored the role of complication severity on outcomes [
8,
9]. Glassman et al. [
8] explored the influence of major and minor perioperative complications of spine surgery on 1-year disability, pain, and quality of life outcomes and found that major complications, although rare, negatively influenced quality of life. Fritzell et al. [
9] compared complications among three different types of fusion surgery and found no significant differences between complications ranked major or minor and 2-year outcomes [
9]. Both studies involved small sample sizes of individuals with complications (<100). Our goal was to explore the relationship between severity (by rank) of perioperative outcomes with disability and pain outcomes at both 1- and 2-year time frames in a larger sample of patients who experienced complications. We hypothesized that those with higher categorization according to the CD classification would exhibit poorer outcomes for disability and pain [
7].
Results
The complication grades were I/II (
N = 120) and III/IV (
N = 356) (Table
3). Follow-up ODI scores were collected in 62.1% of patients at 1 year, and 35.8% at 2 years. The follow-up rates for the VAS at 1 and 2 years were 58.9 and 35.8%, respectively. When comparing high and low complication categories, statistically significant differences were present for number of levels of surgery addressed (2.7 vs 1.6), higher levels of reported baseline disability, and lower baseline levels of reported quality of life (both MCS and PCS).
Table 3
Descriptive baseline comparisons of high (I–II) and low (III–IV) complication groups by Clavien–Dindo classification
Age | 58.3 (13.9) | 60.0 (12.9) | 0.26 |
Gender | 53 F 42 M 24 Not reported | 215 F 139 M 12 Not reported | 0.38 |
Body mass index | 28.8 (6.3) | 29.8 (6.2) | 0.21 |
Baseline pain score | 7.1 (2.5) | 7.2 (2.4) | 0.58 |
Baseline ODI score | 47.9 (16.4) | 51.4 (13.6) |
0.04
|
Baseline SF-36 PCS score | 30.7 (8.9) | 27.6 (6.4) |
<0.01
|
Baseline SF-36 MCS score | 41.7 (12.3) | 37.7 (14.1) |
<0.01
|
Levels of surgery | 1.6 (1.0) | 2.7 (1.3) |
<0.01
|
Number of patients with prior surgery | 29 Y 90 N | 73 Y 285 N | 0.36 |
1-year VAS percent change | 25 Y 23 N | 123 Y 110 N | 0.92 |
2-year VAS percent change | 18 Y 8 N | 75 Y 72 N |
0.03
|
1-year ODI percent change | 25 Y 26 N | 121 Y 124 N | 0.96 |
2-year ODI percent change | 21 Y 13 N | 78 Y 103 N |
0.04
|
Unadjusted univariate regression analyses suggest that lower levels of CD classification were significantly associated with increased improvement at final outcome (2 years) in both pain (OR 2.88; 95% CI 1.08, 7.66) and disability (OR 2.13; 95% CI 1.01, 4.52), a finding that was not significant at 1 year. In patients who experienced Grade I−II complications, there was significantly increased improvement in pain and outcome compared to patients who experienced Grade III–IV complications.
When gender, levels of surgery, baseline disability, and quality of life (MCS and PCS) were used as controls, the adjusted multivariate analyses suggest that CD classification does not contribute to pain and disability outcomes at 1 or 2 years. Table
4 provides the findings of univariate and multivariate regression analyses.
Table 4
Comparative analyses of disability and pain by Clavien−Dindo classification at 1 and 2 years (30% difference)
Unadjusted oswestry disability score |
Grade I–II Clavien–Dindo classification (year 1) | 0.98 (0.54, 1.80) | 0.96 |
Grade I–II Clavien–Dindo classification (year 2) | 2.13 (1.01, 4.52) |
0.04
|
Adjusted Oswestry Disability Scorea
| | |
Grade I–II Clavien–Dindo classification (year 1) | 1.13 (0.57, 2.21) | 0.72 |
Grade I–II Clavien–Dindo classification (year 2) | 1.74 (0.73, 4.19) | 0.21 |
Unadjusted visual analog scale for pain |
Grade I–II Clavien–Dindo classification (year 1) | 0.97 (0.52, 1.81) | 0.93 |
Grade I–II Clavien–Dindo classification (year 2) | 2.88 (1.08, 7.66) |
0.03
|
Adjusted visual analog scale for paina
|
Grade I–II Clavien–Dindo classification (year 1) | 0.91 (0.45, 1.82) | 0.78 |
Grade I–II Clavien–Dindo classification (year 2) | 2.23 (0.78, 6.36) | 0.13 |
Discussion
The aim of this study was to determine the relationship between the severity of perioperative complications and 1- and 2-year outcomes using the ODI and VAS. During the perioperative phase, the severity of complications can vary significantly, which necessitates the use of a classification system to rank complications based on severity when relating complications to outcomes. Furthermore, perioperative complications are usually medical or surgical-based and the long-term relationship between these variables and patient outcomes is unexplored. We used the CD classification system, which ranks severity into five ordinal categories based on the therapeutic intervention used to manage the complication [
7]. Our findings suggest no significant relationship between the severities of perioperative complications at 1 year; however, at 2 years those in the Grade III–IV category (higher severity) had significantly worse outcomes in both the ODI and VAS in an unadjusted model. However, when controlled for baseline characteristics, there were no significant relationships between the two groups at either 1 or 2 years with each of the outcome measures. There are a number of potential reasons for these findings.
The most common spine surgery complication requiring readmission is wound infection of the surgical site [
3]. Wound infections most commonly manifest around 13 days, long after the individual has been discharged from the hospital or ambulatory care center [
16]. We studied perioperative complications and the most commonly seen were cerebrospinal fluid leakage and dural tears, cardiac/pulmonary related, and bleeding/transfusions. We hypothesized that the severity of complications identified in the study would influence long-term morbidity (pain and disability). Contrary to our hypothesis, the baseline characteristics of the individual influenced outcomes more than the perioperative complication severity of the individuals when adjusted in the modeling.
As stated, other factors may influence outcomes more than complications. Baseline differences were present among those in the low and higher severity groups for a number of spinal levels of surgery, quality of life scores, and disability scores. Operating on more spinal levels increases risk for injury in a greater number of neighboring structures, and performing surgery at specific levels may lead to a greater risk for serious complication [
17]. Benedetti-Valentini et al. explained this in regard to performing disc surgery and laminectomy at L1-L2, where there is a risk for perforation of the abdominal aorta and inferior vena cava based on location. Psychological factors such as depression and poor SF-36 MCS scores (which measures emotional health, vitality, social and general health perceptions) are associated with poorer outcomes [
14]. Non-favorable outcomes have also been associated with catastrophizing and neuroticism at baseline [
14].
Although not formally investigated, we feel there is a chance that the baseline health status of the individuals in the higher CD classification reflected their poorer disability levels (captured with the ODI) and could have predisposed the individuals to greater complications. For example, within the literature diabetes is affiliated with an increased risk of infection during spinal surgery as is congestive heart failure, peripheral vascular disease, cerebrovascular disease, dementia, rheumatic disease, peptic ulcer, liver disease, hemiplegia, renal disease, malignancy, liver disease, metastasis, thrombophlebitis, fracture, alcoholism, scar, DVT, burns, dehydration and malnutrition [
18]. Certainly, requiring surgery to more levels complicates the process and increases the likelihood of bleeding, dural incision, etc. [
19,
20].
Another factor may be the outcome measures that were used in our study. In a 2003 study, Fritzell et al. [
9] examined the relationship between complications experienced during lumbar fusion surgery and outcome measures. They compared those with complications to those without, and found no significant association between complications and 2-year outcomes using the ODI and VAS. However, their study also included a Global Assessment of Treatment question at 2 years post operation where patients were asked if they were currently ‘much better’, ‘better’, ‘unchanged’, or ‘worse’ than before surgery. It should be noted that the Global Assessment of Treatment scale used in their study has not been validated, and the results should therefore be considered with some degree of apprehension. Although the finding lacked statistical significance (
P = 0.052) there was a trend toward patients who experienced complications to be less likely to reply ‘much better’ than those who were free of complications [
10]. This suggests that different outcome tools may lead to differences in results. It has been recommended that at least five different outcomes measures should be used for lumbar spine assessment of recovery, assessing the following five domains—back-specific function, health status, pain, work disability, and patient satisfaction [
21].
Our findings are very similar to a study by Glassman et al. [
8] who reported minimal differences in outcomes at 1 year when comparing those with no complications, minor complications and major complications [
9]. In this study by Glassman and colleagues, complications were classified as major or minor by a consensus agreement between the participating surgeons. The outcome measures considered were the SF-12 PCS, the SF-12 MCS, SF-12 domain-specific subscale, the ODI, the numeric rating score for back and neck pain, and the SRS-22 total score and subscale scores. There were no significant differences found between the complication groups in any of the utilized outcome measure scores except for the SF-12 general health subscale, where the score of the major complication group was significantly worse than the minor complication group. The score of the group with no complications was not significantly different than either of the other two groups.
Limitations
Although the present study utilized a sample size larger than any known previous studies on this subject, it not sufficiently comprehensive to conclusively delineate the long-term risk associated with the severity of perioperative complications experienced by all patients undergoing lumbar spine surgery. A larger sample size that encompasses a more diverse patient population in terms of baseline characteristics and primary conditions would improve the study’s external validity. Furthermore, the follow-up rates of this study were of a smaller percentage than those typically seen in prospective designs or trials. Another limitation of the present study was the varying number of techniques used for surgical correction. The database included inputs for anterior lumbar interbody fusion, posterior lumbar interbody fusion, extreme lumbar interbody fusion, transforaminal lumbar interbody fusion, posterolateral fusion, posterior posterolateral fusion, and options for open access or minimally invasive techniques. While it was important to capture as many surgical outcomes as possible, we did not control for the risks associated with different types of surgical techniques.