Clinical Outcomes at One-year Follow-up for Patients With Surgical Site Infection After Spinal Fusion

Brian A. Karamian, MD; Jennifer Mao, BS, MBA,Gregory R. Toci, BS; Mark J. Lambrechts, MD; Jose A. Canseco, MD, PhD; Mahir A. Qureshi, BS; Olivia Silveri, BS; Paul D. Minetos, MD, MBA; Jack I. Jallo, MD, PhD; Srinivas Prasad, MD, MS; Joshua E. Heller, MD; Ashwini D. Sharan, MD; James S. Harrop, MD; Barrett I. Woods, MD; Ian David Kaye, MD; Alan Hilibrand, MD; Christopher K. Kepler, MD, MBA; Alexander R. Vaccaro, MD, PhD; Gregory D. Schroeder, MD

Disclosures

Spine. 2022;47(15):1055-1061.

Abstract and Introduction

Abstract

Study Design: Retrospective case-control study.

Objective: To compare health-related quality of life outcomes at one-year follow-up between patients who did and did not develop surgical site infection (SSI) after thoracolumbar spinal fusion.

Summary of Background Data: SSI is among the most common healthcare-associated complications. As healthcare systems increasingly emphasize the value of delivered care, there is an increased need to understand the clinical impact of SSIs.

Materials and Methods: A retrospective 3:1 (control:SSI) propensity-matched case-control study was conducted for adult patients who underwent thoracolumbar fusion from March 2014 to January 2020 at a single academic institution. Exclusion criteria included less than 18 years of age, incomplete preoperative and one-year postoperative patient-reported outcome measures, and revision surgery. Continuous and categorical data were compared via independent t tests and χ ² tests, respectively. Intragroup analysis was performed using paired t tests. Regression analysis for Δ patient-reported outcome measures (postoperative minus preoperative scores) controlled for demographics. The α was set at 0.05.

Results: A total of 140 patients (105 control, 35 SSI) were included in final analysis. The infections group had a higher rate of readmission (100% vs. 0.95%, P<0.001) and revision surgery (28.6% vs. 12.4%, P=0.048). Both groups improved significantly in Physical Component Score (control: P=0.013, SSI: P=0.039), Oswestry Disability Index (control: P<0.001, SSI: P=0.001), Visual Analog Scale (VAS) Back (both, P<0.001), and VAS Leg (control: P<0.001, SSI: P=0.030). Only the control group improved in Mental Component Score (P<0.001 vs. SSI: P=0.228), but history of a SSI did not affect one-year improvement in ΔMCS-12 (P=0.455) on regression analysis. VAS Leg improved significantly less in the infection group (−1.87 vs. −3.59, P=0.039), which was not significant after regression analysis (β=1.75, P=0.050).

Conclusion: Development of SSI after thoracolumbar fusion resulted in increased revision rates but did not influence patient improvement in one-year pain, functional disability, or physical and mental health status.

Introduction

Elective lumbar spine surgery is often performed for the management of pain and functional disability due to spinal stenosis, spondylolisthesis, or disk herniations. The rate of these surgeries has increased 62.3% over the last decade (2004–2015).^[1–5] Surgical site infections (SSIs) are among the most common healthcare-associated complications, with the prevalence of SSI after spine surgery ranging from 0.5% to 18%.^[6–8] SSIs can be superficial (i.e., involving the subcutaneous tissues) or deep (i.e., involving the fascial and muscle layers).^[9] Several factors including advanced age, immunosuppression, operative duration, dependent functional status, spinal instrumentation, and staged procedures have been shown to be associated with an increased risk of postoperative infection after spine surgery.^[8,10–13] Given the morbidity, mortality, and healthcare expenditure associated with SSI, significant focus has been placed on addressing modifiable risk factors including smoking cessation, tight glycemic control, and antibiotic prophylaxis to decrease the risk for adverse outcomes.^[14–18] Patients who develop SSI following spine surgery often have longer lengths of stay, greater risk of reoperation and 30-day mortality, and higher complication rates.^[12]

While adverse surgical outcomes following SSI are well studied, the effects of postoperative infection on patient-reported outcomes remain to be elucidated.^[19,20] Interpretation of previous studies on outcomes after spinal infection is challenging secondary to variability in outcomes assessments, inconsistencies in the definition of infection, and limited sample sizes.^[19–21] As healthcare systems increasingly emphasize the value of delivered care, there is an increased need to understand the clinical impact of SSI on functional disability, pain, and health-related quality of life after spine surgery. The purpose of this study is to compare one-year patient-reported outcomes of patients who did and did not develop SSI after thoracolumbar fusion.

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Table 1. Patient Demographics
	n (%)		P
	Control (N=105)	Infection (N=35)	P
Age (mean±SD) (yr)	64.9±8.16	64.3±9.95	0.847
Sex			0.329
Female	51 (48.6)	21 (60.0)
Male	54 (51.4)	14 (40.0)
BMI (mean±SD) (kg/m²)	33.8±6.14	34.6±6.92	0.566
Follow-up (mean±SD) (y)	2.60±1.64	2.69±1.56	0.695
Diabetes	35 (33.3)	12 (34.3)	1.000
Smoking			0.410
Former	41 (39.0)	13 (37.1)
Nonsmoking	53 (50.5)	21 (60.0)
Smoker	11 (10.5)	1 (2.86)
Race			0.210
Black/African American	6 (5.71)	2 (5.71)
Other	2 (1.90)	3 (8.57)
White	97 (92.4)	30 (85.7)
CCI (mean±SD)	0.83±1.11	0.67±0.78	0.873
ASA (mean±SD)	2.71±0.45	2.74±0.56	0.077
Preoperative diagnosis
Stenosis	94 (89.5)	26 (74.3)	0.051
Spondylolisthesis	64 (61.0)	26 (74.3)	0.222
Deformity	16 (15.2)	3 (8.57)	0.403
Radiculopathy	8 (7.62)	1 (2.86)	0.450
Disk herniation	7 (6.67)	0 (0.00)	0.203
Neurogenic claudication	6 (5.71)	0 (0.00%)	0.337

ASA indicates American Society of Anesthesiologists Physical Status Classification System, BMI, body mass index, CCI, Charlson Comorbidity Index.

Table 2. Surgical Data and Outcomes
	Control (N=105)	Infection (N=35)	P
Levels fused (mean±SD)	1.74±1.29	2.40±2.10	0.133
Procedure [n (%)]			0.375
Anterior	14 (13.3)	7 (20.0)
Circumferential	5 (4.76)	0 (0.00)
Posterior	86 (81.9)	28 (80.0)
EBL (mean±SD) (mL)	433±509	203±326	0.207
Length of stay (mean±SD) (d)	3.63±1.98	4.80±5.52	0.552
Readmission [n (%)]	1 (0.95)	35 (100)	<0.001*
≤30 d	1 (100)	27 (77.1)
31–90 d	0 (0.00)	8 (22.9)
Revision rate [n (%)]	13 (12.4)	10 (28.6)	0.048*

EBL indicates estimated blood loss.
*Statistical significance (P<0.05).

Table 3. Patient-reported Outcome Measures
	Mean±SD		P
	Control (N=105)	SSI (N=35)	P
MCS-12†
Preoperative	44.2±11.6	46.1±9.66	0.501
Postoperative	49.9±10.8	49.9±11.4	0.965
Delta	5.65±13.1	3.80±11.2	0.583
Intragroup P	<0.001*	0.228
MCID [n (%)]	36 (34.3)	7 (30.4)	0.912
PCS-12‡
Preoperative	26.8±9.29	24.1±9.06	0.250
Postoperative	29.9±8.38	31.5±10.8	0.602
Delta	3.06±12.3	7.40±16.0	0.309
Intragroup P	0.013*	0.039*
MCID [n (%)]	27 (25.7)	7 (41.2)	0.243
ODI
Preoperative	49.1±16.5	48.4±17.0	0.606
Postoperative	31.0±15.8	32.8±21.0	0.823
Delta	−18.1±20.1	−15.6±20.8	0.550
Intragroup P	<0.001*	0.001*
MCID [n (%)]	68 (64.8)	21 (60.0)	0.761
VAS Back§
Preoperative	6.95±2.48	6.15±2.66	0.171
Postoperative	3.44±2.60	3.17±2.60	0.602
Delta	−3.52±3.25	−2.98±3.55	0.561
Intragroup P	<0.001*	<0.001*
MCID [n (%)]	80 (76.2)	19 (79.2)	0.965
VAS Leg§
Preoperative	6.84±2.72	5.72±2.80	0.071
Postoperative	3.23±2.99	3.86±2.99	0.357
Delta	−3.59±3.91	−1.87±3.65	0.039*
Intragroup P	<0.001*	0.030*
MCID [n (%)]	75 (71.4)	13 (54.2)	0.163

†N=23 for the SSI group.
‡N=17 for the SSI group.
§N=24 for the SSI group.
*Statistical significance (P<0.05).
MCS-12 indicates Mental Health Component Score; MCID, minimum clinically important difference; ODI, Oswestry Disability Index; PCS-12, Physical Health Component Score; SSI, surgical site infection; VAS, Visual Analog Scale.

Table 4. Multivariate Regression for ΔPROMs
	SSI	P	Age	P	Sex (Male)	P	BMI	P
ΔODI	2.44	0.541	0.12	0.560	2.59	0.472	0.45	0.121
ΔVAS Back	0.68	0.363	0.05	0.178	0.75	0.215	0.09	0.054
ΔVAS Leg	1.75	0.050	0.00	0.952	0.59	0.415	0.03	0.621
ΔMCS-12	−2.23	0.455	−0.04	0.782	−1.17	0.623	−0.26	0.181
ΔPCS-12	4.20	0.212	0.00	0.825	−5.19	0.036*	−0.11	0.601

*Statistical significance (P<0.05).
BMI indicates body mass index; MCS-12, Mental Health Component Score; ODI, Oswestry Disability Index; PCS-12, Physical Health Component Score; PROM, patient-reported outcome measure; SSI, surgical site infection; VAS, Visual Analog Scale.

Table 5. Infections-related Characteristics
Characteristics	n (%)
Duration between surgery and readmission (mean±SD) (d)	22.2±11.7
Description of infection
Deep	31 (88.6)
Superficial incisional	2 (5.71)
Meningitis	1 (2.86)
Disk space	1 (2.86)
Organism
Polymicrobial	14 (40.0)
Monomicrobial	21 (60.0)
Staphylococcus aureus	7 (20.0)
Staphylococcus epidermidis	3 (8.57)
Pseudomonas aeruginosa	4 (11.4)
Escherichia coli	3 (8.57)
Enterobacter cloacae	1 (2.86)
Other*	3 (8.57)
Culture Gram stain type
Negative	15 (42.9)
Positive	14 (40.0)
Mixed	6 (17.1)
Incidence of antibiotic-resistant strains
MRSA	2 (5.71)
VRE	1 (2.86)
Antibiotic duration (mean±SD) (d)	46.2±43.7
Debridement (mean±SD) (n)	1.26±0.61

*Other include Candida albicans, Citrobacter koseri, Enterobacter cloacae, Hafnia alvei, Proteus mirabilis.
MRSA indicates methicillin-resistant Staphylococcus aureus; MSSA, methicillin-sensitive Staphylococcus aureus; VRE, vancomycin-resistant Enterococcus.