Introduction
The reported incidences of incidental durotomies (0.5%–18%) or “dural tears” are highly variable, likely due to differences in surgical complexity and patient-specific risk factors [
1–
5]. Not mentioning the durotomy in the operative notes or failure to include an International Classification of Diseases (ICD) code for durotomy repair may also contribute to the wide range of reported durotomy incidences [
6–
8]. Definitive management of durotomies often includes primary surgical repair with nonabsorbable suture [
9]. Recently, new technologies have become available, including fat or muscle xenografts, collagen patches, fibrin glue, or other synthetic sealants [
10–
12].
Several studies showed that hospital stays are 150%–200% longer and readmission rates are almost doubled after lumbar spine surgeries complicated by dural tears [
5,
6,
12,
13]. A retrospective study reported no changes in complications, readmissions, or revision rates due to incidental durotomies [
14]. However, investigations into the effects of dural tears on patient-reported outcomes are limited. One study of patient outcomes demonstrated that intraoperative incidental durotomies resulted in more residual leg pain, inferior mental health quality of life, and greater disability compared with no durotomies [
5]. However, other studies have reported minimal to no differences in pain, quality of life, or disability 1 year after surgery [
8,
15,
16].
Understanding the risk factors and postoperative outcomes after incidental durotomies in patients undergoing lumbar decompression with or without fusion is important. Thus, the purpose of this study was to determine the incidence and risk factors for incidental durotomies during lumbar decompressions with or without fusion and the proportion of incidental durotomies documented by the International Classification of Disease, 10th revision (ICD-10) codes. Changes in patient-reported outcome measures (PROMs) due to durotomies and the repair methods were also determined.
Materials and Methods
1. Data collection and study design
This study was exempt from informed consent from the institutional review board (IRB) due to its retrospective nature and low risk to subjects. After IRB approval (Thomas Jefferson University, Control #19D.508), a retrospective review of electronic medical records was conducted for patients who underwent lumbar decompression from April 2017 to May 2021 using the current procedural terminology codes (63005, 63012, 63017, 63030, 63042, 63047, or 63056). Sixteen fellowship-trained orthopedic spine surgeons performed the surgeries. Patient demographics, surgical characteristics, surgical outcomes, and preoperative and 1-year postoperative PROMs were collected, including the Oswestry Disability Index (ODI), the Short-Form 12 Physical Component (PCS-12), the Mental Component (MCS-12), and Visual Analog Scale (VAS) back and leg pain scores (OBERD, Columbia, MO, USA).
Due to the suspected low rates of incidental durotomy reporting and the inaccuracies in ICD-10 classifications, intraoperative incidental durotomies were determined using our institution’s surgical equipment log. Intraoperative durotomies were defined as surgical cases using specialty equipment specifically for incidental durotomy repairs performed by orthopedic spine surgeons, as the neurosurgical department also performs intradural procedures. The specialty equipment included specialized sutures, dural sealant, and collagen-based grafts. While other repair methods exist, including fibrin glue and muscle or fat xenografts, our surgeons did not utilize these methods. Moreover, all orthopedic spine surgeons at our institution repair incidental durotomies with these techniques regardless of the tear severity. Diagnosis of intraoperative incidental durotomy was also determined using the ICD-10 codes, including G96.11 and G97.41.
2. Statistical analysis
Patients were grouped based on the presence or absence of an intraoperative incidental durotomy. A delta value (Δ) was calculated for each PROM by subtracting the preoperative value from the 1-year postoperative value. Continuous data were reported as means and standard deviations. Categorical data were compared with chi-square tests. Intragroup comparisons were performed using paired t-tests. The presence of an incidental durotomy and other patient demographics (age, sex, body mass index [BMI], and Charlson comorbidity index [CCI]) were categorized as independent variables in the logistic regression analysis for hospital readmissions, the Poisson regression analysis for the length of hospital stay, and the linear regression for ΔPROMs.
To identify independent surgical risk factors for incidental durotomies while accounting for differences in patient demographics, a 3:1 propensity-matched analysis was conducted controlling for age, sex, BMI, smoking status, and CCI. Patients without intraoperative incidental durotomies were matched in a 3:1 fashion to patients who underwent intraoperative incidental durotomies. Stepwise logistic regression analysis was performed to identify significant surgical variables associated with intraoperative incidental durotomies. For ICD-10 codes, sensitivity and specificity were reported compared to the specialty equipment log. A p<0.05 was considered statistically significant. All statistical analyses were performed using RStudio ver. 4.0.2 (RStudio, Boston, MA, USA).
Discussion
Our retrospective cohort of 3,684 lumbar decompressions with and without fusions demonstrated an incidental durotomy rate of 14.5%. Risk factors for incidental durotomies included revision procedures, the number of surgical levels decompressed, and a preoperative diagnosis of spondylolisthesis or kyphosis. Intraoperative incidental durotomies were not independent predictors of increased hospital readmissions or worse ΔPROM improvement but did predict longer hospital stays. Dural repair with a combination of collagen graft and sutures was a significant independent predictor of decreased improvement in the 1-year postoperative VAS back compared to other dural repair methods, which may reflect worse outcomes in patients with more severe tears.
The rate of incidental durotomies in our study was similar to a prospective study of 76 patients undergoing lumbar spinal surgery at an academic center (15.8%) and a multicenter database study of 564 patients undergoing adult spinal deformity surgery (12.1%) [
17,
18]. Significant variability in durotomy incidence may be due to the procedure type, as discectomies and single-level procedures are lower risks than laminectomies and multi-level procedures [
4]. Additionally, lower incidental durotomy rates are reported in database studies, including PearlDiver, which reported a 2.8% incidence of durotomies [
6]. The lower rates may be due to a reliance on ICD codes, which have a sensitivity of only 5.4% in our analysis. A multicenter retrospective cohort study of 2,146 patients undergoing lumbar laminectomy reported an incidental durotomy rate of 7.7%, which was determined via a postoperative surgeon questionnaire [
8]. A 2015 systematic review reported an incidental durotomy rate of 9.57% in prospective studies, but only 4.52% in retrospective studies [
19]. These reports increase the validity of our incidence rate and support the finding that utilizing ICD codes may be underestimate durotomy rates.
The Spine Patient Outcomes Research Trial (SPORT), a multicenter prospective randomized controlled trial, reported an incidental durotomy rate of 9.0% in primary procedures for spinal stenosis [
7]. Our study was conducted at a tertiary academic center, which may explain the higher incidental durotomy incidence, given the relatively high rate of complex spondylolisthesis and deformity cases and the involvement of trainees [
8]. We also identified an increased incidence among patients with thoracolumbar kyphosis consistent with an analysis by Iyer et al. [
18], who reported that patients with reduced lumbar lordosis are at greater risk of incidental durotomy. Patients undergoing spinal fusions for deformities are more likely to require osteotomies, which may independently increase the risk of incidental durotomies [
18]. These deformities present on a continuum, and more severe diseases may require more aggressive correction yielding greater durotomy rates. Thus, future research evaluating the severity of spinal pathology on the risk of incidental durotomy is indicated.
Revision surgery is an important risk factor for incidental durotomy [
4,
8,
16,
18,
20,
21]. Prior lumbar surgery causes fibrosis and scar tissue formation, which adheres to the dura and complicates the separation of the two layers [
22]. Our study supports this finding; revision surgery was an independent predictor associated with a 73% increased risk of incidental durotomy. In addition, each level decompressed incurred an 11% increased risk of incidental durotomy, and spondylolisthesis or thoracolumbar kyphosis increased the risk of durotomy by 31% and 87%, respectively. These risk factors were previously identified [
4,
8,
18,
23].
Increasing age was associated with incidental durotomies with a mean difference of approximately 4 years according to the univariate analysis. Increasing age is a known risk factor for incidental durotomies due to the normal aging process, including spinal canal narrowing, ligamentum flavum hypertrophy, osteophyte formation, and shortening of the spine leading to redundant dura [
4,
18,
20,
21,
24]. While thickened dura protects against tearing, the fibrous degenerative changes during the aging process lead to friability and less elasticity, rendering the dura more prone to injury. Dural redundancy increases trapping of the Kerrison rongeur. BMI also correlates with incidental durotomy rates [
4]. However, this is not a universal finding. A recent meta-analysis of eight studies including 11,416 patients found no association between incidental durotomy and BMI, in agreement with our findings [
21].
Possible explanations for the disparate durotomy rates between our study and previous database studies include increased sample sizes in database studies and limitations inherent to database analysis, which are reliant on accurate ICD coding. ICD codes grossly underrepresented the true incidence of incidental durotomies with a sensitivity of only 5.4%. The inaccuracy of ICD codes may be due to medicolegal implications. The underestimation severely limits the validity of database studies focused on the rates and predictors of incidental durotomies [
25]. The limitations of ICD codes and database studies have been demonstrated by previous orthopedic studies [
26–
28].
The effects of incidental durotomies on postoperative PROMs have been the focus of many studies. A subset of 409 patients from the SPORT who underwent lumbar decompression, a separate retrospective cohort analysis of 2,907 lumbar surgery patients, and a retrospective cohort of 564 patients undergoing adult deformity surgery all found no significant differences in postoperative outcomes due to incidental durotomies [
7,
16]. A systematic review and meta-analysis of 11 studies, including over 65,000 patients, found only marginally diminished improvements in ODI and VAS leg in patients with intraoperative incidental durotomies but did not control for patient demographics with possible confounding outcomes between patient cohorts [
15]. Our study largely supports these studies, incidental durotomies were not independent predictors of ΔPROMs in the multivariate analysis.
Different techniques for incidental durotomy repair are effective, although a meta-analysis of 49 studies demonstrated suture repair has a lower rate of failure than indirect repair [
1]. In our study, incidental durotomy repair technique did not alter the length of stay or rate of hospital readmission in the multivariate analysis. Interestingly, patients with intraoperative incidental durotomy that were repaired with both collagen-based grafts and non-absorbable sutures had significantly worse improvements in VAS back in the multivariate analysis. To the authors’ knowledge, this relationship was not previously demonstrated. This finding may be related to the severity of the incidental durotomy, as patients with larger dural tears may require more intricate dural repairs. The dural repair equipment is subject to provider preference; thus, strong conclusions cannot be made regarding the role of the technique, which may be confounded by dural tear severity. Future research into the severity of intraoperative incidental durotomies is warranted to determine if a threshold exists at which intraoperative incidental durotomy may lead to diminished postoperative improvement.
Limitations of our study include those inherent to retrospective research. However, multivariate regression analyses and matching limited the confounding variables. We included numerous preoperative diagnoses but the severity and complications of diagnoses, such as the presence of a facet cyst, were not collected. Due to limitations in the availability of magnetic resonance imaging and preoperative radiographs permanently saved in our PACS, we were unable to determine if the degree of stenosis, kyphosis, or spondylolisthesis was associated with incidental durotomies. Another limitation is the rate of incomplete PROMs. We only included patients with a complete set of preoperative and 1-year postoperative PROMs, which allowed for a complete, balanced analysis. While bias may exist in this study due to the high percentage of incomplete PROMs, the rate of incidental durotomies and other patient demographics did not differ between these populations, limiting this potential bias. Equipment logs were utilized to determine the incidence of intraoperative incidental durotomies, which may be subject to inaccuracies if the product was incorrectly pulled. However, this method is superior to ICD codes utilized in large incidental durotomy database studies. Additionally, minor tears may not have been identified by the surgeon and did not require incidental durotomy repair kits. However, using ICD codes would also fail to capture the incidence of these tears. Furthermore, our study evaluated PROMs postoperatively for 1 year, but we were unable to determine if incidental durotomies influenced long-term outcomes and only a minority of patients were represented due to limitations in collecting both preoperative and 1-year postoperative PROMs.