Do Occult Pathogens Play a Role in Failed Back Surgery?

Highlight from the North American Spine Society 32nd Annual Meeting

Occult pathogens may play a role in chronic pain and failed fusion in instrumented spine surgery, said Antonio T. Brecevich, MD, at the NASS 2017 session, What Lurks Beneath? Understanding Link Between the Presence of Occult Pathogens and Failed Surgery—What is the Prevalence and What Should We Do? The impact of this potential association is marked given the rising rates of instrumented spinal fusions in the past decade.
Thoracolumbar instrumentation: rods and screwsWhile surgical site infections are relatively rare, the risk is higher with instrumentation use depending on the type of surgical procedure.Dr. Brecevich specified that failed back surgery is somewhat of a misnomer, and used the term to indicate chronic pain following previous spine surgery in patients whose blood test results are within normal limits and without instrumentation malfunction. Dr. Brecevich is a spine research fellow at the Hospital for Special Surgery in New York City.

While surgical site infections are relatively rare, the risk is higher with instrumentation use (0.7% to 11.9% depending on the type of procedure), Dr. Brecevich said. These infections are a significant concern as they can lead to longer and costlier hospitalization. In addition, the reported incidence of delayed infection after instrumented spine surgery (ie, 6 months after the index procedure) is reported to be between 0.2% and 6.9% in the literature, but is likely to be underreported, he said.1-3

One of the most common organisms detected in surgical site infections is Propionibacterium acnes (P. acnes), which is present in up to 95% of healthy human skin, Dr. Brecevich said.

As discussed in an earlier presentation, the formation of biofilm on instrumentation used in spine surgery could lead to micromotion, loosening of instrumentation, and possibly to fusion failure. While mechanical nerve compression or loose instrumentation may be the culprit of failed back surgery, the possibility of occult infection needs to be included in the differential diagnosis, Dr. Brecevich noted.

High Rate of Infection Found in Revision Spinal Fusions
To better understand the incidence of occult pathogens in instrumented spinal fusions, Dr. Brecevich and colleagues from the Hospital for Special Surgery prospectively studied 50 consecutive patients undergoing revision surgery whose index spine procedure included pedicle screw instrumentation.4 The mean interim period between the index procedure and revision procedure was 4.6 years, and ranged from 6 months to 21 years.

None of the patients were positive for markers of infection on pre-operative blood tests (ie, erythrocyte sedimentation rate, C-reactive protein, and white blood cell count). Perioperative antibiotics were held until instrumentation was removed.

Each piece of instrumentation and surrounding tissue at the operated level were evaluated using an extended 14-day culture. Occult adherent bacteria were found in 38% (19/50) of the removed tissue/instrumentation. Polymicrobial infections were found in 26% of patients (5/19).

“We were able to identify 8 distinct and different species of bacteria, the most prevalent of which was P. acnes at 58%,” Dr. Brecevich said. The average time to identification was 5 days, which is notable given that the standard culture protocol is 3 days, he said.

Histological analysis was consistent with positive cultures from microbiology and confirmed the presence of chronic inflammation (eg, dead collagen, fibrous tissue, and neutrophil granulocytes). Significant predictors of a positive culture were male gender (P=0.01) and higher body mass index (P<0.05).

One important limitation of the findings is that a lack of an applicable control group.

“By not culturing the instrumentation of patients not experiencing pain, we cannot confirm that the presence of occult pathogens as the causative factor of chronic pain, pseudarthrosis, or failed fusion surgery,” Dr. Brecevich said.

Similar findings were reported in a retrospective review by Lieberman et al presented at NASS 2017.5 Positive cultures were found in removed instrumentation and/or surrounding tissue culture from 15 of 162 consecutive patients (9.3%) who underwent revision spine surgery. The most common organisms identified were P. acnes (46.7%) and Staphylococcus (40.0%).

Spine Surgeons Need a High Index of Suspicion for Occult Pathogens
“Long-term cultures are vital for identifying occult pathogens,” Dr. Brecevich emphasized. “We need further research to investigate the relationship between these occult pathogens and bone formation at that bone-implant interface. Surgeons need to have a high index of suspicion for the presence of occult pathogens … and there needs to be a patient care algorithm sensitive to identifying occult pathogens, which will require significant collaboration with microbiology departments,” he concluded.

Other presentations related to this symposium:

Updated on: 01/08/18
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