|Year : 2022 | Volume
| Issue : 3 | Page : 24-30
Effect of frame and fixation factors on the incidence of pin site infections in circular external fixation of the tibia: A systematic review of comparative studies
Maritz Laubscher1, Luan Nieuwoudt2, Leonard Charles Marais2
1 Orthopaedic Research Unit, Division of Orthopaedic Surgery, Groote Schuur Hospital, University of Cape Town, Cape Town, South Africa
2 Department of Orthopaedic Surgery, School of Clinical Medicine, University of KwaZulu-Natal, Durban, South Africa
|Date of Submission||17-Jan-2022|
|Date of Decision||13-May-2022|
|Date of Acceptance||22-Jul-2022|
|Date of Web Publication||12-Oct-2022|
Orthopaedic Research Unit, Division of Orthopaedic Surgery, Groote Schuur Hospital, University of Cape Town, Cape Town 7925
Source of Support: None, Conflict of Interest: None
Introduction: Pin site infections (PSIs) are frequent complications encountered with the use of circular external fixators. PSIs range in severity, and the numerous factors have been suggested to affect the incidence. We aim to perform a systematic review of all comparative studies including circular external fixation applied to the tibia diaphysis in adult patients and to explore frame and fixation factors that may be associated with the development of PSI. Materials and Methods: We conduct a systematic review of the literature according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines to assess the available data with the specific focus on frame factors that might contribute to the development of PSI. A literature search of major electronic databases was conducted to identify journal articles. A scoping review process was adopted due to the expected broad variation of studies in our research topic using the PRISMA for Scoping Reviews guidelines. Results: The initial electronic database search produced 360 publications. After a review process, only four publications were retained for final analysis. Type of fixation pins and wires, frame fixation configurations, and reconstructive methods were compared in these studies. There are very few clinical studies comparing the different frame and fixation factors that can influence PSI rates in circular external fixation. The available studies reflect a significant degree of bias and confounding, representing a low level of evidence. Conclusion: Further research is needed, and with the present paucity of data, it is not possible to make any firm recommendations. Within the same frame construct, it appears that tensioned wires may carry a lower risk of PSI than half-pins.
Keywords: Circular external fixators, frame factors, pin site infections, tibia
|How to cite this article:|
Laubscher M, Nieuwoudt L, Marais LC. Effect of frame and fixation factors on the incidence of pin site infections in circular external fixation of the tibia: A systematic review of comparative studies. J Limb Lengthen Reconstr 2022;8, Suppl S1:24-30
|How to cite this URL:|
Laubscher M, Nieuwoudt L, Marais LC. Effect of frame and fixation factors on the incidence of pin site infections in circular external fixation of the tibia: A systematic review of comparative studies. J Limb Lengthen Reconstr [serial online] 2022 [cited 2022 Dec 1];8, Suppl S1:24-30. Available from: https://www.jlimblengthrecon.org/text.asp?2022/8/3/24/358256
| Introduction|| |
Circular external fixators are frequently used to treat complex skeletal trauma.,,, They are also widely used, particularly on the tibia, in limb reconstruction procedures, such as deformity correction, limb lengthening, and treatments of nonunion and bone infections.,,, These procedures are associated with relatively high complication rates due to the complexity of the pathology being addressed, the procedures' inherent technical intricacy, and the extended periods that the frames need to be kept in situ., Of all the complications associated with these procedures, pin site infection (PSI) is possibly the most frequent.,,,, Severity may vary, and resultantly, a number of descriptive classification systems have been developed in an attempt to categorize PSI.,,
Numerous factors have been suggested to affect the incidence of PSI. These include host factors, the type of pin or wires used, insertion techniques, and the management of the pin site after application of the frame. Another major factor that may influence the risk of PSI is the external fixation frame construct itself. There are several aspects relating to frame design and construction that might be relevant. Circular fixation encompasses a variety of constructs, including traditional Ilizarov-type fixators, six-strut hexapod-type fixators, and so-called trauma fixators utilizing special struts that allow for easy adjustment. Each type of fixator is also modular, enabling a wide array of configurations. This adaptability facilitates its use when dealing with complex pathologies, but different designs may also impart a change in the risk of PSI. In addition, there is an assortment of methods by which the frame can be fixed to the bone, including different types of wires and pins, as well as an array of connected devices that fixate the frame pins. It is controversial whether the different clamps or fixation bolts alter the rate at which wire tension is lost. It remains unclear exactly how the type, number, orientation, and fixation of different wires and pins affect the rate of PSI. Furthermore, pin loosening can be the cause or the result of PSI. Construct instability may also contribute to an increase in the PSI rate.,, Excessive translation of the circular frame, within the soft tissue envelope, leads to unacceptably high motion at the pin–skin interface, which is thought to contribute to PSI., This excessive movement may not only increase the PSI rate but also affect biomechanics at the fracture site and could lead to the development of fracture-related infection and/or nonunion.
We aimed to perform a systematic review of all comparative studies including cases where circular external fixation was applied to the tibia diaphysis in adult patients and that reported PSI as an outcome measure. We explore aspects related to the indication for use, frame design and construct, and fixation methods that may be associated with the development of PSI.
| Methods|| |
We conducted a systematic review of the literature according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines to assess the available data with a specific focus on frame factors that might contribute to the development of PSI. The risk of PSI varies per anatomic location, and the tibia was chosen as it is the most common site of circular external fixation. There are several studies involving circular fixation that reported the PSI rate. However, due to the heterogeneity of indication, constructs, fixation, application methods, and postoperative care protocols, it is not possible to make any conclusions about the impact-specific factors that may have had on the PSI rate without a control group. For this reason, only comparative studies were included.
A scoping review process was adopted due to the expected broad variation of studies in our research topic using the PRISMA for Scoping reviews guidelines of 2018., The review included the following steps: (1). identifying the research question; (2) earmarking relevant studies; (3) selecting the studies; (4) charting, collating, and condensing the data; and (5) reporting our results. Due to the brevity of data on the topic, a quantitative component was not possible.
Peer-reviewed comparative studies reporting PSI as an outcome measure were considered eligible, with the following requisites for inclusion: original peer-reviewed prospective or retrospective comparative studies including randomized control trials, nonrandomized controlled trials, quasi-experimental, and case–control studies, analytical or cross-sectional studies (evidence level 1–4), involving circular external fixation applied to the tibia of adult human subjects (older than 13 years of age), published at any time and in English.
The following studies were excluded: basic science (nonclinical) studies, noncomparative studies, case series or case reports with <10 patients, narrative or systematic reviews, congress proceedings, letters to editor, and editorials. Studies were also excluded from the analysis if there were insufficient data available to be extracted from an original article, involved monolateral, rail and hybrid external fixators, or if the comparison was between external fixation-only and external plus internal fixation.
The search was performed on July 22, 2021, on Scopus, Web of Science, and PubMed databases. The search was conducted using a combination of free text, and Medical Subject Headings (MeSH terms as per 2021 MeSH Descriptor Data) used were: ((pin site infection) OR (pin track infection) OR (pin tract infection) OR (pin site sepsis) OR (pin track sepsis) OR (pin tract sepsis)) AND ((Ilizarov) OR (Ilizarov technique) OR (circular frame) OR (Ilizarov frame) OR (circular external fixator) OR (hexapod) OR (hexapod fixator) OR (fine-wire) OR (Taylor Spatial Frame)) AND ((tibia) OR (tibial) OR (tibia fracture)). Limitations we applied included English language studies as well as human studies [Figure 1].
Eligible search citations were initially exported to EndNote (EndNote X9.3.3, Clarivate, Philadelpha, PA, USA), deduplicated, and then uploaded to Rayyan® Intelligent Systematic Review software (web version, http://rayyan.qcri.org), for an independent blinded title and abstract study screening process by authors LM and LN. Each study was scrutinized on two broad categories: a comparison of different frame constructs or fixation options followed by the assessment of reporting and/or classification of the outcome of interest, being PSI rates per group. There was full agreement on the studies selected for inclusion after discussion by the study selection authors.
Due to the explorative nature of this systematic review, as well as the nature of the outcome of interest data, only a brief qualitative description was reported on each of the included studies. An author (ML) then extracted data from the four included studies. The specific study design, sample size, location, frame indication, frame design, as well as the outcome and complications of the management strategy employed for each identified article were reviewed. A qualitative description was reported as per the PRISMA guidelines.
| Results|| |
The initial electronic database search produced 360 publications. Initial screening by titles and abstracts identified 11 potentially eligible studies.,,,,,,,,,, Full-text review of these 11 studies resulted in four publications being retained for final analysis [Figure 1].
Three publications were retrospective cohorts or case–control studies and one a prospective observational study. Publications were assigned a level of evidence according to Sackett's Rule of Evidence which ranks studies according to the probability of bias. All three retrospective studies were assigned as level 4 evidence and the prospective study as level 3. Study sample size ranged between 20 and 100, with a total of 220 cases.
Type of fixation pins and wires
Green et al. reported on the difference in PSI with different materials used. They compared tensioned stainless steel wires with titanium half-pins mounted to an Ilizarov circular external fixator. Ten frames were applied to either femur (one infected nonunion and one bone defect), tibia (four nonunions, two malunions), or both the femur and tibia (two cases) using half-pins only. In the other group, ten tibia frames were applied using only tensioned wires (eight nonunions, one growth arrest, and one leg-length discrepancy). The authors reported 15 minor and four major PSIs in the titanium half-pin group versus 24 minor and 10 major infections in the stainless steel-tensioned wire group. It was concluded that significantly more PSIs occurred in the stainless steel wire group. Their series also reported more broken half-pins than wires. PSIs were not reported according to the region (femur or tibia).
Makhdoom et al. performed an observational, prospective single-center study comparing PSI rates between tensioned wires and half-pins. 100 cases of circular frames for distraction osteogenesis were prospectively followed up with 170 half-pins and 720 wires evaluated using the Paley Grading System. The study included frames applied to the tibia, femur, humerus, and forearm. The incidence of PSI with tensioned wires was 46 (53.5%) grade 1, 25 (29.1%) grade 2 and 15 (17.4%) grade 3. In the case of the half pins' PSI rates, the majority were grade 2 (22 of 40, 55%), followed by grade 1 (12 of 40, 30%) and grade 3 (6 of 40, 15%). Of note is that all patients routinely received 8 days of postoperative antibiotic therapy after application of their Ilizarov frame (initial 3 days of intravenous antibiotics, followed by 5 days of oral antibiotics). The overall incidence of PSI in their series was 17%, and they conversely found significantly more infected half-pins (40 of 170, 24%) compared to wires (86 of 720, 12%).
Frame fixation configuration
Baruah compared conventional all-wire fixation Ilizarov frames versus a hybrid assembly using tensioned wires and half-pins combinations. This retrospective analysis involved 25 cases of infected nonunions of the tibia in each group. No difference in union rate or functional outcome was observed. PSIs were compared in the two groups and reported using the Paley Classification System. There was only one grade 3 PSI in the hybrid group and none in the all-wire group, with no significant difference between the two groups. It was not reported whether the single grade 3 PSI was at a wire or pin site.
Green et al. reported lower overall and fewer major PSI rates using half-pin–only Ilizarov frames versus all-wire frames. The half-pin–only group also had shorter overall time in frames, decreased pain scores, improved weight-bearing, as well as better range of motion in the adjacent joints compared to the fine-wire–only group.
Wu et al. compared the outcomes of bone transport with bone shortening–lengthening procedures using the Ilizarov technique. They included 28 bone transport and 22 shortening–lengthening cases in their retrospective cohort. The authors concluded similar outcomes, although shortening–lengthening procedures had a shorter time to union and overall higher union rates. They reported that PSI and pin loosening occurred in 54% (12 of 28) in the bone transport group, compared to 41% (9 of 22) in the acute shortening–lengthening group. The difference was not significant and the bone transport group had longer frame durations as it was used to treat larger defects.
| Discussion|| |
The use of circular external fixators is a well-established treatment method with a wide variety of indications. PSI is by far the most frequent complication encountered and is often regarded as an almost inevitable complication. Despite this, there is a general lack of consensus about how it can be prevented. There are numerous obstacles that limit our ability to develop evidence-based guidelines for the prevention of PSI, including lack of uniform definitions and classifications, variability in implants and techniques being used, as well as the lack of consistency in terms of the outcome in terms of PSI per pin/wire or per patient. The scoring systems or classifications used to describe PSI are descriptive and not all validated.,, With this systematic review, we have identified a lack of clinical comparative studies. In addition, there are often numerous differences between the compared groups such as underlying pathologies or fixator constructs which may represent significant confounding factors. Even the studies we included all represent low levels of evidence. We planned to limit our search to frames applied to the tibia, yet two of the studies included frames applied to other regions. PSI was not reported per region in these papers introducing significant bias., Makhdoom et al. also excluded patients with common conditions such as diabetes, smoking, and renal failure, which may influence the risk of PSI and therefore may not reflect routine practice.
PSIs can range from minor to more severe infections requiring unplanned reoperations and potential permanent disability. Even minor infections can cause significant patient discomfort and hinder active rehabilitation, which is an integral part of the treatment strategy with circular external fixators. The reported incidence of PSI ranges from 10% to 100%. There are likely many factors contributing to the development of PSI, including host factors, duration of treatment, limb segment involved, insertion technique, pin site care protocol used, as well as frame factors., While a number of interventions have been proposed to reduce the risk of PSI, there is limited clinical evidence, particularly in terms of implant-related factors such as materials and coatings.
It is conceivable that a number of frame-related factors may be associated with PSI. The type of materials used (different metal compounds), the fixation method (tensioned fine-wires vs. half-pins versus a combination of wires and pins), frame configuration (hybrid vs. a traditional Ilizarov-type frame), and specific indication for frame application might all influence the development of PSIs. Any instability in the frame construct may further contribute to the development of PSI. Frame instability leads to increased movement at the pin–bone interface, producing pin site irritation and infection. Ring fixators have been shown to have a lower incidence of PSI compared to monolateral or hybrid fixators, all of which is thought to be related to the overall improved stability of ring fixators.
Clinical practice suggests that frame factors may contribute to the development of PSI. There is however little data to elucidate this, and it remains unclear which factors are clinically relevant and can be modified to mitigate against infection. In addition, because the development of PSI is multifactorial, it is difficult to evaluate the specific contribution of each individual aspect to the development of PSI. PSI is not consistently reported with the variety of classification systems available. Even the description of the incidence is not consistent in the literature with PSI described as either per case or sometimes per wire.
The material from which pins or wires are manufactured is also thought to possibly play a role. While stainless steel is less elastic and has a higher yield strength, it is been suggested that titanium implants may impart a reduced risk of infection. However, this benefit remains unsubstantiated in clinical practice, and the animal studies suggests that there may in fact be no difference in infection risk. Our systematic review revealed no clinical studies directly comparing the risk of PSI between similar pins or wire made from stainless steel and titanium. Green et al. concluded that there was a lower incidence of PSI with titanium pins compared to stainless steel implants. They did however compare titanium half-pins to stainless steel-tensioned wires, and the difference in PSI rates might have been related to the difference in pin design or tension. It is also possible that the site of insertion may have played a role as pins or wires in cancellous bone might have a different infection rate from pins located more centrally in diaphysis.
There are numerous surface coatings that may decrease the risk of PSI. However, we were unable to identify controlled clinical studies looking at this specifically in circular external fixation. Hydroxyapatite (HA)-coated pins have been associated with improved fixation stability and significantly lower rates of osteolysis compared to noncoated pins. Comparative studies have however been performed using mainly monolateral fixators. Pommer et al. compared two groups consisting of 23 patients each undergoing bone lengthening or transport with monolateral external fixators. They noted no pin loosening or infection in the HA-coated stainless steel group, compared with 20 infections and 22 loosened pins in the noncoated titanium pin group. Pizà et al. also found decreased pin loosening but similar PSI rates with noncoated and HA-coated stainless steel half-pins used with monolateral external fixators for limb lengthening. Moroni et al. performed a prospective randomized study comparing HA-coated and uncoated stainless steel pins in 38 patients' femur or tibia. Most cases again involved monolateral fixators, with only seven circular frames. The PSI rate was noted to be significantly lower in the HA-coated group.
Initially, the Ilizarov circular fixators employed tensioned transosseous wires as the sole means of osseous fixation. To achieve adequate wire crossing angles for stability, muscle impalement is unfortunately mostly unavoidable. Half-pins were introduced to improve implant tolerance and muscle function. By adding half-pins to an all fine-wire fixator (in the appropriate configuration), the construct rigidity is increased and relative motion between the bone fragments reduced. While this may confer a potential advantage in terms of stability, it also changes the mechanical environment at the bone–fragment interface which may affect union. The aim, ultimately, is to create a balance with the optimal mechanobiology at the fracture site while reducing complications such as PSI. It is suggested that half-pin–only configurations are deemed “stable enough” for clinical use and may possibly reduce the rate of PSI. There are contradictory reports in the literature on PSI rates of tensioned wires versus half-pins. Some studies report no difference when comparing tensioned wires to half pins. Others report lower PSI rates with half-pins. The study by Makhdoom et al. reported a significantly lower incidence of PSI with tensioned wires compared to half-pins when using comparable frame constructs, although one needs to acknowledge the potential effect of different body locations on PSI incidence in this study.
When comparing different frame configurations, Baruah reported a similar PSI incidence with all-wire fixation Ilizarov frames versus hybrid assembly frames when using tensioned wires and half pins (although the exact numeric result is not reported). Green et al. found fewer PSIs in all half-pin frames. No studies included in our series compared PSI with Ilizarov circular fixators versus hexapod fixators. We also found no studies reporting PSI rates between different frame manufacturers.
There is no clear evidence that the indication for treatment influences the rate of PSI. Wu et al. reported higher incidence of PSI with bone transport frames compared to shortening–lengthening cases. They also found significantly longer overall treatment duration in their bone transport group. Previous studies have shown that the risk of PSI increases with the duration of external fixation. Increased time in frame may also play a role in the increased incidence in PSI with bone transport procedures.
The recommendations from this review are limited by the paucity of data and low level of evidence in the included studies. A degree of bias inherent in the design of several of the papers included made extrapolation of their findings very difficult. All the included papers have significant limitations when trying to identify frame and fixation factors affecting PSI. It is therefore not possible to draw any meaningful conclusions due to the lack of reliable data. The heterogeneity and quality of the included studies precluded performing a quantitative analysis. While we limited our search to circular external fixation of the tibia in an attempt to decrease the number of confounders, this also limited the number of eligible studies. This however revealed a significant gap in the literature. We encourage orthopedic trauma and reconstructive surgeons to evaluate the incidence of PSI and investigate which frame and fixation factors can influence this. Although PSI is common, only a very few lead to major complications. It might therefore be more useful to only evaluate the incidence of significant PSI when comparing different factors. There is a need for well-designed prospective studies to inform future guidelines and recommendations. It is also difficult to separate the effect on PSI incidence of frame and fixation factors from pin site care. PSI should be investigated in a systematic way, starting with developing validated tools to measure PSI. Pin site care techniques should be standardized, participants randomized, participants and pin site numbers recorded, similar pathologies compared, and frames should be applied to the same region.
| Conclusion|| |
There are very few clinical studies comparing the different frame and fixation factors that can influence PSI rates in circular external fixation. The available studies reflect a significant degree of bias and confounding, representing a low level of evidence. Further research is needed, and with the present paucity of data, it is not possible to make any firm recommendations. Within the same frame construct, it appears that tensioned wires may carry a lower risk of PSI than half-pins. Adding half-pins to an all-wire frame may increase stability, but the effect of this on PSI rate also remains unclear.
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Conflicts of interest
There are no conflicts of interest.
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