Risk factors for surgical site infection in elective routine degenerative lumbar surgeries

Abstract

Background Context

Surgical site infection (SSI) is one of the most serious complications of spine surgery. Its predisposing factors, especially in routine surgeries, are less reported. However, a number of patient- and procedure-related risk factors could be avoided or at least determined preoperatively. Moreover, the patient-specific risk for SSI could be estimated before the elective surgery.

Purpose

The aim of the present study was to analyze the preoperatively determinable risk factors for SSI in patients who require elective routine surgery related to lumbar disc degeneration and to build a multivariable model for the individual risk prediction.

Study Design

Analysis of prospectively collected standardized clinical data and the validation of the results on an independent prospective cohort were performed.

Patient Sample

One thousand thirty (N=1,030) patients were included in the study. All subjects underwent primary lumbar single- or two-level decompression, microdiscectomy, or instrumented fusion.

Outcome Measures

Occurrence of an SSI defined according to the current Centers for Disease Control and Prevention guidelines that required surgical or nonsurgical therapy.

Methods

The effect of preoperative patient characteristics, comorbidities, disease history, and invasiveness of the elective surgery on the risk of SSI was determined in uni- and multivariate logistic regression models in the test cohort (N=723). The performance of the final multivariable regression model was assessed by measuring its discriminative ability (c-index) in receiver operating characteristic analysis. Performance of the multivariable risk estimation model was tested on the validation (N=307) cohort.

Results

The prevalence of SSI was 3.5% and 3.9% in the test and in the validation cohorts, respectively. The final multivariable regression model predictive (p=.003) for SSI contained the patient's age, body mass index (BMI), and the presence of 5 comorbidities, such as diabetes, ischemic heart disease, arrhythmia, chronic liver disease, and autoimmune disease as risk factors. The c-index of the model was 0.71, showing good discriminative ability, and it was confirmed by the data of the independent validation cohort (c=0.72).

Conclusions

Predisposing factors for SSI were older age, higher BMI, and the presence of certain comorbidities in the present study. The cumulative number of risk factors significantly associated with the increasing risk for an SSI (p<.0001). Our model needs further validation but it may be used for individual risk assessment and reduction in the future.

Introduction

Surgical site infections (SSIs), defined as a hospital-acquired infection of the skin, soft tissue, or bone, are one of the most serious complications of spine surgery, increasing morbidity [1], mortality [2], unfavorable surgical outcomes [3], length of hospital stays, and costs [4], [5]. Spinal SSIs can be superficial (above the fascia) or deep (below the fascia). Spondylitis, discitis, spondylodiscitis, and epidural abscessare always defined as deep infections. Diagnosis of an SSI, which is based on signs and symptoms, laboratory and radiologic imaging findings, and microbiologic tests [6], and its management can be challenging for both clinician and patient.

Evidence & Methods

Surgical site infections are some of the most frequent and problematic complications following spine surgery. The authors attempt to devise a scoring system that may be able to inform the risk of surgical site infection preoperatively.

This study used a test and validation cohort design. In total, over 1,000 patients were included in the analysis. A number of risk factors were identified that are commensurate with other works in the literature. The discriminative capacities of the final models were moderate in nature.

The prognostic utility presented in this work may have the capacity to better identify patients who are at risk of surgical site infection. The number of measures included may make this a cumbersome tool and the fact that this was a single-center study should not lead to surprise that experience in the first cohort was comparable to that of the validation group. Differences in socio-demographic composition or the means by which surgical site infections are diagnosed and treated between this cohort and centers where the results are to be applied may impair translation. As the authors recognize, further validation studies in other clinical settings are necessary. As a result, this study presents Level III evidence.

—The Editors

The prevalence of spinal SSI is reported to be between 0.7% and 12%, depending on the type of the surgery and the studied population [7], [8], [9], [10], [11], [12]. A number of patient- and procedure-specific risk factors have been identified, such as age, diabetes, atrial fibrillation, previous spinal surgery; higher American Society of Anesthesiologists classification, perioperative transfusion, extended procedure, postsurgical incontinence (bowel, bladder, or both), and duration of hospital stay [7], [8], [9]. However, most of these studies focused on specific spine surgery patient groups, such as adults with spinal deformities, and they applied only simplified study designs and analyses. Furthermore, only a few studies reported on the occurrence of SSIs in the general population of spine surgery patients, including those undergoing routine elective procedures. Therefore, a validated presurgical risk estimation of spinal SSIs is important to identify at-risk patients and to reduce risk.

The aim of the present study was to determine the prevalence of SSI, in a cohort of patients after elective routine, primary degenerative lumbar surgeries, and to identify measurable presurgical risk factors. By using a multivariable statistical approach, we built a predictive model, and then we validated it by comparing with data collected from a subsequently studied independent cohort.