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J Orthop Surg Res
J Orthop Surg Res
Journal of Orthopaedic Surgery and Research
1749-799X
BioMed Central London

5009
10.1186/s13018-024-05009-y
Research Article
The effect of high-normal preoperative international normalized ratios on postoperative outcomes and complications following posterior cervical spine surgery
Strony John T. johntstrony@gmail.com

1
Sabbagh Ramsey S. 1
Ahn Junyoung 2
Du Jerry Y. 1
Ahn Uri M. 3
Ahn Nicholas U. 4
1 grid.443867.a 0000 0000 9149 4843 Department of Orthopaedics, University Hospitals/Cleveland Medical Center, 11100 Euclid Avenue, Cleveland, OH 44106 USA
2 https://ror.org/01j7c0b24 grid.240684.c 0000 0001 0705 3621 Department of Orthopaedic Surgery, Rush University Medical Center, 1611 W Harrison St., Chicago, IL 60612 USA
3 https://ror.org/04x545z07 grid.512387.a New Hampshire NeuroSpine Institute, 4 Hawthorne Dr., Bedford, NH 03110 USA
4 https://ror.org/01ckdn478 grid.266623.5 0000 0001 2113 1622 Department of Orthopaedic Surgery, University of Louisville, 215 Central Avenue, Suite 201, Louisville, KY 40208 USA
9 9 2024
9 9 2024
2024
19 5522 6 2024
19 8 2024
© The Author(s) 2024
2024
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Introduction

Current guidelines recommend that the International Normalized Ratio (INR) be less than 1.5 prior to spine intervention. Recent studies have shown that an INR > 1.25 is associated worse outcomes following anterior cervical surgery. We sought to determine the risk of complications associated with an INR > 1.25 following elective posterior cervical surgery.

Methods

The American College of Surgeons National Surgical Quality Improvement Program database was queried. Patients undergoing elective posterior cervical surgery from 2012 to 2016 with an INR level within 24 h of surgery were included. Primary outcomes were hematoma requiring surgery, 30-day mortality, and transfusions within 72-hours. There were 815 patients in the INR ≤ 1 cohort (Cohort A), 410 patients in the 1 < INR ≤ 1.25 cohort (Cohort B), and 33 patients in the 1.25 < INR ≤ 1.5 cohort (Cohort C).

Results

Cohort C had a higher rate of transfusion (4% Cohort A; 6% Cohort B; 12% Cohort C; p = 0.028) and the rate of mortality within 30 days postoperatively trended toward significance (0.4% Cohort A; 0.5% Cohort B; 3% Cohort C; p = 0.094). There was no significant difference in the rate of postoperative hematoma formation requiring surgery (0.2% Cohort A; 0% Cohort B; 0% Cohort C; p = 0.58). On multivariate analysis, increasing INR was not associated with an increased risk of developing a major complication.

Conclusion

An INR > 1.25 but ≤ 1.5 may be safe for posterior cervical surgery. An INR > 1.25 but ≤ 1.5 was associated with a significantly higher rate of transfusions. However, increasing INR was not significantly associated with increased risk of any of the major complications.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13018-024-05009-y.

issue-copyright-statement© BioMed Central Ltd., part of Springer Nature 2024
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pmcIntroduction

Surgical management of degenerative cervical myelopathy and cervical radiculopathy is widely prevalent and largely effective at improving functionality and alleviating debilitating symptoms [1–5]. The cervical spine can be approached anteriorly, posteriorly, or via combined approaches. The approach that is chosen is dependent upon patient characteristics, radiographic findings, and surgeon familiarity and preference. Significant complications can occur following cervical spine surgery regardless of the approach, including the formation of epidural hematomas. Epidural hematomas occur with relative frequency [6, 7] yet are commonly asymptomatic [8]. On rare occasions, an epidural hematoma can expand to a critical mass such that the neighboring neural elements become compressed, resulting in neurologic compromise. Despite operative intervention, the sequelae of this complication may result in patients having no significant improvement in quality-of-life outcomes when compared to their preoperative state [8]. It is therefore imperative to identify potentially at-risk patients and optimize risk-factors to avoid this devastating complication.

The safe management of perioperative coagulopathy is of paramount importance, particularly in patients scheduled to undergo elective spine surgery who are also receiving anticoagulation therapy for conditions like atrial fibrillation, myocardial infarction, thromboembolic disease, and mechanical heart valves [9, 10]. The international normalized ratio (INR) is a laboratory parameter that was introduced as a standardized reporting mechanism that allows clinicians to accurately compare the prothrombin time across patients and different laboratories [11, 12]. Current guidelines recommend that the INR should be < 1.5 prior to elective spine interventions to minimize the risk of bleeding [13, 14]. However, recent analyses of the American College of Surgeons (ACS) National Surgical Quality Improvement Program (NSQIP) database have called the current guidelines into question. An INR of 1.25 to 1.5 was associated with significantly increased rates of postoperative bleeding events and mortality following total knee arthroplasty (TKA) [15], increased bleeding events following total hip arthroplasty (THA) [16], and increased rates of symptomatic hematoma formation, readmission, and reoperation following elective anterior cervical spine surgery [17]. Additionally, posterior cervical surgery may be associated with higher rates of symptomatic epidural hematomas when compared to anterior cervical surgery [8, 18]. Posterior cervical procedures are associated with larger amounts of intraoperative blood loss and larger exposures which confer added risk to the disruption of the paraspinal musculature and epidural venous plexus during lateral or foraminal decompression [18, 19]. In light of these recent findings, the purpose of this study was to determine the risk of complications associated with an elevated preoperative INR, specifically an INR > 1.25, following elective posterior cervical spine surgery.

Materials and methods

Data source

The ACS NSQIP database was utilized for this study [20, 21]. The NSQIP database is a prospectively collected surgical outcomes database. Data on demographics, comorbidities, perioperative details, and 30-day postoperative complications for major surgical cases are provided by participating hospitals. The program collects data prospectively and audits participating sites for accuracy and reproducibility [20, 22, 23].

Required NSQIP statement: “American College of Surgeons National Surgical Quality Improvement Program and the hospitals participating in the ACS NSQIP are the source of the data used herein; they have not verified and are not responsible for the statistical validity of the data analysis or the conclusions derived by the authors.”

Case selection

Cases in the NSQIP database from 2012 to 2016 were included for analysis because International Classification of Diseases 9th and 10th Revisions (ICD-9 and ICD-10, respectively) codes began to be assigned to readmissions and reoperations in 2012. Neurosurgeon and orthopedic surgeon spine cases with spine-related Current Procedural Terminology (CPT) codes (Table S1) were identified (n = 206,395). Emergency (n = 4,546), non-elective cases (n = 14,084), and patients with no preoperative INR (n = 74,225) were excluded. Patients with INR within 1 day of surgery were included (n = 15,357). A total of 1,599 patients with posterior cervical spine surgery procedures were identified. Patient with concurrent anterior surgery or thoracic, lumbar, or sacral surgery were excluded, leaving 1,269 patients. These cases were further stratified by their preoperative INR. Patients with a preoperative INR > 1.5 were excluded due to the previously described risks associated with an INR > 1.5. Thus, three INR cohorts were constructed: INR ≤ 1, 1 < INR ≤ 1.25, and 1.25 < INR ≤ 1.5. For simplicity, the INR ≤ 1 cohort is referred to as Cohort A, the 1 < INR ≤ 1.25 cohort is referred to as Cohort B, and the 1.25 < INR ≤ 1.5 cohort is referred to as Cohort C. A total of 1,258 patients were included in the final analysis.

Outcomes of interest

The primary outcomes of interest were postoperative hematoma requiring surgery, 30-day mortality, and transfusions within 72 h of surgery. Reoperation events specifically associated with ICD-9 or ICD-10 diagnosis of postoperative hematoma (ICD-9: 998.1, 998.12, 998.13, ICD-10: G97.51, G97.52) were used to identify this complication. Mortality and transfusion events are specifically tracked by the NSQIP. Secondary outcomes of interest were unplanned 30-day readmissions, reoperation within 30 days of index surgery, wound dehiscence, surgical site infection, sepsis, septic shock, deep vein thrombosis (DVT), pulmonary embolism, myocardial infarct, cardiac arrest, pneumonia, progressive and acute renal failure, urinary tract infection, stroke, and hospital length of stay (LOS).

Confounding variables

Demographics, comorbidities, laboratory, perioperative, and procedural data were compared between cohorts to identify potential confounders. Demographic factors assessed included age, sex, and ethnicity. Comorbidities assessed included body mass index (BMI), American Society of Anesthesiologists (ASA) class, diabetes (insulin and non-insulin dependent), hypertension requiring medication, smoking status, cardiac disease (history of congestive heart failure or dyspnea), respiratory disease (history of ventilator-assisted respirations 48 h prior to surgery or chronic obstructive pulmonary disease), renal disease (history of renal failure or previous dialysis), corticosteroid use for chronic conditions, bleeding disorders, and disseminated cancer. Aberrant laboratory values were defined as follows: hyponatremia as serum sodium < 135mEq/L, hypernatremia as serum sodium > 145mEq/L, leukocytosis as WBC > 12000/mm3, leukopenia as WBC < 4000/mm3, anemia as hematocrit < 40.6%, and thrombocytopenia as platelets < 150,000/µL) as consistent with prior literature.15–18 Perioperative details assessed included operative time, wound class, and surgeon specialty. Procedural details included type of surgery, region of surgery, approach, number of levels, revision surgery, dural repair, and use of microscope as identified by CPT codes (Supplemental Table 1).

Statistical analysis

Categorical variables are denoted as percentages and continuous variables are expressed as mean ± standard deviation. Univariate analysis comparing confounding variables and differences in complications among INR cohorts was performed using Kruskal-Wallis test, Chi-squared and Fisher’s exact tests as appropriate. Multivariate models were created to assess the association of INR with complications that were significantly different on univariate analysis (p < 0.05), adjusting for confounding variables significant on univariate analysis (p < 0.05). Binary logistic regressions were utilized for categorical complications and linear regression models were utilized for continuous complications. Statistical analysis was performed using SPSS (SPSS 25.0, IBM, Armonk, NY).

Ethics committee statement

This was a study of a publicly accessible database. After discussion with the institutional review board (IRB), neither approval from the IRB nor consent from patients was required to conduct this study.

Results

Patients and univariate analysis of potential confounding variables

A total of 1,258 patients were included in the final analysis. There were 815 patients in Cohort A (INR ≤ 1 cohort), 410 patients in Cohort B (1 < INR ≤ 1.25 cohort), and 33 patients in Cohort C (1.25 < INR ≤ 1.5 cohort). The mean INR value was 1 ± 0 for Cohort A, 1.1 ± 0.1 for Cohort B, and 1.3 ± 0.1 for Cohort C.

A comparison of demographics and medical comorbidities among the three INR cohorts can be found in Table 1. There were statistically significant differences in the mean age (58.5 ± 13.4 Cohort A; 62 ± 13.6 Cohort B; 66.8 ± 14.5 Cohort C; p < 0.001), sex (61% male Cohort A; 71% male Cohort B; 73% Cohort C; p = 0.001), percentage of patients with an American Society of Anesthesiologists (ASA) score ≥ 3 (57% Cohort A; 70% Cohort B; 82% Cohort C; p < 0.001), and medical comorbidities including hypertension (53% Cohort A; 60% Cohort B; 70% Cohort C; p = 0.018), presence of a bleeding disorder (3% Cohort A; 5% Cohort B; 21% Cohort C; p < 0.001), and disseminated cancer (1% Cohort A; 3% Cohort B; Cohort C; p = 0.018).

Table 1 Comparison of demographics and comorbidities by INR cohort

Demographics and comorbidities	INR Cohort	
INR ≤ 1 (n = 815)	1 < INR ≤ 1.25 (n = 410)	1.25 < INR ≤ 1.5 (n = 33)	P-value	
Age, n (%)	Years ± SD	58.5 ± 13.4	62.0 ± 13.6	66.8 ± 14.5	< 0.001	
Sex, n (%)	Male	495 (61%)	291 (71%)	24 (73%)	0.001	
Female	320 (39%)	119 (29%)	9 (27%)	
Ethnicity, n (%)	Caucasian	613 (75%)	303 (74%)	23 (70%)	0.227	
African American	94 (12%)	63 (15%)	5 (15%)	
Asian/ Pacific Islander	27 (3%)	6 (2%)	0 (0%)	
Native American/ Pacific Islander	13 (2%)	7 (2%)	0 (0%)	
Body Mass Index, n (%)	Mean ± SD	29.3 ± 6.7	29.7 ± 6.9	31.6 ± 8.7	0.304	
American Society of Anesthesiologists Class, n (%)	1–2	350 (43%)	124 (30%)	6 (18%)	< 0.001	
3–5	459 (57%)	286 (70%)	27 (82%)	
Specific Comorbidities, n (%)	Diabetes	174 (21%)	78 (19%)	10 (30%)	0.254	
Hypertension	432 (53%)	246 (60%)	23 (70%)	0.018	
Smoking	225 (28%)	91 (22%)	7 (21%)	0.103	
Cardiac Disease	8 (1%)	3 (1%)	1 (3%)	0.422	
Respiratory Disease	40 (5%)	31 (8%)	3 (9%)	0.129	
Renal Disease	8 (1%)	7 (2%)	0 (0%)	0.443	
Corticosteroid	57 (7%)	21 (5%)	1 (3%)	0.328	
Bleeding Disorder	28 (3%)	22 (5%)	7 (21%)	< 0.001	
Disseminated Cancer	11 (1%)	14 (3%)	2 (6%)	0.018	
Bold values: p < 0.05

Supplemental Table 2 compares common preoperative laboratory values across the three cohorts. There were significant differences in the frequency of eunatremia (92% Cohort A; 89% Cohort B; 74% Cohort C; p = 0.018), normal white blood cell counts (91% Cohort A; 92% Cohort B; 73% Cohort C; p = 0.002), anemia (46% Cohort A; 55% Cohort B; 79% Cohort C; p < 0.001) and thrombocytopenia (6% Cohort A; 11% Cohort B; 27% Cohort C; p < 0.001).

A comparison of operative details is tabulated in Supplemental Table 3. There were significant differences in the frequency of wound class 1–2 (99% Cohort A; 99% Cohort B; 94% Cohort C; p = 0.032), procedures performed by orthopaedic surgeons (14% Cohort A; 14% Cohort B; 30% Cohort C; p = 0.037), and decompression (87% Cohort A; 79% Cohort B; 70% Cohort C; p = 0.003) among the three cohorts.

Univariate analysis of complications

Table 2 compares the rates of postoperative complications, including major (i.e., primary outcomes of interest) and minor complications, among the three cohorts. Regarding major complications, there was not a significant difference among the three cohorts with respect to the rate of postoperative hematoma formation requiring surgery (0.2% Cohort A; 0% Cohort B; 0% Cohort C; p = 0.58). The rate of mortality within 30 days postoperatively trended toward significance, with Cohort C experiencing a higher rate (0.4% Cohort A; 0.5% Cohort B; 3% Cohort C; p = 0.094). Additionally, Cohort C had a significantly higher rate of transfusion (4% Cohort A; 6% Cohort B; 12% Cohort C; p = 0.028) on univariate analysis.

Table 2 Comparison of complications by INR cohort

Complication	INR cohort	P-value	
INR ≤ 1 (n = 815)	1 < INR ≤ 1.25 (n = 410)	1.25 < INR ≤ 1.5 (n = 33)		
Major Complications	
Postoperative Hematoma Requiring Surgery	2 (0.2%)	0 (0%)	0 (0%)	0.580	
Mortality*	3 (0.4%)	2 (0.5%)	1 (3%)	0.094	
Transfusion	32 (4%)	26 (6%)	4 (12%)	0.028	
Minor Complications	
Readmissions*	43 (5%)	39 (10%)	3 (9%)	0.018	
Reoperations*	32 (4%)	16 (4%)	5 (15%)	0.007	
Wound dehiscence	6 (1%)	3 (1%)	0 (0%)	0.885	
Surgical Site Infection	21 (3%)	13 (3%)	1 (3%)	0.834	
Deep vein thrombosis	8 (1%)	5 (1%)	3 (9%)	0.003	
Pulmonary embolism	5 (1%)	3 (1%)	0 (0%)	0.871	
Stroke	1 (0.1%)	0 (0%)	0 (0%)	0.762	
Hospital length of stay (days)	4.4 ± 5.3	5.1 ± 6.5	9.2 ± 9.3	< 0.001	
*within 30 days postoperatively

Regarding the development of minor complications, Cohort C had significantly longer mean hospital LOS (4.4 ± 5.3 Cohort A; 5.1 ± 6.5 Cohort B; 9.2 ± 9.3 Cohort C; p < 0.001) as well as significantly higher rates of reoperations (4% Cohort A; 4% Cohort B; 15% Cohort C; p = 0.007) and DVT (1% Cohort A; 1% Cohort B; 9% Cohort C; p = 0.003) when not controlling for confounding variables. Cohort B had a significantly higher rate of readmissions (5% Cohort A; 10% Cohort B; 9% Cohort C; p = 0.018). There were no other significant differences on univariate analysis.

Multivariate analysis of major complications

Table 3 demonstrates the adjusted risk of developing a major complication (i.e., hematoma formation requiring surgery, mortality, and transfusion), when controlling for the previously identified confounding variables. When using Cohort A as the reference, the adjusted odds ratio (aOR) of mortality in Cohort B and Cohort C was 0.183 (95% CI 0.01–3.486, p = 0.258) and 0.149 (95% CI 0.007–3.020, p = 0.215), respectively. Likewise, the aOR of transfusion in Cohort B was 0.695 (95% CI 0.188–2.579, p = 0.587) and for Cohort C was 0.86 (95% CI 0.233–3.182, p = 0.821).

Table 3 Adjusted risk of bleeding, surgical site infection, and mortality by INR cohort

Variable	Post-operative Hematoma	Mortality*	Transfusion	
aOR (95% CI)	P value	aOR (95% CI)	P value	aOR (95% CI)	P value	
INR Cohort	INR ≤ 1	Ref	Ref	Ref	Ref	Ref	Ref	
1 < INR ≤ 1.25	-	-	0.183 (0.010-3.486)	0.258	0.695 (0.188–2.579)	0.587	
1.25 < INR ≤ 1.5	-	-	0.149 (0.007–3.020)	0.215	0.860 (0.233–3.182)	0.821	
*within 30 days

Discussion

The results of this current analysis of the American College of Surgeons (ACS) National Surgical Quality Improvement Program (NSQIP) database establish that an INR > 1.25 but ≤ 1.5 on the day prior to elective posterior cervical spine surgery was associated with a significantly higher rate of transfusions on univariate analysis. There was not a significantly increased rate of developing a postoperative hematoma requiring surgery but there was a trend towards significance regarding 30-day mortality rate. Elevated preoperative INR was also associated with significantly higher rates of readmission, reoperations, and longer hospital LOS on univariate analysis. However, when controlling for potentially confounding variables, there were no significant differences in the risk of developing a major complication between the three INR cohorts.

Symptomatic epidural hematomas following cervical spine surgery are rare but can confer significant morbidity and mortality. Schroeder et al. [8]. performed a large, multicenter retrospective case series in order to determine the incidence and circumstances surrounding the development of a symptomatic postoperative epidural hematoma in the cervical spine. A total of 16,582 cervical spine surgeries were identified of which 15 patients developed a postoperative epidural hematoma for an incidence of 0.09%. Furthermore, 6 (40%) of these 15 patients had residual neurologic deficits and there was no significant improvement in health-related quality-of-life metrics at final follow-up compared to their preoperative state. Although this series did not comment on potential risk factors, other studies have demonstrated that the presence of preoperative coagulopathy was a significant risk factors for the development of a symptomatic epidural hematoma following spine surgery [24, 25].

Current guidelines recommend that the INR should be < 1.5 prior to elective spine interventions to minimize the risk of bleeding [13, 14]. However, recent studies may support the notion that the INR should be less than 1.25 prior to orthopaedic surgery. Rudasill et al. [15]. retrospectively reviewed the ACS NSQIP database for adult patients who underwent primary TKA from 2010 to 2016 and 21,239 patients were included. In their results, an INR > 1.25 to 1.5 was associated with a significantly increased risk of bleeding requiring transfusion (aOR 1.29, 95% CI 1.02–1.63, p = 0.033) and mortality (aOR 3.37, 95% CI 1.31–8.63, p = 0.011) when compared to their INR ≤ 1 cohort. Likewise, an INR > 1.5 was also associated with a significantly increased risk of bleeding requiring transfusion (aOR 2.02, 95% CI 1.29–3.14, p = 0.002) and any infection (aOR 5.34, 95% CI 2.45–11.68, p < 0.001), including superficial, deep, and organ space infections. Rudasill et al. [16]. performed a similar analysis of the ACS NSQIP database for adult patients who underwent primary THA from 2005 to 2016 and 17,567 patients were included. Their primary outcome was bleeding requiring a transfusion within 72 h postoperatively. They showed that an INR > 1.25 to 1.5 was associated with a significantly increased risk of bleeding requiring a transfusion (aOR 1.55, 95% CI 1.26–1.92, p < 0.001) and any infection (aOR 1.71, 95% CI 1.04–2.82, p = 0.036) while an INR > 1.5 was associated with a significantly increased risk of bleeding (aOR 1.55, 95% CI 1.15–2.08, p = 0.004), mortality (aOR 2.69, 95% CI 1.07–6.76, p = 0.035), and readmissions (aOR 1.57, 95% CI 1.01–2.45, p = 0.045) when compared to the INR ≤ 1 cohort. Strony et al. [17]. reviewed 2,949 patients who underwent anterior cervical spine surgery. An INR > 1.25 but ≤ 1.5 was associated with a significantly increased risk of postoperative hematoma formation requiring surgery (aOR 11.92, 95% CI 1.79–79.33, p = 0.010) and reoperations (aOR 3.33, 95% CI 1.02–10.88, p = 0.046). They concluded that there is added risk when performing anterior cervical spine surgery in the setting of high-normal preoperative INR.

Despite the results of these previous studies, our results demonstrate that there is no significantly increased adjusted risk of postoperative hematoma formation requiring surgery, mortality, or transfusion within 72 h following posterior cervical spine surgery. These discrepancies between our results and the results of Strony et al. [17]. may lie within the inherent differences between the anterior and posterior approach to the cervical spine. The anterior approach to the cervical spine involves meticulous and careful dissection around numerous critical structures, including the trachea, esophagus, recurrent laryngeal nerve, and carotid artery [26]. As can occur following posterior cervical spine surgery, anterior cervical spine surgery can be complicated by the formation of an epidural hematoma that compresses the neural elements and results in neurologic dysfunction. However, there is an added and unique risk of airway compromise secondary to hematoma formation following anterior cervical approaches. Considering the results of the current study and the distinctions between anterior versus posterior cervical spine surgery, we believe that the previous guideline recommending an INR < 1.5 prior to spine intervention [13, 14] may still be applicable to posterior cervical spine procedures.

A paradoxical finding of our study was that patients in Cohort C (i.e., those with an INR of 1.25 < INR ≤ 1.5) had a significantly higher rate of DVT when compared to Cohorts A and B on univariate analysis. This observation may be explained by the significantly higher rate of patients in Cohort C who had an ASA score of 3, 4, or 5. In addition, the incidence of patients in Cohort C who carried a preoperative diagnosis of a “bleeding disorder” was significantly higher compared to Cohorts A and B. An inherent limitation to the NSQIP database is that the definition of “bleeding disorder” was not specifically defined. It is plausible that these patients were afflicted by hyper-coagulable disorders, thus predisposing these individuals to increased rates of VTE. The hospital LOS was found to be almost twice as long in Cohort C compared to Cohorts A and B. We believe that this finding can again be explained by the significantly higher ASA scores in Cohort C. Numerous studies within the orthopaedic literature have demonstrated that higher preoperative ASA scores were associated with worse outcomes and longer LOS [27–31].

Limitations

The results of this study must be interpreted within its limitations. First, patients within the NSQIP database are only followed for 30 days postoperatively. Longer-term outcomes and complications that occur after 30 days are not captured and therefore cannot be analyzed. Although there have been reports of delayed hematoma formation following spine surgery [32], hematoma requiring intervention is most relevant in the acute postoperative setting [33]. Second, the accuracy and quality of the data is entirely dependent upon the reporting practices of the participating hospitals. Analyses can be biased or incomplete if reporting and documentation is flawed. Third, as the limitations pertain to the NSQIP database, the data are from participating hospitals and may not reflect all hospitals or surgical procedures. A hospital’s choice to participate may be influenced by its interest in quality improvement, introducing bias and limiting generalizability. Fourth, it is unclear if any intervention was provided to patients with elevated INR levels prior to surgery. It may be unlikely that an intervention was provided because the current guidelines recommend an INR < 1.5 prior to spine surgery and patients with an INR > 1.5 were excluded from this analysis. Finally, although the presence of a “bleeding disorder” was quantified by the NSQIP database, the specific diagnoses which fall under this umbrella term were not elucidated. Therefore, we were not able to control for these preoperative diagnoses and coagulopathies in our multivariate analyses.

Conclusions

In contrast to recent studies investigating INR levels prior to anterior cervical spine surgery, an INR > 1.25 but ≤ 1.5 may be safe for posterior cervical spine surgery. An INR > 1.25 but ≤ 1.5 was associated with a significantly higher rate of transfusions on univariate analysis. However, increasing INR was not significantly associated with increased risk of any of the major complications on multivariate analysis.

Electronic supplementary material

Below is the link to the electronic supplementary material.

Supplementary Material 1

Supplementary Material 2

Supplementary Material 3

Author contributions

Study idea: UA, NA. Methodology: UA, NA, JA, JD, JS, RS. Data compilation and extraction: JA, JD, JS. Data analysis: RS, JD. Manuscript preparation: JS, RSReview of manuscript: UA, NA, JA, JD, JS, RS.

Funding

There were no external sources of funding for this study.

Data availability

American College of Surgeons National Surgical Quality Improvement Program and the hospitals participating in the ACS NSQIP are the source of the data used herein; they have not verified and are not responsible for the statistical validity of the data analysis or the conclusions derived by the authors.

Declarations

Institutional review board

This was a study of publicly accessible data. No IRB was needed for this study.

Competing interests

The authors declare no competing interests.

Publisher’s note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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