Updated: 4/15/2020

Spine Surgical Site Infections

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Introduction
  • 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%.3 
          • 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
  • 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
  • Prognosis
    • has the potential to seriously compromise patient outcomes
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 débridement 
        • 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
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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(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? Review Topic | Tested Concept

QID: 1227
1

Patient temperature

2%

(11/637)

2

WBC count

3%

(19/637)

3

Erythrocyte sedimentation rate

9%

(57/637)

4

C-reactive protein

86%

(547/637)

5

Rheumatoid Factor

0%

(2/637)

L 1 C

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