Contaminated pedicle screws cost hundreds of thousands of US dollars a year, and through an increase in surgical site infections result in additional and avoidable patient morbidity. Anand Agarwal (University of Toledo, Toledo, USA) and colleagues are calling for a change in the standard of care revolving around implant handling and delivery, cutting costs and improving patient safety.
Less widely recognised is the fact that contamination of pedicle screws still occurs in the sterile field, with intraoperative bacterial contamination needing an urgent solution.
So the issue of contamination is two-fold: outside of the operating room, concerning the reprocessing of pedicle screws, and inside the operating room, when pedicle screws are left exposed on trays and are infected with several common bacterial strains.
Reprocessed pedicle screws still harbour contaminants
Reprocessed pedicle screws have been shown to still have residual microbial and non-microbial contaminants on them. In a study conducted by Aakash Agarwal (Department of Bioengineering and Orthopaedic Surgery, Engineering Center for Orthopaedic Research Excellence, University of Toledo, Toledo, USA) and colleagues, published in the Global Spine Journal, traces of saccharides (including biofilm, endotoxins and fatty tissue), soap residue, and salt residue were identified on six pedicle screws randomly selected from four different trays of cleaned, wrapped and purportedly sterilised implants. In fact, there is evidence that the amount of carbohydrate residue increases following reprocessing. The investigators also found corrosion stains present on the outer surface of the implants.
The screws were retrieved using clean gloves, and immediately placed inside of clean zip-lock polybags before undergoing optical microscopy, scanning electron microscopy with energy dispersive spectroscopy, and Fourier transform infrared spectroscopy.
That reprocessed pedicle screws are not always fully sterile has already influenced policy decisions in some nations. Japan and Scotland have banned the reprocessing of spinal implants used for spinal surgery. The Scottish Health Department said in a statement that repeatedly reprocessing implants in the hospital “is a suboptimal procedure”, following a letter in 2006 from the then chief medical officer for Scotland, Harry Burns.
Burns wrote: “Most orthopaedic units in NHS Scotland use screws, small plates and other small orthopaedic implants which have been repeatedly reprocessed (cleaned and sterilised) by the local Central Decontamination Unit in racks or trays. Concerns have been raised that these implants cannot be properly cleaned, and we have photomicroscopic evidence that they retain or acquire organic and/or chemical residues during reprocessing. Legally, many of these devices are classified as ‘single use’, which means they must not be re-used following contact with a patient, but also that they should only be cleaned and sterilised once, prior to first use. We suspect many of these devices have been recirculating for many years, some perhaps for over two decades. Besides generic concerns over infection and CJD [Creutzfeldt-Jakob Disease] contamination, there is evidence to suggest that reprocessed steel implants can cause inflammatory reactions to a much greater degree than ‘pristine’ devices as delivered by the manufacturer, and there are also issues of corrosion and weakening caused by repeated processing. This has clear implications for reducing implant failures, and we have no option but to address the legal, regulatory and governance issues this practice raises.”
Recent research from Aakash Agarwal and colleagues concurs with Burns, citing multiple issues with conventional reprocessing. Foremost among these is the increased rate of surgical infection. The incidence of surgical site infections in spine surgery is reported in the medical literature as up to 13%. Writing in a separate study also published in the Global Spine Journal, Aakash Agarwal et al write: “Surgical infection is undoubtedly a multifactorial phenomenon with implant handling and clean delivery being only one of these factors [influencing infection rates].” An increased infection rate necessitates longer hospital stays, and may mean that patients are required to undergo reoperations. In addition to the financial and logistical issues this causes, spending a longer time in hospital places an emotional burden on patients. The financial burden of surgical site infections is huge. According to the literature, the average hospitalisation cost for a surgical site infection resulting from orthopaedic surgery is estimated to be US$62,000 per case, at an average frequency of 5.5% of cases.
Speaking to Spinal News International, Aakash Agarwal (Department of Bioengineering and Orthopaedic Surgery, Engineering Center for Orthopaedic Research Excellence, University of Toledo, Toledo, USA), first author on four studies published this year investigating the impact of contamination of reprocessed pedicle screws, explains, “In the first phase, i.e. preoperative contamination, the pedicles screws undergo repeated bulk-cleaning with dirty instruments from the operating room, leading to residue build up at the interfaces and possibly on the surfaces too. This, due to its concealed nature, remains unnoticed by the Sterile Processing Department or other hospital staff.”
However, Aakash Agarwal goes on to note, “These can be avoided by using single-use pre-sterilised screws, which are becoming popular these days, with many countries issuing a ban towards repeated implant reprocessing.”
The second source of contamination is intraoperatively. This may occur, according to Agarwal, if “the sterile pedicle screw shafts are directly touched by the scrub technician with soiled gloves for loading onto an insertion device/screw driver, and is then kept exposed on the working table (either separately or next to the used instruments as the pedicles hole are being prepared).”
In order to avoid this contamination, Aakash Agarwal and colleagues recommend shielding the pedicle screws intraoperatively using a guard. Plastic surgeons and general surgeons have adopted a practice of using an additional layer of barrier against contamination of the implants (Keller’s funnel and wound edge protectors, respectively), and the study investigators suggest it is time for spinal surgeons to follow suit.
Aakash Agarwal argues that this two-step asepsis, involving pre-packaged and pre-sterilised screws, and then a shield, is critical: “Shielding the pedicle screws intraoperatively using a guard provides a superior level of asepsis than currently practiced. All unshielded pedicle screws were carrying bioburden of virulent bacterial species, which provides an opportunity for the development of postoperative infections.”
Many patients undergoing spinal surgery are immune-compromised, and the depth of the screw-bone interface in fusion renders the surgical site fairly inaccessible. Thus, as noted above, it is essential that bacterial contamination is minimised. Pre-sterilised, pre-packaged pedicle screws are still vulnerable to contamination once inside the operating room: during loading, they are touched by technicians, then they are exposed while lying on the tray and while the other pedicle screws are being loaded. Finally, the pedicle screws are touched by the surgeon when being fit checked.
In a study performed by Agarwal and colleagues, 25 pre-sterilised, pre-packaged pedicle screws without a guard were compared to the same number of pre-sterilised, pre-packaged pedicle screws with a guard at four different surgical centres. Following spectroscopy and streaking, it was revealed that there was bacterial contamination in 100% of the unguarded pedicle screws, and a complete absence of contamination in the guarded pedicle screws. In the unguarded screws, which had been preoperatively sterilised in exactly the same way as the guarded screws, 105–107 colony forming units were counted per screw (See image below). The species were identified as Staphylococcus Epidermidis, S. Aureus, S. Pettenkoferi, and Micrococcus Luteus.
Another recent study, by Lukas Leitner (Department of Orthopedics and Trauma, Medical University of Graz, Austria) and colleagues, published in the European Spine Journal, reports that pedicle screw loosening is correlated to chronic subclinical deep implant infection. The investigators conclude: “Chronic implant infection seems to play a role in pedicle screw loosening and ongoing pain, causing revision surgery after spinal fusion. Screw loosening and multiple prior spinal operations should be [grounds for suspicion] suspicious (sic) for implant infection after spinal fusion when it comes to revision surgery.”
While many experts believe the severity of bacterial contamination is underreported, and the ramifications—both in terms of cost and patient safety—are extensive, Agarwal is not alone in calling for a two-step asepsis process to reduce or eliminate bacterial infection at the surgical site.
It should be noted that Aakash Agarwal is director of research and development for Spinal Balance, a company providing sterile and proprietary no-touch orthopaedic implants; Anand Agarwal holds a stock option in Spinal Balance.