Overview postoperative spine infections are relatively common and have the potential to compromise patient outcomes through: increased morbidity increased reoperation rates increased length of hospital stay increased treatment costs estimated to be $200,000 per patient worse overall long-term outcomes increased mortality Epidemiology Incidence surgical site infection (SSI) most common hospital-acquired infection that occurs in the early postoperative period spine SSI occurs in 0.7-16% depending on the type of spine surgery, approach, instrumentation, and indication for surgery incidence of SSI following orthopedic spinal operations is 2.0% procedural-dependent incidence lumbar microdiscectomy with prophylactic antibiotics, the reported incidence of infection is 0.7% use of an operating microscope for discectomy doubles the incidence rate to 1.4% lumbar fusion infection risk is higher with spinal fusion due to the presence of spinal instrumentation in elective instrumented cases, infection incidence has been reported to be 2.8-6% fracture stabilization/trauma traumatic spine injury has an increased infection risk of up to 10% greater local tissue hypoxia, longer ICU stays, greater soft tissue damage, increased comorbidities, and induction of a catabolic state leading to protein malnutrition all contribute to increased infection risk risk factors associated with trauma-related SSIs: multilevel spine surgery treatment delay >160 hours complete neurologic deficit severe cognitive impairment anterior vs. posterior approach procedures posterior spine procedures have a statistically higher incidence of infection postoperatively compared to anterior approach procedures combined anterior/posterior cases do not carry a higher risk of infection than solely posterior approach procedures average time to infection 14 months Risk factors medical >70 y/o 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 immunocompromised 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 staged interventions number of levels fused operating room traffic surgery lasting >3 hours blood loss >1 L hospital stay duration of patient stay in the postoperative anesthesia care unit prolonged preoperative hospital stay Etiology Pathophysiology instrumentation instrumentation has an important role in the development of postoperative infections can cause local soft tissue irritation, leading to inflammation and seroma formation that can provide a fertile breeding ground for microorganisms adherence of bacteria to the surface of implants is promoted by a polysaccharide biofilm (glycocalyx) that acts as a barrier against host defense mechanisms and antibiotics metallosis from micromotion of the instrumentation leads to granuloma formation and provides another medium for bacterial colonization microbiology Staphylococcus aureus 73% most frequent microorganism found in spinal SSI 5-18% are methicillin-resistant Staphylococcus aureus (MRSA) Staphylococcus epidermidis increasing frequency in postoperative infections Escherichia coli & Enterococcus faecalis patients with incontinence/fecal contamination Cutibacterium acnes (formerly Propionibacterium acnes, low virulence microorganisms) immunocompromised patients late hardware infection Gram-negative rods generally uncommon trauma patients severe neurologic injury immunocompromised state (injury severity score >18) higher incidence in neuromuscular scoliosis (cerebral palsy, Duchenne's muscular dystrophy, etc.) higher risk of wound soiling due to poor bowel/bladder control compounded with lack of baseline mobility polymicrobial almost exclusively a result of direct wound contamination during the postoperative 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 anterior longitudinal ligament Blood supply segmental spinal arteries Classification Anatomic superficial limited only to the skin or subcutaneous tissues without fascial involvement deep involves the fascia and/or muscle unlikely to respond to the standard 6 week course of antibiotics alone Chronologic early occurs within 3 weeks of the procedure late occurs >4 weeks after the procedure latent years after the procedure Mechanism direct inoculation contamination during surgery substantial number of bacteria are required at the operative site to cause SSI (>10⁵ organisms) leads to infection within 30 days early postoperative (outside-in) contamination drains seroma drainage creating outside-in contamination soiling of wounds late hematogenous contamination dental work UTI, bacteremia, etc. Thalgott classification based on host factors and severity of infection host factors A: normal B: local or systemic disease (including smoking) C: immunocompromised anatomic factors 1: single organism (deep or superficial) 2: deep infection with multiple organisms requires an average of three irrigation and debridement procedures 3: deep infection with multiple organisms and myonecrosis very difficult to manage, and often has poor outcomes Presentation History may report night sweats Symptoms wound drainage most common presentation increasing pain that increases over time postoperative pain should improve over time constitutional symptoms fever is the most common generalized finding temperature >39°C is worrisome for a bacterial deep wound infection sepsis malaise lethargy confusion hypotension organ failure is an indication for emergent surgical debridement Physical exam wound erythema or discharge is common with superficial infections may be clean with deep infections drainage persistent seroma drainage will be clear copious or purulent discharge is consistent with an infection tenderness Imaging Radiographs rarely useful for the diagnosis of early infection findings acute usually normal late and latent loss of disc height endplate erosion lucencies may be present around orthopedic hardware CT indications concern for fusion status and implant positioning views best seen on sagittal and axial images findings may show multiple lesions involving the endplates lytic lesions around the screws/implants presence of pseudarthrosis MRI indications most useful study to diagnose SSI must be interpreted with caution technique gadolinium enhancement improves diagnostic accuracy and should be used when infection is suspected 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 inflammatory response following surgery is similar to the response seen with infection Bone scan indications patients unable to undergo MRI (e.g. patients with a non-MRI-compatible pacemaker) rarely used WBC-labeled scan may be helpful for identifying an infectious focus Studies Serum labs hbA1c obtain preoperatively for all diabetic patients should be <7.0 WBC unreliable indicator of infection ESR can remain elevated for up to 6 weeks after surgery rising levels after the fourth postoperative day can be suggestive of infection CRP levels normalize within 2 weeks peaks around postoperative day 2 persistent high levels or second peak is concerning for infection more sensitive indicator of the presence of SSI has been reported to be the most sensitive clinical laboratory marker in assessing the presence of infection and treatment response normalization of CRP with an improving ESR is suggestive of resolution of postoperative SSI albumin <3.5 g/dL is concerning for malnutrition transferrin <150 μg/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 intraoperative intraoperative tissue cultures remain the gold standard for identification of the causative organism in cases of SSI cultures may be negative in latent infections culturing of removed hardware may yield offending organism due to bacteria "hiding" in the glycocalyx should be obtained prior to antibiotic administration, if possible 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 for mild superficial infections Operative urgent surgical debridement, wound management +/- plastic surgery consult, ID consult, and 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 indications for hardware removal loose hardware refractory infections latent infection after a solid fusion has been achieved indications to retain hardware insufficient stability lack of solid fusion titanium implants are best for infection cases 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 the pathogen keflex for MSSA keflex 500 mg TID vs. 250 mg QID bactrim for MRSA clindamycin for patients with a penicillin allergy augmentin for anaerobes local wound care daily dressing changes betadine ointment to surgical wound with dressing changes Urgent surgical debridement, wound management +/- plastic surgery consult, ID consult, and targeted IV antibiotics treatment goals eradicate infection wound healing maintain mechanical integrity of instrumented fixation maintain viability of the bone graft approach utilize prior incision remove necrotic wound edges dissection should proceed down to the hardware to avoid violating the dura extensive scar tissue around the dural sac can make identification of the dural sac difficult debridement debride in layered fashion pulse lavage with normal saline +/- antibiotics remove loose hardware reinstrumentation / extension of instrumentation restore spine stability upsize existing screws extend proximally if needed consider anterior procedure wound management multiple debridements if needed remove all devitalized muscle tissue remove all loose bone graft negative-pressure wound therapy (NPWT) dressings and closed suction irrigation systems are becoming increasingly popular to support the wound healing process muscle and local rotational flaps for large soft tissue defects wound closure non-braided suture tension-free closure may require paraspinal muscle flaps from plastic surgery consult may use SPY to determine vascularity of the wound antibiotic beads drains multiple drains (superficial and deep) NPWT targeted IV antibiotics obtain cultures and treat with targeted agents treatment depends on the culture results generally, infections with anaerobes are treated as polymicrobial infections with broad-spectrum antibiotics (IV vancomycin or metronidazole) for 6 weeks usually requires 6 weeks of IV antibiotics PICC line monitor ESR/CRP serial MRIs are usually not indicated prolonged IV antibiotic therapy can delay hardware removal long enough to allow solid fusion to occur Complications Wound complications Pseudarthrosis Neurologic deficits/paralysis Sepsis End organ failure Death Worse overall outcomes Prognosis Can seriously compromise patient outcomes Prevention Preoperative decrease modifiable risk factors lifestyle weight loss smoking cessation abstinence from EtOH and substance use medical glucose control address other potential sites of infection UTI nasal swabs povidone-iodine swabs for MRSA carriers Intraoperative skin preparation shaving (clippers preferred over razor) isopropyl alcohol surgical prep room sterility sterile technique minimize room traffic preoperative antibiotics significantly decrease postoperative spinal wound infections some studies suggest they may only decrease the severity of infection administered within 1 hour of skin incision repeated when the operation exceeds 4 hours antibiotic selection no penicillin allergy first-generation cephalosporin (cefazolin most common) usually 2g every 8 hours for the first 24 hours 3g every 8 hours for obese patients (>100 kg or BMI >35 kg/m²) penicillin allergy vancomycin or clindamycin vancomycin dosing 1000 mg every 12 hours infusion needs to start >1 hour from incision to allow for sufficient tissue levels clindamycin dosing 900 mg every 8 hours 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 surgical time decrease blood loss wound antibiotics antibiotic irrigation (holy water) mix with normal saline vancomycin powder powdered vancomycin that is locally administered has been associated with reduced SSI maintains high local tissue concentrations for several days postoperatively vancomycin powder has been linked to increased Gram-negative infections if they do occur betadine soaks 0.3% betadine soaks for 2 minutes frequent release of retractors during the procedure at least every 2 hours reduces tissue necrosis debridement of necrotic tissue retracted muscle tissue may succumb to pressure necrosis hemostasis seromas and hematomas can subsequently get infected drains evacuate postoperative hematomas or seromas some studies have not found a difference in SSI with drain usage NASS does not recommend routine drain usage after single-level procedures vacuum-assisted closure Postoperative antibiotics should only be continued for 24 hours postoperatively