|Year : 2022 | Volume
| Issue : 3 | Page : 16-23
The influence of pin material and coatings on the incidence of pin site infection after external fixation
Samson Arveladze1, Fintan Moriarty1, Toby Jennison2
1 AO Research Institute Davos, Davos, Switzerland
2 Department of Orthopaedics, Cardiff and Vale University Health Board, Wales, United Kingdom
|Date of Submission||21-Nov-2021|
|Date of Decision||28-May-2022|
|Date of Acceptance||03-Aug-2022|
|Date of Web Publication||12-Oct-2022|
Cardiff and Vale University Health Board. University Hospital Wales, Heath Park, Cardiff CF14 4XW
Source of Support: None, Conflict of Interest: None
Introduction: External fixation is used for a wide variety of surgical treatments. The transcutaneous pins used in external fixation, however, provide a route for bacterial migration from the external to subcutaneous space, and high rates of pin site infection have been reported. The material of which the pin is composed, or any surface coating that is applied, may significantly influence tissue integration and pin site infection. However, clinical data are scarce. The aim of this systematic review and meta-analysis was to summarize the clinical evidence for the role of pin material, and surface coatings, on the incidence of infection at external fixator pin sites. Materials and Methods: A systematic review was performed following registration with PROSPERO. A search was performed using Medline, Embase, and Cochrane. Inclusion criteria were (1) recorded diagnosis of infection, (2) involved external fixation, (3) any bone, (4) English language, (5) human subjects, (5) pin material known, and (6) all levels of evidence. All stages of the review process were performed by two independent reviewers. A meta-analysis was performed using a random effects model meta-analysis to produce odds ratios. Study bias was assessed using the Cochrane risk of bias tool Rob II. Strength of evidence was based on the American Academy of Orthopaedic Surgeons methodology for defining the strength of recommendation. Results: After exclusion, 8 studies were further analyzed. One study compared stainless steel and titanium with an odds ratio of 1.00 (95% confidence interval [CI]: −0.70–2.70). Three studies compared stainless steel to hydroxyapatite (HA)-coated pins with an odds ratio of 0.25 (95% CI: −0.52–1.02). Two studies analyzed titanium compared to HA-coated pins with an odds ratio of 1.12 (95% CI: −4.25–6.48). Two studies analyzed silver compared to stainless steel with an odds ratio of 0.12 (95% CI: −0.89–1.12). However, the strength of evidence was limited for all studies. Overall, 0 studies had a low risk of bias, 4 studies had an unknown risk of bias, and 4 studies had a high risk of bias. Conclusion: There is currently limited evidence of the effect of different pin material or coatings on the incidence of pin site infection, with the available studies showing contrasting results. Further high-quality and adequately powered studies are required to provide definitive guidance.
Keywords: External fixation, hydroxyapatite, infection, pin tract, silver, stainless steel, titanium
|How to cite this article:|
Arveladze S, Moriarty F, Jennison T. The influence of pin material and coatings on the incidence of pin site infection after external fixation. J Limb Lengthen Reconstr 2022;8, Suppl S1:16-23
|How to cite this URL:|
Arveladze S, Moriarty F, Jennison T. The influence of pin material and coatings on the incidence of pin site infection after external fixation. J Limb Lengthen Reconstr [serial online] 2022 [cited 2022 Dec 9];8, Suppl S1:16-23. Available from: https://www.jlimblengthrecon.org/text.asp?2022/8/3/16/358264
| Introduction|| |
External fixators are used for a wide variety of procedures including acute fractures, revision after bone infection, and limb lengthening. External fixators can remain in situ for several months, and since the transcutaneous pins provide a direct communication between the bone and the external environment, there is a constant risk of developing infection. Pin site infection has been reported in up to 70% of cases,, with the most common causative organisms being Staphylococcus aureus and Staphylococcus epidermidis, although the literature on the topic remains limited. There has been considerable research into pin site dressings and care to reduce the risk of infection, but there remains no consensus on the optimal protocol.,, Once diagnosed, pin site infections can often be successfully treated with oral antibiotics, but can also develop into deep infections with osteomyelitis requiring debridement and removal of the pin.
The development of pin site infection is a multifactorial process. The ability of bacteria to adhere to the surface of the pin, and for the local soft tissues to integrate with the pin are crucial factors. A significant amount of basic science research has been performed on modifications to implant surfaces to minimize bacterial colonization and control tissue integration. Comparative studies of pin materials have been performed in both in vitro and in vivo settings.,, The most commonly used pin materials are stainless steel and titanium. In its standard finish, stainless steel has a more polished surface than titanium, leading to different surface microtopography, which has effects on tissue integration and bacterial adhesion., The smooth surface of stainless steel tends to lead to fibrous encapsulation but lower bacterial adhesion. The rougher surface of titanium tends to result in osseointegration with bone or direct soft tissue integration, and relatively higher bacterial adhesion. These findings have been shown for test surfaces in a laboratory setting and fracture fixation plates, nails, and screws in animal studies. How these differences may influence pin tract infection remains to be convincingly determined.
Furthermore, pin coatings loaded with active antimicrobial agents have been proposed, some of which have been applied within hydroxyapatite (HA) coatings, or directly on the surface of the metal., The application of such coatings in the clinic is more advanced for prostheses rather than external fixation pins at the present time. The most commonly used coating on external fixation pins is HA, which has the advantage of improved osteointegration and, therefore, potential to prevent pin loosening., Some authors state that pin loosening may lead to an increasing number of pin-tract infections, and therefore the HA coating could reduce the incidence of pin tract infection, however, many also consider loosening and infection as two different processes.,, The benefit of HA coating on pin site infection, therefore, may require further studies to fully understand the clinical benefits.
Active coatings, incorporating active antibacterial agents such as silver, or antibiotics, have also been analyzed in a range of in vitro and in vivo studies.,,,,, In contrast to the HA-coated pins, which have no direct antibacterial activity, antimicrobial coatings aim to prevent bacterial survival at the surface. Such coatings should of course prevent infection, but crucially, should not prevent osteointegration, which can lead to the development of pin loosening. The most commonly studied coatings include, HA loaded with antimicrobials, or silver functionalized surfaces.
Despite the quite significant basic research into implants: tissue interfaces and materials optimization, the translation of this knowledge to clinically available external fixation pins has been limited. Furthermore, it is unclear if the laboratory data showing different interactions between tissue, bacteria, and implant surfaces translate to clinical reality. The aim of this systematic review and meta-analysis was to analyze the current evidence of the effect of pin material and pin coating on the incidence of infection in external fixator pin sites.
| Methods|| |
A systematic review was undertaken using all levels of evidence and following Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines and registered with Prospero (ID CRD42021273881). PubMed, Embase, and Cochrane reviews were searched for relevant studies. An initial search was performed to determine relevant search terms for the primary outcome. The search term used was ([external fixat*] OR [Ilizarov] OR [taylor spatial frame] OR [schanz]) AND ([infection] OR [osseointegration] OR [osteomyelitis]) AND ([titanium] OR [HA] OR [silver] OR [nanosilver] OR [antibiotic coat*] OR [stainless steel] OR [cobalt chromium] OR [iodine] OR [coat*]).
The search was performed on August 31, 2021, and resulted in 265 studies, for which the titles were reviewed. Following this, 47 abstracts were reviewed and subsequently 19 papers were viewed in full by two authors independently (SA and TJ). Eight papers were included in the final analysis.
The inclusion criteria for the studies were (1) recorded diagnosis of infection based on the authors definition, (2) external fixator for any cause, (3) any bone, (4) English language, (5) human patient study, and (6) known pin material. The exclusion criteria were (1) in vitro studies and (2) no clear classification or definition for pin site infection. All studies included an intervention where patients underwent an external fixation for any indication. The indications for surgery included fracture management, limb realignment surgery, and limb lengthening surgeries. The outcome was calculated on the incidence of pin site infection defined based on the Checketts classification, Schmidt et al. classification, or the published authors' own definition of pin site infection.,
Two reviewers independently reviewed all papers at all stages of the review process. Paper selection was performed using Raayan (Rayyan. Rayyan system inc. Version 2016). The data were extracted and recorded on Microsoft Excel. The recorded data included the number of pins and patients in each group and number of infections. If there was any disagreement between the two reviewers, and an agreement could not be found, the senior author had the final decision. No further studies were identified when examining the bibliography of all reviewed papers.
Statistical analysis was undertaken using StataCorp. 2017. Stata Statistical Software: Release 15. College Station, TX: StataCorp LLC. Basic percentages of infection rates were calculated. Following this, a random effects model meta-analysis was performed. Odds ratios with 95% confidence intervals (CIs) were produced.
Study bias was assessed using the Cochrane risk of bias tool Rob II. Strength of evidence was based on the American Academy of Orthopaedic Surgeons methodology for Defining the strength of recommendation [Table 1]. This divides the evidence into strong, moderate, low, and consensus based on the number and quality of studies.
|Table 1: Adapted methodology from the American Academy of Orthopedic Surgeons for defining the strength of the recommendation and evaluating it|
Click here to view
| Results|| |
Following literature review, and screening by two separate reviewers (SA and TJ), only 8 papers were included in the final analysis [Figure 1].
|Figure 1: PRISMA flow diagram. PRISM: Preferred Reporting Items for Systematic Reviews and Meta-Analysis|
Click here to view
The study characteristics and patient demographics are included in [Table 2], also showing surgery indication, pin material, and the classification system used to report infection.
Pin material: Stainless steel versus titanium
Pieske et al. in 2008 performed an randomized controlled trial (RCT) in wrist external fixators. They randomized 80 patients into either titanium or stainless steel pins. Two patients in the stainless steel group had external fixator pins removed prior to healing due to infection compared with 0 in the titanium group. Three patients in the stainless steel group required oral antibiotics and 2 in the titanium group. The odds ratio was 1.00 (95% CI: −0.70–2.70), [Figure 2].
Overall strength of evidence: Limited
Limited (Low strength evidence or conflicting evidence).
Pin coating: Stainless steel versus hydroxyapatite
Three studies,, compared stainless steel and HA pins with a cumulative odds ratio of 0.25 (95% CI: −0.52–1.02) demonstrating no significant difference in the incidence of pin site infection [Figure 3].
Pieske et al. analyzed a total of 40 patients with wrist external fixators for fractures. They diagnosed infection as the presence of erythema, drainage, or pain. They found 2 infections in the HA group (10.5%) and 3 infections in the SS group (15.8%) which involved 4 pins (P = 0.631). Placzek et al. analyzed 47 HA-coated pins in 12 monolateral external fixators and 45 stainless steel pins in 9 monolateral external fixators for limb lengthening. Infection was diagnosed by the classification of Schmidt et al. Five of the 47 HA screws (11%) and 4 of the 45 steel screws (9%) had a grade 3 or 4 infection, which are infections with secretions with or without loosening. Pizà et al. undertook a RCT in 23 patients undergoing limb lengthening comparing HA and uncoated pins. Diagnosis of infection was by the Checketts and Otterburn criteria for pin site infection. They found 97 (60.2%) in HA-coated and 102 (63.4%) in stainless steel pins. The incidence of major infections classified as a Checketts and Otterburn classification of 4–6 was 6 (3.7%) in the HA pins and 9 (5.6%) in stainless steel pins with no significant differences between the two groups.
Overall strength of evidence: Limited
Limited (Low strength evidence or conflicting evidence).
Pin coating: Titanium versus hydroxyapatite
Two studies, analyzed titanium compared to HA-coated pins with a cumulative odds ratio of 1.12 (95% CI: −4.25–6.48), demonstrating no significant differences in incidence of pin site infection [Figure 4].
Pieske et al. in 2011 undertook a RCT that compared 20 patients in each group undergoing wrist external fixation for trauma. They diagnosed infection by erythema, drainage, and pain. They found infection in 2 with HA coatings and 0 with stainless steel. Of these 2 infections, 1 was superficial and 1 was deep infection, but the differences were not significant. Pommer et al. in 2002 undertook an RCT with 46 patients for a variety of indications including lengthening, fractures, infection, and tumor. A total of 165 pins were coated with HA and 169 were made of titanium. Twenty (11.8%) of titanium pins developed infection, while no HA pins did (P < 0.001).
Overall strength of evidence: Limited
Limited (Low strength evidence or conflicting evidence).
Active antimicrobial pin coating: Silver coated versus stainless steel
Two studies, analyzed silver compared to stainless steel with an odds ratio of 0.12 (95% CI: −0.89–1.12), demonstrating no significant differences in incidence of pin site infection [Figure 5].
Coester et al. undertook an RCT in 19 patients undergoing tibia fracture fixation. They used their own 4-grade classification of pin site infection. They found 10 superficial infections in the silver and 7 in the stainless steel. They concluded that there was no difference in the performance of either pin. Masse also undertook an RCT in fracture fixation in 24 patients with 50 silver coated pins and 56 stainless steel pins. Infections were found in 30% of silver-coated pins and in 42.9% of SS pins from pin tip cultures following removal of the pin. They noted no difference in clinical behavior between the two pins. The study was stopped early due to the detection of a significant increase in the silver serum level.
Overall strength of evidence: Limited
Limited (Low strength evidence or conflicting evidence).
Risk of bias
Risk of bias was assessed in all the studies. Overall, 0 studies had a low risk of bias, 4 studies had an unknown risk of bias, and 4 studies had a high risk of bias [Table 3].
| Discussion|| |
Pin site infection is a common complication associated with the use of external fixation that may resolve relatively easily with pin site care and oral antibiotics or progress to deep bone infection requiring extensive intervention. The risk of developing a pin site infection, and the clinical course that follows, is believed to be influenced by a number of factors; however, little in the way of clinical evidence on the role of pin material and coatings is available. This systematic review analyzed the effect of pin material and pin coatings on the incidence of pin site infections associated with external fixators.
When comparing bare, uncoated metal pins, titanium and steel are the two metals most commonly used for external fixation pins. Titanium has been shown to demonstrate favorable mechanical properties for external fixators and is resistant to corrosion due to the spontaneous oxide layer that forms on its surface, which also supports its biocompatibility. Previous studies into fracture fixation devices suggested improved performance of titanium over steel with regard to infection risk., This has not been a universal finding and more recent systematic reviews could not show any consistent effect for osteosynthesis devices. Our systematic review identified only one suitable clinical study comparing bare, uncoated pins of steel and titanium. In a prospective study, Pieske identified a slight benefit of titanium pins for distal radius fractures that did not reach clinical significance. Considering the lack of significant data, further studies would be required to provide definitive guidance.
The larger proportion of included studies investigated coated versus uncoated pins. The most commonly used coating for external fixation pins is HA, which is used due to its osteoconductive properties, and it has been shown to result in less pin track loosening and increased extraction torques. Contrasting results were found across the studies comparing HA to uncoated titanium pins. Pommer et al. found significantly less infections with HA, while Pieske found more infections with HA., Similarly, when comparing stainless steel with HA-coated pins, there was no difference in the incidence of infection.,, Therefore, similar to previous reviews, the effect of HA-coated pins on infection and malunion is not clear, and further high-powered studies are required. It may be that HA coating has a greater impact than the selection of titanium or steel; however, until further data becomes available, the issue remains controversial.
The use of antimicrobial coatings may offer greater protection against bacterial infection, but the benefits must be proven considering the appropriate concern over excessive use of antimicrobials, and the concerns that such active agents, or the coatings in which they are loaded, impacting tissue integration. A range of coatings including antibiotics, nanosilver, silver, and chitosan have been tested. Silver for instance has known antimicrobial properties, and may be particularly suitable for external fixation pins due to its broad-spectrum activity and lack of any significant resistance development. While many of these have shown initial promising results in the laboratory, there have been limited clinical studies, aside from silver-coated pins. Of the two included studies in this review, there was, however, no difference between silver-coated pins and stainless steel pins., The relatively low number of patients suggests that further studies are required. Considering the importance of tissue integration to the health of the pin site, any antimicrobial surface should also be closely followed for tissue integration in addition to pin site infection. Of course, the increased use of antimicrobial agents in medical devices can raise concerns over antimicrobial resistance (AMR). Increasingly, bacterial pathogens of clinical concern are resistant to key antibiotics or other antimicrobials. The indiscriminate use of antibiotics can contribute to the further spread of AMR. Therefore, the use of antibacterial surfaces on these devices should be carefully considered in order to avoid increased prevalence of multidrug-resistant pathogens in the hospital environment.
A major issue with any study in pin site infection, or indeed any other aspect of pin site health, is the methodology to diagnose pin site infection, which we found to vary between the studies. The diagnosis used in the included studies was based on several classifications such as the Checketts classification and the Schmidt classification., Pommer et al. diagnosed infection based on bacterial culture of the pin following removal, which may not reflect active infection even if the pin site is contaminated. Further studies to analyze pin site infection need to have clear criteria for the diagnosis of infection to ensure reproducibility and prevent potential bias. A standardized classification that determines superficial and deep infection of pin sites should also be applied to all studies.
A number of limitations should also be considered for the data that is presented here. Considering the fact that infection of a pin site may be associated with duration of pin placement, this would be an important factor to evaluate. Unfortunately, it was impossible to draw conclusions on duration of external fixation and infection in this review as this was not reported in several studies. Indeed, there is a significant gap in our knowledge of the basic pathophysiology that occurs surrounding an external fixation pin, with regard to epithelialization, bacterial colonization, and the incidence of pin loosening versus infection. An additional limitation is the fact that this review did not analyze the incidence of pin site loosening and extraction torque. Several studies have reported a higher extraction torque in HA coated pins and reduced loosening which in theory could lead to lower rates of pin site infection., However, these parameters are often not available in the available literature.
In terms of the overall findings, an additional limitation is the low number of studies included. Despite the widespread use of external fixators, there were very few studies that could be included. Three of the included studies were all from one author, with some overlap of populations. Most of these studies had small numbers and were of low overall quality with a high risk of bias using the Rob II risk of bias assessment. There were no large studies that were adequately powered to determine a difference in the incidence of infection. The majority of studies were over 10 years old with no recent studies included. A further limitation is the varied indications for the use of external fixators. It is a concern that different indications for external fixators may have different rates of pin site infection and combining these into a single study or a meta-analysis may not be appropriate.
| Conclusion|| |
This systematic review and meta-analysis are the most up to date analysis on the role of pin site materials and coatings on the incidence of pin site infection. There is currently limited evidence to base recommendations and further studies are required to identify all of the aspects investigated in this study: stainless steel versus titanium; HA coated versus uncoated; and antimicrobial coated versus uncoated. Ideally, these future studies should be randomized trials where there is a single indication for the external fixator, and the Checketts and Otterburn classification used to determine pin site infection rates, and the duration of pin placement before infection is recorded.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
[Table 1], [Table 2], [Table 3]