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Secondary Infections of the Spine
Summary of Key Points
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Primary infection of the spine is an infection that spreads to the spine hematogenously, whereas a secondary infection is an infection that occurs following spine surgery (i.e., surgical site infection [SSI]).
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SSI is defined as an infection that develops within 30 days after the date of surgery if no implant is left in place or within 365 days if an implant is in place.
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SSIs can be classified as superficial (i.e., suprafascial) or deep (i.e., subfascial), and acute (develops within 3 weeks of procedure) or chronic/delayed (>4 weeks after procedure).
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Risk factors for spinal SSI include American Society of Anesthesiologists score greater than 2, diabetes mellitus, obesity, body mass index, previous spine surgery, smoking, urinary tract infection, hypertension, transfusion, cerebrospinal fluid leak, dural tear, blood loss, prolonged operative time, and prolonged hospital stay.
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Careful perioperative risk management is key in preventing SSI.
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Patients can present with pain, wound complications (e.g., drainage, delayed healing), constitutional symptoms, new neurological deficits, spinal instability/deformity, and/or sepsis.
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Workup of SSI includes labs (complete blood count with differential, erythrocyte sedimentation rate, C-reactive protein, blood cultures), imaging (x-rays, computed tomography [CT], magnetic resonance imaging), and biopsy (CT-guided or intraoperative).
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The gold standard treatment for spinal SSI is debridement followed by targeted antibiotic therapy.
Spinal infection includes infections of the intervertebral disc, termed spondylodiscitis or septic discitis, infection into the end plates or vertebral body, termed vertebral osteomyelitis or spondylitis, and epidural abscess in the spinal canal. Infection of the spine can be primary or secondary. Primary infection arises from the hematogenous seeding of bacteria to the spine, whereas secondary infection is the result of direct trauma, injection, or surgery. This chapter reviews the diagnostic workup and management of secondary infection of the spine, specifically focusing on postoperative spinal infection (i.e., surgical site infection [SSI]).
The Centers for Disease Control and Prevention defines SSI as an infection that develops within 30 days after the date of surgery if no implant is left in place or within 365 days if an implant is in place. SSI can be further classified based on the anatomical location or duration from the date of surgery ( Table 45.1 ). Superficial infections only affect the skin or subcutaneous tissues (i.e., suprafascial), whereas deep infections involve the deep soft tissues, including fascia and muscles (i.e., subfascial). Acute SSI is an infection that develops within 3 weeks of the procedure, whereas delayed or chronic SSI is an infection that develops more than 4 weeks after the procedure.
TABLE 45.1
Classifications of Surgical Site Infection
| Location | Superficial: infection involves skin or subcutaneous tissues (i.e., suprafascial) Deep: infection involves deep soft tissues including fascia and muscles (i.e., subfascial) |
| Duration | Acute: infection develops within 3 weeks of procedure Chronic or delayed: infection develops more than 4 weeks after procedure |
SSI is a dreaded complication among spine surgeons, as it increases health care cost, prolongs hospitalization, and often requires readmission and reoperation for definitive management. The incidence of spinal SSI varies significantly depending on several important factors, including case complexity, surgical approach, implant use, primary versus revision surgery, and open versus less invasive techniques. As expected, SSI is rarest (0.5%) after lumbar microdiscectomy and is more prevalent (5.2%) after adult spinal deformity correction. In a comprehensive evaluation of 108,419 procedures submitted to the Scoliosis Research Society Morbidity and Mortality database, there was an overall total infection rate of 2.1% (0.8% superficial, 1.3% deep).
In addition to its systemic effects, SSI can cause pseudoarthrosis, intractable pain, neurological compromise, and death. Although infection is an inherent potential complication of any surgery, early recognition and appropriate management of spinal SSI are essential to improving clinical outcomes.
Risk Factors
SSI of the spine is associated with both modifiable and nonmodifiable patient risk factors ( Table 45.2 ). Patients with systemic diseases such as cardiac, pulmonary, or renal comorbidities have increased risks for developing SSI following spine surgery. Smoking is a well-established risk factor for spinal SSI. , Nicotine specifically decreases tissue oxygenation and attenuates the inflammatory response, therefore delaying wound healing. Meng et al. identified 12 risk factors for spinal SSI: American Society of Anesthesiologists (ASA) score greater than 2, diabetes mellitus (DM), obesity, body mass index (BMI), previous spine surgery, smoking, urinary tract infection (UTI), hypertension, transfusion, cerebrospinal fluid (CSF) leak, dural tear, and blood loss. Interestingly, gender, age, alcohol use, and steroid use were not found to increase the risks for SSI in their metaanalysis. Other independent risk factors have also been reported, including chronic obstructive pulmonary disease, coronary artery disease, osteoporosis, the presence of 10 or more people in the operating room, prolonged operative time, and prolonged hospital stay.
TABLE 45.2
Risk Factors for Surgical Site Infection
| Meng et al. (2015) | Koutsoumbelis et al. (2011) | Lim et al. (2018) | Zhang et al. (2018) | |
|---|---|---|---|---|
| Study design | Metaanalysis | Retrospective case-control | Retrospective multivariate analysis | Metaanalysis |
| Patient-associated factors | ASA score >2 Diabetes mellitus Obesity Body mass index Previous spine surgery Smoking Urinary tract infection Hypertension |
Obesity Diabetes Mellitus COPD CAD Osteoporosis |
Obesity ASA score >2 |
Female sex Diabetes Obesity BMI Hypertension Previous surgery |
| Surgeon-associated factors | Transfusion CSF leak Dural tear Blood loss |
Estimated blood loss ≥10 people in OR Dural tear |
Operative time >6 hours | Prolonged operative time Prolonged hospital stay |
ASA , American Society of Anesthesiologists; COPD, chronic obstructive pulmonary disease; CAD, coronary artery disease; BMI, body mass index; CSF, cerebrospinal fluid; OR, operating room.
As previously mentioned, surgical approaches (i.e., anterior, posterior, or combined) and techniques (i.e., open or minimally invasive) play an important role in the development of postoperative spinal infection. Would healing is more favorable when the approach goes through well-defined soft tissue planes (e.g., Smith-Robinson approach), because this causes less muscle disruption and better preserves local tissue vascularity. For those reasons, in the cervical spine, posterior cervical surgery poses higher risks for SSI than anterior cervical surgery. Likewise, the rates of SSI are reportedly lower after minimally invasive surgery compared with traditional open spinal surgery, specifically for lumbar microdiscectomy and transforaminal lumbar interbody fusion. , Spinal fusion surgery, which requires a wider surgical exposure and prolongs operative time, and implant use, which is prone to bacterial adherence and development of a biofilm, are additional risks factors for SSI. Finally, revision spine surgery has a higher incidence of SSI compared with primary spine surgery.
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