Total joint replacement surgery is becoming common, with more than 600,000 such procedures per year carried out in the United States alone. It is expected that this demand will continue to grow. The success rate of such arthroplasties has greatly improved over the past 20 years, and the failure rate varies, depending for example, on the type of arthoplasty, design of the implant, and age of the patient. A recent study reports that for total hip arthroplasties, the revision rate at 5 years was 2.7% and at 7 years was 3.4%.1
A recent review of 1,366 hip replacement surgeries2 indicated that the most common cause of this type of primary implant failure was aseptic loosening of the implant (in 51% of the cases); whereas infection only accounted for 8% of primary failures. When the primary failed hip was replaced (revision hip arthroplasty), the failure rate was approximately 20%. The most common cause of failure of the revision was infection (30.2%) and aseptic loosening accounted for 19.4% of failures.2
Aseptic loosening occurs when the host mounts an inflammatory response composed of T-cells, macrophages, and giant cells,3–7 resulting in lack of osseointegration and loosening of the implant. The origin of aseptic loosening has been studied for many years and the role of organic residuals on screws and plates prior to implantation has been suggested as a possible source for antigenic material that may stimulate the inflammatory response.2–10
Bonsignore et al. (2011) demonstrated that endotoxin and possibly other contaminants on implants impaired osseointegration, and led to loosening of the implant in their mouse model.8 Furthermore, they observed that this effect did not occur with rigorous cleaning methods (alkali ethanol and 25% nitric acid), but did with routine autoclaving. They clearly documented that adding endotoxin back to the rigorously cleaned implants restored the inflammatory response that led to loosening.8 This supports earlier studies by Bi, Xing and colleagues, who also showed that endotoxin, along with wear particles, caused inflammatory reaction and loosening of implants in mouse models.3–6
The racks that hold the screws are not designed to facilitate optimal cleaning of the screws; rather, they are designed to facilitate presentation of the screws to allow the surgeon to easily select the size needed.
This is particularly relevant in the United States, because in most North American healthcare facilities, small implantable screws and plates within most manufacturers' orthopedic tray sets are reprocessed along with reusable instruments in the surgical tray set. Figure 1 is just one example of many possible configurations of stainless steel or plastic trays and racks produced by manufacturers. The racks that hold the screws are not designed to facilitate optimal cleaning of the screws; rather they are designed to facilitate presentation of the screws to allow the surgeon to easily select the size needed. The screws are seated in racks in such a manner that cleaning fluids have limited access to the underside of the rack. As a result, when the rack is processed through an automated washer, cleaning and rinsing of each individual screw is challenging.
In a recent study, we reported that extremely high levels of endotoxin (lipopolysaccharide) were found on plastic surgery instruments that had been cleaned using an automated washer (with an average of 25,373 endotoxin units or EU/cm2 found on skin hooks).11 We concluded that the endotoxin originated from the final deionized water rinse, and suggested this was most likely derived from biofilm that developed in the DI tank, as there is no chlorine in this water to inhibit microbial growth.
The ability of endotoxin to retain biological activity despite steam sterilization is well known, and Bonsignore's study showed that implants with endotoxin still stimulated an inflammatory response when implanted in mice despite having been autoclaved.8 The endotoxin levels on the implants evaluated by Bonsignore (up to 50 EU/m2) are much lower than the levels of up to 25,000 EU/cm2 we found on plastic surgery instruments post cleaning.11
Defining the Problem
Of concern is whether the instrument manufacturers have validated that the screws and plates within the orthopedic surgical tray sets can be safely cleaned and steam sterilized hundreds of times. These items are considered “single use,” and are sometimes provided by the manufacturer in separate sterile packages. Indeed, in Australia and Scotland, there have been reports prepared to address this specific problem and in both instances the recommendation was to use single-use, presterilized, and individually wrapped screws and plates.12–13
In Scotland, the deadline for conversion of all orthopedic units to prepackaged, sterile, single-use implants was Dec. 31, 2007. As pointed out by the Scottish Health Department, “most orthopedic units in the [National Health Service] of Scotland use screws, small plates and other small orthopedic implants which have been repeatedly reprocessed (cleaned and sterilized) by Central Decontamination Units in racks or trays…We suspect many of these devices have been recirculating for many years.” With respect to dealing with existing stocks of screws and plates, they stated that “using up old stock would simply prolong what we now recognize as suboptimal clinical practice.”12
Despite steps being taken to address this issue in countries such as Scotland, it remains common practice in North America to have screws and plates as part of the instrument tray set that are reprocessed every time that the instrument tray set is reprocessed. Furthermore, it is difficult to determine how often these implantable items have been reprocessed in either site-owned or loaner instrument tray sets. Currently there is no way to track each screw and plate to know how many times they may have been reprocessed prior to being implanted. This issue is common to virtually all the orthopedic surgical tray sets from all manufacturers.
The objective of the current study is to critically assess the instructions for use (IFU) from seven surgical-tray-set manufacturers who provide screws and plates in tray sets to healthcare facilities in North America, and to outline the confusion that exists around this issue. Finally, we provide some practical suggestions for manufacturers and healthcare reprocessing staff that may be helpful in the interim, until regulatory agencies in North America provide guidance on this issue.
The ability of endotoxin to retain biological activity despite steam sterilization is well known.
Analysis of Manufacturer IFU
Table 1 summarizes and compares the clarity of the IFU from seven different manufacturers. Only two of seven clearly indicated that screws and plates are implantable items, and that the manufacturer has validated the cleaning process for these items. Of these two, one IFU instructs that the rack of screws should remain in the tray set for cleaning in the automated washer. The second requires “devices” to be removed from the tray set for cleaning, but it is unclear whether this applies to the rack of screws, and if so, what cleaning (if any) should be performed for screws.
The term “single-use” is used in all seven of the IFU, with clear instructions that such items should not be reprocessed if they come into contact with the patient, or are visibly soiled with patient material. It is unclear in five whether screws and plates are “single-use,” whether they are to be cleaned and sterilized only once (as for some implantable prostheses), or whether they can be safely reprocessed multiple times.
It is apparent that none of the IFU from the seven manufacturers clearly state whether the screws, plates, or other small implants can be indefinitely reprocessed, or whether there are a limited number of times they should be reprocessed (see question 6, Table 1). All seven recommend that ultrasound be used as part of the cleaning process, but none clearly state whether this applies to the racks of screws or plates that are implantable.
The majority of the current IFU used in North American healthcare facilities do not clearly address the reprocessing of implantable items such as screws and plates.
The seven IFU clearly indicate that high purity water should be used for the final rinse, but there are no recommendations regarding facility monitoring of the quality of rinse water. Although not a requirement, it may be helpful if IFU refer to AAMI TIR34,14 which does provide guidelines for monitoring high purity water to ensure that excessive microbial or endotoxin levels are not present. All seven IFU also clearly indicate that users must validate the on-site cleaning efficacy, but there is no indication of how this is to be achieved.
From this review of the IFU from seven manufacturers of orthopedic surgical tray sets, it is apparent that the majority of the current IFU used in North American healthcare facilities do not clearly address the reprocessing of implantable items such as screws and plates. North American reprocessing personnel are therefore faced with a “Pandora's Box” dilemma.
These items are conveniently placed within the instrument tray set, and even if they are supplied as individually wrapped sterile items, site staff may remove the wrapping and place devices in the tray set racks, as these provide a convenient presentation of sizes in the surgical field. However, processing these devices in this way can create no end of reprocessing problems and risk for the patient.
If the IFU does not have clearly validated instructions for implantable screws and plates, but reprocessing these is a widespread practice, what should SPD personnel do? The detailed approach outlined by the Scottish Health Department13 is helpful, acknowledging operational issues and outlining practical solutions. Based on these instructions and the published data, some practical recommendations for North American healthcare reprocessing personnel and implant manufacturers have been summarized in the accompanying sidebars.
There is sufficient published data to support the concept that organic residues on implantable items do elicit inflammatory responses that cause loosening of implants in animal models. Furthermore, published data indicates that there may be organic residues that accumulate on small implantable items such as screws and plates that are reprocessed numerous times in orthopedic surgical tray sets. Whether these organic residuals are the basis for the aseptic loosening that is the most common cause of joint arthroplasty failure in humans has yet to be conclusively proven.
More research is needed to confirm that small implants currently in use have accumulated organic material, and that this contributes to aseptic loosening. In addition, our review of seven IFU provided by manufacturers demonstrates that they do not clearly identify what should be done with the small implantables such as screws and plates present in orthopedic tray sets. It is also not clear if validated cleaning processes are available that can be used for repeatedly reprocessed small implantable devices. To solve this “Pandora's Box” dilemma will require changes on many levels, and meaningful progress will only be possible if there is shared responsibility by all stakeholders.
Ensure that IFU clearly address the issues outlined in Table 1, and take into consideration the FDA's guidance for manufacturer's regarding instructions for reprocessing of reusable medical devices.15
If screws and plates have not been validated for reprocessing and should be sterilized only once, then this should be clearly stated in the IFU, and on the device and packaging.
As outlined in the Scottish Health Department letter of 2007,13 manufacturers should work with surgeons, operating room nurses, and reprocessing personnel to find a way to ensure screws and plates can be presented in the surgical field conveniently, but also address items that are single-use and cannot be reprocessed.
Require the manufacturer to provide validated cleaning instructions that clearly state whether implantable screws and plates can be reprocessed or not. If the IFU does not contain this information, then request that the manufacturer provide a letter specifically stating what they recommend for their screw and plate implants.
Ensure that personnel are adequately trained, so that manufacturer IFU is properly followed.
Ensure that sterile packaged screws labeled as “single-use” are not removed from their sterile packaging and used to restock racks of screws in surgical tray sets.
During surgery, require surgeons to remove screw and plates from surgical tray sets using sterile forceps, thereby avoiding contamination of other implantable items in the tray set with blood or tissue that may be on the surgeon's gloves.
Ensure that the final rinse water used for cleaning of surgical tray sets is high quality, to reduce the risk of water impurities being left on the implantable screws and plates after the final rinse. In addition, train personnel to ensure water quality is routinely monitored, as outlined in AAMI TIR34.14
About the Author
Michelle J. Alfa, PhD, FCCM, is professor in medical microbiology at the University of Manitoba, and clinical microbiology medical director at Diagnostic Services of Manitoba. E-mail: firstname.lastname@example.org