Infections in Spine Surgery: The Role of Occult Pathogens

Highlight from the North American Spine Society 32nd Annual Meeting

Experts gathered to discuss current research on occult pathogens linked to infection in spinal surgery and possibly failed back surgery in a symposium titled, What Lurks Beneath? Understanding Link Between the Presence of Occult Pathogens and Failed Surgery—What is the Prevalence and What Should We Do? at the recent North American Spine Society (NASS) 32nd Annual Meeting. In addition, the experts discussed sources of contamination, as well as evidence supporting strategies to reduce infection rates, including novel advances in implant surfaces designed to limit biofilm formation.
Bacteria Staphylococcus aureus MRSA on the surface of skin or mucous membrane, 3D illustrationStaphylococcus aureusImplant infection is one of the most serious complications of spine surgery, and has high associated costs. In a recent literature review, the average rate of surgical site infection in select spine surgery was 1.9%, and was higher (3.8%) for surgeries involving instrumented spinal fusion, explained Celeste Abjornson, PhD, Director of the Integrated Spine Research Program at the Hospital for Special Surgery in New York City.1

Pre-operative antibiotic infusions are used to target bacteria detecting before surgery, and antibiotics are given prophylactically prior to closing to prevent infection. “However, some bacteria show antibiotic resistance, and it has been reported that almost 80% of bacteria show resistance to at least one antibiotic,” Dr. Abjornson said. “Moreover, when administered systemically, you have to give large amounts [of antibiotics] in order to treat locally.”

Dr. Abjornson focused on occult, indolent infections that result from contamination or are innate. She noted that the intradiscal space, in particular, may be susceptible to indolent infections as it is a physiologically tenuous environment in terms of oxygen tension, pH, and vascularity. In addition, environments created by adding hardware to the body may lead to biofilm development, which is another source of occult infection in spinal surgery. The role of these indolent infections in failed surgeries is currently the topic of research, given that up to 30% of patients who undergo discectomy report chronic pain post-operatively, according to Dr. Abjornson.

Innate Infection
Dr. Abjornson presented data from two studies showing innate infection in patients undergoing microdiscectomy. In the first study, excised disc material from 52 patients undergoing primary lumbar microdiscectomy showed positive cultures in 10 patients (19.2%), with Propionibacterium acnes (P. acnes) being the most common pathogen. None of the patients had diabetes, were taking systemic steroids or chemotherapy, were immunocompromised, or had undergone prior lumbar surgery and, thus, would not be expected to have underlying infection, Dr. Abjornson explained.2

In the second study, 40% of patients (115/290) undergoing lumbar microdiscectomy for symptomatic lumbar disc herniation had P. acnes in disc tissue samples. Other patients’ samples had coagulase-negative staphylococci (11%) and alpha-hemolytic streptococci (3%).3

“Clearly, P. acnes can survive in the nucleus pulposus,” Dr. Abjornson said. In the case of a herniated disc, bacteria such as P. acnes could escape into the intradiscal space with the nucleus pulposa or could move up into the vertebral body, she added.

Biofilm
While biofilm often is thought of as inert, it can be a harbinger of bacteria and can lead to loosening of instrumentation, and potentially fusion failure in spine surgery, Dr. Abjornson explained. In fact, up to 65% of the bacterial infections are caused by these biofilm-producing organisms.3

Biofilms can be composed of a single organism or can be polymicrobial, with Staphylococcus aureus and Staphylococcus epidermidis being the most common biofilm-forming bacteria in orthopaedic implants.5 P. acnes also has been commonly found in biofilm, Dr. Abjornson said.

Thus, “we need to design surfaces to control or eliminate biofilms,” Dr. Abjornson told the audience. “There is a lot of push towards this with 3D printing and different types of coatings, that reduce biofilm and allow for better bony integration to reduce aseptic loosening and occult infections.”

Titanium Coating, 3D Printing, and PEKK
Titanium coated instrumentation is one strategy that reduces the biofilm layer. Unlike polyetheretherketone (PEEK), which is hydrophobic and creates a biofilm layer, instrumentation with titanium coating are hydrophilic and eliminate the biofilm layer when roughened or produced with a poor depth that is favorable to cell proliferation, Dr. Abjornson said.

This relatively new technology is quickly being outdated by 3D printed surfaces that do not form a biofilm layer when coupled with a surface coating, she noted.

Another recent advancement is the approval of the first polyetherketoneketone (PEKK) device. “By switching out the ethylene group [as in PEEK] to a ketone group, you change the protease and intrinsic properties making it hydrophilic instead of hydrophobic,” Dr. Abjornson said. “It is still a 2D printed type of surface at its core, but it can be 3D printed.”

PEKK has an elastic modulus similar to bone and results in bone integration all around the implant, because the hydrophilic nature of PEKK soaks in to some degree, Dr. Abjornson explained. In contrast, both titanium coated and non-coated PEEK show less integration of bone, as demonstrated in a histologic image presented by Dr. Abjornson.

“This is a huge advancement for polymer in the field of orthopaedic implants. And I think that we will see more PEKK as the years continue,” Dr. Abjornson said.

Other presentations related to this symposium:

Disclosures
Dr. Abjornson disclosed the following relationships: Consulting: Woven Orthopaedics, Paradigm Spine, Centinel Spine; Speaking and/or Teaching Arrangements: DePuy Spine; Research Support: investigator salary: Orthobond, NuTech Spine, Vertical Spine, Bacterin, NovaBone; Research Support: DePuy Synthes.

Updated on: 01/08/18
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