Updated: 9/27/2021

Spine Surgical Site Infections

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  • Overview. 
    • Overview
      • postoperative spine infections are a relativley common complication that has the potential to seriously compromise patient outcomes through
        • increased morbidity
        • increased mortality
        • increase reoperation
        • increased hospital stay
        • increased treatment costs
          • estimated to be $200,000 per patient
        • worse overall long-term outcomes
  • Epidemiology
    • Incidence
      • surgical site infection (SSI) general
        • the most common hospital acquired infection that occurs in the early postoperative period
      • spine surgical site infection (SSI)
        • occurs in .7% to 16% depending on type of spine surgery, approach, use of instrumentation, and indication for surgery
        • incidence of SSI in their series following orthopedic spinal operations is 2.0%
        • incidence of some procedures
          • lumbar micodiskectomy
            • with prophylactic antibiotics has a reported 0.7% incidence of infection.
            • use of an operating microscope for diskectomy doubles this rate to 1.4%.
          • lumbar fusion
            • risk of infection is higher with spinal fusion because of the presence of spinal instrumentation
            • in elective surgical instrumented cases, the incidence of infection has been reported to be 2.8% to 6%
          • fracture stabilization/trauma
            • traumatic spine injury has an increased infection risk of up to 10%
              • greater local tissue hypoxia, longer ICU stays, and greater soft tissue damage, catabolic state leading to protein malnutrition, and greater comorbities contribute to increased infection risk
              • risk factors associated with trauma-related SSIs:
                • multilevel spine surgery
                • treatment delay >160 hours
                • complete neurologic deficit
                • severe congnitive impairment
          • anterior vs. posterior
            • posterior spine procedures have a statistically higher incidence of infection postoperatively compared with anterior instrumentation
            • combined anterior/posterior cases do not carry a higher risk of infection than does posterior surgery alone
      • average time to infection
        • 14 months
    • Risk factors
      • medical
        • patient age >70 years
          • may be confounded by older patients having more comorbidities
        • ASA score
        • diabetes mellitus
        • cardiovascular disease
        • malignancy
        • long term steroid use
        • previous lumbar surgery
        • chronic obstructive pulmonary disease
        • immunologic competency
        • prior infection
        • preoperative hospitalization >1 week
        • malnutrition
        • prior radiation
      • lifestyle
        • obesity
        • smoking
        • nutritional status
          • malnourished patients are 15x more likely to develop an infection
        • ETOH
      • intraoperative
        • transfusions
        • use of instrumentation
        • multiple staged interventions
        • amount of levels fused
        • operative room traffic (large number of nurses)
        • surgery lasting longer than 3 hours
        • blood loss >1 L
      • hospital stay
        • duration of patient stay in the postanesthesia care unit
        • prolonged preoperative hospital stay
  • Etiology
    • Pathophysiology
      • pathophysiology
        • instrumentation
          • the use of instrumentation has an important role in the development of postoperative infections
          • can cause local soft tissue irritation leading to inflammation and seroma formation that subsequently provides a fertile breeding ground for microorganisms to grow
          • adherence of bacteria to the surface of implants is promoted by a polysaccharide biofilm called glycocalyx that acts as barrier against host defense mechanisms and antibiotics
          • metallosis from micromotion of the instrumentation leads to granuloma formation and provides yet another medium for bacterial colonization
      • microbiology
        • staphylococcus aureus
          • 73%
          • most frequent microorganism found in spinal SSI is Staphylococcus aureus
          • 5-18% can me methicillin resistant staphylococcus aureus (MRSA)
        • staphylococcus epidermidis
          • increasing frequency in postoperative infections
        • enterococcus coli & enterococcus faecalis
          • patients with incontinence / faecal contamination
        • propio acnes (low virulence microorganisms)
          • patients with compromised immune system could present with surgical wound infected by low virulence microorganisms
          • late hardware infection
        • gram-negative rods
          • generally uncommon cause of SSI
          • trauma patients
            • severe neurologic injury
            • those in an immunocompromised state (injury severity score >18)
          • higher incidence seen with neuromuscular scoliosis patients (cerebral palsy, Duchenne's muscular dystrophy, etc.)
            • higher risk of soiling wound due to poor bowel and bladder control compounded with lack of baseline mobility
        • polymicrobial
          • almost exclusivley a result of direct wound contamination during the post-operative period
          • fecal or urinary contamination of the wound in neuromuscular patients
  • Anatomy
    • Muscles
      • psoas muscle
        • can be site of abscess extension from lumbar discitis
        • presents with hip and thigh pain
    • Ligament
      • anteior longitudinal ligament
    • Blood Supply
      • segemental spinal arteries
  • Classification
    • Anatomic
      • superficial
        • superficial infection are limited only to the skin or subcutaneous tissues without fascial involvement
      • deep
        • deep infections involve the fascia and/or muscle
          • unlikely to respond to the standard 6-week course of antiobiotics alone
    • Chronologic
      • early
        • early, if they occur within 3 weeks of the procedure
      • late
        • more than 4 weeks later
      • latent
        • years after surgery
    • Mechanism
      • direct inoculation
        • contamination during surgery
          • substantial amount of bacteria are needed at the operative site to cause SSI
            • >105 organisms
        • leads to infection within 30 days
      • early posterative (outside-in) contamination
        • drains
        • seroma drainage creating outside-in contamination
        • soiling of wounds
      • late hematogentous contamination
        • dental work
        • foreign infection (UTI)
    • Thalgott classification
      • based on host factors and severity of infection
        • host factors
          • A - normal
          • B - local or systemic disease (smoking, diabetes)
          • C - immunocompromised
        • anatomic factors
          • 1 - single organism (deep or superficial)
          • 2 - deep infection with multiple organisms
            • require an average of 3 irrigation and debridements
          • 3 - deep infection with multiple organisms and myonecrosis
            • very difficult to manage and have poor outcomes
  • Presentation
    • History (optional)
      • night sweats
    • Symptoms
      • wound drainage
        • most common presentation
      • increasing pain
        • increase with time
          • post-op pain should improve with time
      • constitutional symptoms
        • fever is the most common generalized finding with infection
          • temperature >39┬░C is worrisome for a bacterial deep wound infection
      • generalized sepsis
        • generalized malaise
        • lethargy
        • confusion
        • hypotension
        • organ failure is an indication for emergent surgical d├ębridement
          • condition usually presents as generalized malaise, lethargy, and even confusion
    • Physical exam
      • wound
        • wound erythema or discharge common with superficial infections
        • wound may be clean with deep infections
        • drainage
          • persistent draining of a seroma will be clear
          • copious or purulent discharge consistent with infection
      • tenderness
        • over surgical site
  • Imaging
    • Radiographs
      • indications
        • Plain radiographs of the spine are rarely useful for the diagnosis of early infection [8,9,16].
      • findings
        • acute
          • usually normal
        • late & latent
          • loss of disc height
          • end plate erosion
          • lucencies may be present around orthopedic hardware
    • CT
      • indications
        • when concern for the fusion status and implant positioning
      • views
        • best seen on sagital and axial images
      • findings
        • computed tomography scan may show multiple lesions involving the end plates
        • lytic lesions around the screws/implants
        • presence of pseudoarthrosis
    • MRI
      • indications
        • magnetic resonance imaging (MRI) is the most useful study to diagnose SSI [1,8-10,16]
        • magnetic resonance imaging (MRI) is the most useful imaging study, but it must be interpreted with caution
      • technique
        • gadolinium enhancement improves the diagnostic accuracy of MRI and should be used whenever infection is suspected
        • gadolinium enhancement increases the sensitivity of MRI
      • findings suggestive of infection
        • rim enhancement of a large fluid collection is pathognomonic for infection
        • ascending epidural collections
        • evidence of bony destruction
        • progressive marrow changes and ascending epidural collections on MRI scans are also diagnostic of infection
      • sensitivity and specificity
        • inflammatory response following surgery is similar to that seen with infection
    • Bone scan
      • rarely used
      • WBC-labeled may be helpful for identifying and infectious focus
      • indications:
        • patient unable to tolerate MRI (e.g. pacemaker)
  • Studies
    • Serum Labs
      • HgBA1C
        • obtain preop for all diabetic patients
        • should be < 7.0
      • WBC
        • White blood cell count is an unreliable indicator of infection.
      • ESR
        • Erythrocyte sedimentation rate can remain elevated for up to 6 weeks after surgery
        • rising levels after 4th postoperative day can be suggestive of an infection
      • CRP
        • C-reactive protein (CRP) levels normalize within 2 weeks 
        • peaks around post-op day 2
          • persistent high levels or 2nd peak is concerning for infection
        • CRP is a more sensitive indicator of the presence of SSI
        • CRP has been reported to be the most sensitive clinical laboratory marker in assessing the presence of infection and treatment response
          • normalized CRP with improving ESR is suggestive of post-operative SSI resolution
      • Albumin
        • < 3.5 g/DL is concerning for malnutrition
      • transferrin
        • < 150 ug/dl is concerning for malnutrition
    • Cultures
      • superficial skin cultures
        • superficial cultures, whether from the skin or drainage, do not reliably assist with identification of the causative organism
      • aspiration
      • introperative
        • intraoperative tissue cultures remain the gold standard for identification of the causative organism in SSI
          • cultures may be negative in latent infections
            • culturing of removed hardware may yield offending organism due to bacteria "hiding" in the glycocalyx
          • obtained prior to antibiotic adminstration
    • Intraoperative biopsy samples
      • gross anatomy
      • histology/frozen sections
      • immunostaining
  • Differential
    • Key differential (top 4)
      • adjacent segment disease
      • inadequate decompression
      • postoperative seroma
      • postoperative hematoma
  • Treatment
    • Nonoperative
      • oral antibiotics and close observation
        • indications
          • only indicated for mild superficial infections
    • Operative
      • urgent surgical debridement, wound management +/- plastics, ID consult & targeted IV antibiotics
        • indications
          • vast majority of cases
          • any infection that does not respond to antibiotics
          • unacceptable spinal deformity
          • neurologic deficits
          • progression of infection on follow-up MRI studies
        • indications for hardware removal
          • loose hardware
          • refractory infections
          • latent infection and fusion obtained
          • titianium implants are best for use in infection cases
        • indications to retain hardware
          • insufficient stability
            • lack of solid fusion
        • outcomes
          • worse overall long term outcomes compared to index procedure without infection
          • increased treatment costs
  • Techniques
    • Oral antibiotics and close observation
      • technique
        • keflex, bactrim, clindamycin or augmentin
          • choice depends on pathogen of cocern
            • keflex - MSSA
              • keflex 500 mg TID vs. 250 mg QID
            • bactrim - MRSA
            • clindamycin - PCN allergic
            • augmentin - anaerobes
        • local wound care
          • daily dressing changes
          • betadine ointment to surgical wound with dressing changes
    • Urgent surgical debridement, wound management +/- plastics, ID consult & targeted IV antibiotics
      • treatment goals:
        • eradicate infection
        • obtain wound healing
        • maintain mechanical integrity of instumented fixation
        • maintain viability of the bone graft
      • approach
        • uilize prior incision
        • remove necrotic edges of wound
        • should approach down to hardware to avoid disecting into dura
          • extensive scar tissue around dural sac can make determination of dural sac difficult
      • debridement
        • debride tissue in layered fashion
        • pulse lavage with NS +/- antibiotics
      • instrumentation removal
        • remove loose hardware
      • reinstrumentation / extension of instrumentation
        • restore stability of spine
          • upsize existing screws
          • extend proximally if needed
          • consider anterior procedure
      • wound management:
        • multiple debridement if needed
          • remove all devitalized muscle tissue
        • remove all loose bone graft
        • negative pressure wound management
        • dressings and closed suction irrigation systems is becoming more popular in the clinical management of infected wounds to support the wound healing process
        • muscles flaps and local rotational flaps for large soft tissue defects
      • wound closure
        • non-braided suture
        • tension-free closure
          • may require paraspinal muscles flaps with plastic consults
          • may use SPY which helps determine vacularity of wound
      • antibiotic beads
      • drains
        • multiple drains (superficial and deep)
      • wound vac
      • targeted IV antibiotics
        • obtain culture if possible and treat with targeted agents
          • treatment depends on the culture results but generally infections with anaerobes as polymicrobial to be treated with broad spectrum antibiotics, such as vancomycin or metronidazole, administered i.v., for 6 weeks
        • usually require 6 weeks of IV antibiotics
        • obtain PICC line
        • monitor CRP / ESR
        • serial MRI usually not indicated
        • prolonged IV antibiotic therapy can delay hardware removal long enough to allow a solid fusion to occur
  • Complications
    • Wound Complication
    • Pseudoarthrosis
    • Neurologic deficits / paralysis
    • Sepsis
    • End Orgain Failure
    • Death
    • Worse overall outcomes
  • Prognosis
    • Has the potential to seriously compromise patient outcomes
  • Prevention
    • Preoperative (prior to surgical admission)
      • decrease changeable risk factors
        • lifestyle
          • weight loss
          • smoking cessation
          • abstinence from EtOH and drugs
        • medical
          • glucose control
          • address other sites of infection
            • UTI
            • Nasal swaps
              • povidone-iodine swabs for all patients or for MRSA carriers
    • Intraoperative
      • skin preparation (non sterile)
        • shaving
          • clippers preferred over razor
        • isopropyl alcohol
        • surgical prep
      • room sterility
        • proper sterile technique
        • minimize room traffic
        • prepping and draping
      • preoperative antibiotics
        • indications
          • administered within 1 hour of skin incision
          • significantly decrease the incidence of postoperative spinal wound infections
            • some studies suggest may only decrease the severity of the infection
          • should be given before incision and repeated when the operation exceeds 4 hours
        • antibiotic selection
          • no PCN allergy
            • a first-generation cephalosporin (cefazolin most common) is the most commonly used prophylactic antibiotic
              • usually 2g Q8hrs for the first 24 hours
              • 3g Q8hr for obese patients (>100 kg of BMI >35kg/m^2)
          • PCN allergy
            • vancomycin or clindamycin are given to patients who are allergic to cephalosporins
              • vancomycin dosing 1000 mg Q12hrs
                • infusion needs to start >1hr from incision to allow for sufficient tissue levels of antibiotic
              • clindamycin dosing 900 mg Q8hrs
            • patients at risk for MRSA should be treated with prophylactic vancomycin
      • length and complexity of surgery
        • decrease invasiveness of surgery (area of surgical bed)
        • decrease time of surgery
        • decrease blood loss
      • wound antibiotics
        • antibiotic irrigation (holy water)
          • mix with normal saline
        • vancomycin powder
          • The use of powdered vancomycin locally administered during surgery has been associated with reduced SSI rates
            • high local tissue concentrations for several several days post-op
          • vancomycin powder has been linked to increased gram-negative organism infections if they do occur
      • betadine soaks
        • 0.3% betadine soak for 2 minutes
      • frequent release of retractors during procedure
        • at least every 2 hours
        • reduces amount of tissue necrosis at the end of the procedure
      • debridement of necrotic tissue at the end of the procedure
        • muscle tissue that was retracted may become necrotic from pressure necrosis
      • hemostasis
        • seroma and hematoma can subsequently get infected
      • drains
        • evacuates any postoperative hematoma or seroma
        • some studies have not found a difference in SSI with the use of drains
        • the routine use of drains is not recommended after single-level procedures by NASS
      • vacuum-assisted closure
        • dressings/wound vac
    • Postoperative
      • postoperative antibiotics
        • continued postoperatively for no longer than 24 hours

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Questions (3)

(SBQ18SP.14) The use of topical vancomycin powder in open spine surgery would lead to which of the following?

QID: 211256

An increase in overall surgical site infections (SSI)



If infection does occur, a higher rate of vancomycin-resistant SSI



An increased rate of non-union of the fusion site



An increase in infection-related medical costs



If infection does occur, a higher rate of gram-negative SSI



L 4 A

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(OBQ04.122) Which of the following is the most sensitive parameter to detect the increased inflammatory response seen with both postoperative infection and the use of instrumentation in spinal surgery?

QID: 1227

Patient temperature



WBC count



Erythrocyte sedimentation rate



C-reactive protein



Rheumatoid Factor



L 1 C

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Evidence (31)
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