The Urgent Case for Pedicle Screw Guards

A recent level II clinical study published in Clinical Spine Surgery found that current, standard practices in handling pedicle screws for spinal surgery are leading to preventable bacterial contamination.

Aakash Agarwal, Ph.D., of University of Toledo and esteemed colleagues, including world renowned key opinion leaders like Jeffrey Wang, M.D., Neel Anand, M.D., and Steve Garfin, M.D., found that this bacterial contamination can be avoided by utilizing sterile, prepackaged screws with a preinstalled intraoperative guard.

In 2017, a preliminary study conducted at Parkview Hospital, a state-of-the-art facility in Fort Wayne, Indiana, found positive data outcomes with reduced or zero bacterial transmission with screw-guard usage. This led the Center for Disruptive Musculoskeletal Innovation, a research and innovation collaborative center through the National Science Foundation, to approve this multicenter clinical trial on the subject.

Why It Matters

Dr. Agarwal told OTW that this research was inspired by a 2015 study implicating medical glove transmission of infectious organisms from patient skin to wound site during spinal surgery. Agarwal explained, “Their study showed a dramatic reduction in surgical site infection [SSI] rate by renewing the gloves before handing each implant. Around the same time, I joined Spinal Balance’s team who were at the verge of releasing a pedicle screw with a proprietary intraoperative guard. The benefit of the guard was to avoid the need to change gloves again and again, which would require conscious effort on each member of the surgical staff, and would still fail to avoid exposure to open-air and other surfaces or instruments in the ‘sterile-field’”.

Agarwal’s study is titled “A Multicenter Trial Demonstrating Presence or Absence of Bacterial Contamination at the Screw-Bone Interface Owing to Absence or Presence of Pedicle Screw Guard, Respectively, During Spinal Fusion.” Co-authors of the multicenter study were Boren Lin, Ph.D., Ashish G. Agarwal, M.B.B.S., Hossein Elgafy, M.D., Christian Schultz, M.D., Anand K. Agarwal, M.D., Vijay K. Goel, Ph.D., Von Sigler, Ph.D., Chris Karas, M.D., Sandeep Gidvani, M.D., Jeffrey C. Wang, M.D., Neel Anand, M.D. and Steve R. Garfin, M.D.

The authors summarized data on postoperative infections, which are cited in the literature as occurring at the high end of 2-13%. The researchers pointed out that these numbers are underestimated for various reasons. “It is theoretically impossible to irrigate the bone-screw interface post-implantation” and “[c]onsequently, any contamination of pedicle screws before implantation is permanent, and has the potential to cause deep-bone infection, or hardware loosening due to encapsulation of biofilm between the bone and the screw.” This highlights the value of utilizing any possible preventative approaches. Dr. Agarwal and his team also published a literature review, presenting clinical data on the existence of delayed and late onset infection elucidating the long-term implication and uncertainty that arise from encapsulated bacteria.

Current Aseptic Approaches

Antibiotic administration as well as local application of vancomycin powder at the surgical site are commonly used aseptic practices. However, these techniques do not eliminate surgical site infection and present their own concerns. The authors cited recent global task force exploration of how to mitigate overuse of antibiotics, as well as studies showing increased prevalence of microbial infection for patients who received vancomycin powder as concerns.

Method

The researchers used two types of surgical pedicle screws for the study. One group with intraoperative guards, the other without guards. Five independent hospitals with various surgeons and surgical staff produced 31 samples via 28 surgeries for each of the two surgical screw type groups.

For the study, pre-sterilized, individually packaged pedicle screws were employed (with and without guards). During surgery, screws from both groups were first handled by a scrub tech and loaded into a pedicle screw driver within a sterile field. Next, screws were left for 20 minutes on a sterile surgical tray in the operating room. After approximately 20 minutes, the lead surgeon handled the instrument holding the screw to check its fit into the insertion device. Finally, rather than being implanted, the screw sample was taken with fresh, sterile gloves straight into a sterile container without additional handling.

All surgeries were for degenerative or traumatic spine conditions in patients over 18 years old and all standard procedures were kept otherwise. The 3-step protocol utilized in the study was agreed upon by 50 international orthopedic surgeons. They found 20 minutes to be the shortest time of exposure recorded for use of at least one pedicle screw in their daily surgical practices.

While unguarded screws signify those treated with standard practice of removing the sterile packaging, guarded screws by definition maintain impermeable barriers along their length after removal from sterile packaging. These screw guards are removed just seconds before insertion.

The samples were tested via two culturing techniques; streaking and spectrophotometry. Streaking is used to help identify bacteria type. Spectrophotometry measures opacity when light is shined through the specimen. Bacterial growth in such samples would affect this opacity.

After incubating for 24 hours in a Fisher Scientific rotisserie incubator, the turbidity of samples was measured via spectrophotometry. Also, 0.1 mL from each sample were streaked on agar plates with 5% sheep’s blood and incubated at 36 degrees for 14 days, with turbidity and CFU [colony forming units] counts recorded daily. Samples of positive cultures were sent for specific bacterial identification after this time.

Saturated levels of turbidity were detected on screws without guards within 24-48 hours. However, pedicle screw samples with guards showed no turbidity for the entirety of the incubation period. While unguarded screws had visible CFU presence within 2 hours of initial streaking, plates from guarded screws showed no CFU growth during the 14 day incubation period. Bacteria noted were those most commonly found in surgical site infection, staphylococcus and micrococcus.

The authors noted that these outcomes were consistent across the multiple surgical sites included in this multicenter study. Agarwal told OTW, “the most challenging aspect of this study design was the variability inherent in surgical workflow (in a single hospital and between different hospital groups) and making sure that the exact study method is followed in each hospital (especially when many surgical staff rotate and have to be re-trained, so we literally had to train members before each spine surgery on the data collection process). But given the consistency of the methods of exposure in spine surgery, and no change in the existing work-flow due to the use of guard made comparison very easy.”

Implications for Practice

We’ve walked through the science. But why does this matter? What are the implications of these results?

When bacteria is present on screws that are inserted, the contaminants are thus transmitted directly to the patient’s bone at the screw-bone interface. Chronic infection, screw-loosening, pain and need for repeat surgery are all possible ramifications. Sterile pedicle screws with guards showed no bacterial contamination in this research study. The researchers concluded that “This may not eliminate SSI altogether as it is multifactorial in nature, but should be an important precautionary measure against it, or against the subclinical and chronic infections leading to screw loosening and pain.”

Agarwal and colleagues also referenced the study by Rehman and coauthors that showed a marked decrease in SSI rates with surgical glove changes before each handling of pedicle screws. Agarwal and his coauthors created a cost analysis chart comparing additional surgical glove costs to pedicle screw guard production costs for the same number of surgeries and found screw guard costs to be notably lower.

The researchers noted that although vancomycin has become a typical aseptic tool to use topically during surgery, there remains no way to irrigate the screw-bone site itself before surgical closure. The authors summarize that “this study provides multi-center clinical evidence that standard pedicle screw handling techniques lead to contamination of pedicle screws and thereby screw-bone interface. This can be avoided by using a sterile intraoperative guard…This adaptation of an implant guard also appears economic, is achieved without affecting the standard surgical flow or increasing the responsibilities of the surgical staff.”

Dr. Agarwal and his team have just submitted their preliminary data on long-term biofilm formation on pedicle screws from such bacterial encapsulation during surgery. Agarwal said, “We are realizing that many incidences of screw loosening could be a result of biofilm that failed to clinically present as late-onset infection. Previous studies using laboratory culture techniques indicated the presence of bioload in ‘aseptic’ revision surgery. These were considered ‘aseptic’ only because common clinical signs of infection were not present in diagnostics. Our ongoing study, whose preliminary data we just submitted for peer review, is using electron microscopy to capture real-time architecture of the biofilm at the screw-bone interface, in patients undergoing revision surgery.”

Agarwal continued, “Our preliminary data shows that 77% of pseudarthrosis cases presented with loosened explants, and 72% of cases showed biofilm on explants. We also found that areas with biofilm tested negative for calcium phosphate whereas areas without biofilm tested positive for calcium phosphate. In addition, intraoperative swabs of tissue around the screws showed no infiltration of bacteria bioload, and always tested negative, thereby showing the inapplicability of swabbing in cases with intact biofilms. Radiographically there was a halo in most cases (not always though) identifying the loosened implants, and the same implants under electron microscope showed biofilms.”

“This highlights the importance of keeping the implant-bone interface devoid of contaminants via a guard. It also sheds light on the surreptitious dynamics of implant and impregnated microbes, thus explaining the sudden onset of delayed and late infection responses. I would direct scientifically curious readers to an article from Nature by Shiono et al [Sci Rep. 2016;12;6:32758], in which the authors (using a mouse osteomyelitis model) showed that Propionibacterium acnes was absent from the control group (no implants) 6 months after bacterial inoculation, but in the implant group, the bacteria had survived as biofilm around the implant. So if we are going to [do] an implant, we have to guard against the bacteria.”

Agarwal also noted that sterile intraoperative guards are currently being used in the prevention of SSI in international settings. Screw guards are currently cleared in the United States, Europe and Japan, and being clinically used in the U.S. and Japan. In this post COVID-19 period, we all have been reminded of the importance of prevention and vigilance against invisible pathogens, and this level II clinical data sets the story straight for what we need to be doing in spine surgery moving forward.

For more on the modes of pedicle screw contamination and SSI from Agarwal, see OTW’s “Are Your Sterile Implants Really Sterile?”.