This nation-wide cohort study showed that the rate of SSI after DRF surgery was highest among patients undergoing external fixation (28%), followed by percutaneous pinning (12%) and plate fixation (5%). In addition, the classification tree analysis showed that surgical method, fracture type (closed/open), sex and age were factors associated with the prescription of antibiotics (Flucloxacillin and/or Clindamycin). The highest proportion of antibiotics prescription was found among patients undergoing external fixation of an open fracture (58%), followed by externally fixated closed DRFs in men aged ≥75 years (53%).
SSI rates – relation to previous research
The existing literature on DRF treatment and outcome is extensive and heterogenic. Several previous prospective randomized controlled trials (RCT) comparing the main surgical methods in the treatment of displaced DRFs with regard to patient-reported and functional outcomes have also presented data on the occurrence of SSIs. The reported SSI rates varied between 0 and 5.6% after plate fixation [8, 10,11,12, 17, 30], between 7.8 and 23% after percutaneous pinning [10, 11, 17], and between 5.3 and 26% after external fixation [8, 12, 17, 30]. The great variance in SSI rates for each surgical method between these studies may be explained by differences in inclusion and exclusion criteria (e.g. patient age, fracture classification and type), size of the study population, as well as the definition of SSI. Furthermore, these studies were designed to detect differences in clinical outcome, and SSI rates were presented only as secondary outcomes. Interestingly, it was the largest of these previous studies, a secondary analysis of 461 patients included in a multicenter pragmatic RCT and allocated to either volar plate fixation or percutaneous pinning, which reported SSI rates most in accordance with those in our study; 5.6% for plate fixation and 8.3% for percutaneous pinning .
A recent Cochrane systematic review of percutaneous pinning in the treatment of DRFs in adults , pooled data from 21 RCTs and 5 quasi-RCTs comparing either pinning with cast immobilization, different pinning techniques, or immobilization regimes for displaced or unstable DRFs in a total of 1946 patients, with regard to short-, medium- and long-termpatient-reported outcomes and complications. They reported an SSI rate of 7.7% (ranging from 0 to 15%) in the 285 patients treated with percutaneous pinning.
A meta-analysis comparing treatment outcomes and complication rates between volar plate fixation and percutaneous pinning in the treatment of dorsally displaced DRFs pooled data from seven RCTs with a total of 875 patients, and reported a rate of superficial SSI of 3.2% after volar plate fixation and 8.2% after percutaneous pinning, while the rate of deep SSI was 0.5% for both methods .
Another meta-analysis compared volar plate fixation to external fixation in the treatment of DRFs in adults by pooling data from nine RCTs with a total of 780 patients , and reported SSI rates of 0.5% after plating and 7.7% after external fixation. This was markedly below our findings of 5% and 28% respectively.
In contrast to our findings, a literature review from 2015 on the management of complications following DRF treatment reported a higher SSI rate after percutaneous pinning (33%) than after external fixation (21%) . However, these numbers were based on two previously published studies, one of which prospectively compared the rates of pin tract infection between buried and percutaneous wires in 56 patients , and the other which retrospectively analyzed complications in 314 DRF patients treated with external fixation .
A previous retrospective study by van Leeuwen et al. analyzed the occurrence of pin site infection and associated factors in 1213 patients undergoing percutaneous pinning of fractures in the wrist and/or hand at one of three institutions, by reviewing medical charts . They defined SSI either by early removal of pins, prescription of antibiotics for pin problems within 90 days, or surgery for infection related to the pin. The reported SSI rate was 7%, and a majority of infections were superficial and resolved with peroral antibiotics and/or pin removal.
Associated factors – relation to previous research and further considerations
In our study, age was associated with prescription of antibiotics for patients treated with both percutaneous pinning and external fixation, with a higher proportion of antibiotic prescription among patients ≥75 years. In the previously mentioned study of factors associated with pin site infection by van Leeuwen et al. , high age was associated with infection in their bivariate analysis, however in their multivariable analysis, no individual factor (including age, smoking, fracture location, fracture mechanism or number of pins) was associated with increased or decreased odds for pin site infection. Furthermore, we found no association between age and antibiotic prescription for patients treated with plate fixation. This is supported by a recent retrospective study of age-related outcomes and complications in 105 patients (aged 17–80 years) treated with volar plate fixation , in which no significant difference in overall complication rate between patients aged younger or older than 55 years was found, and the rate of SSI was 3.4% for younger patients and 4.3% for older.
Our findings of an association between antibiotics prescription and fracture type (closed/open), with a higher proportion of antibiotics prescription among patients with an open fracture, were not surprising and in accordance with current knowledge and our clinical experience. They are explained by a well-established inherently increased risk of SSI due to contamination of the surgical site . However, as open fractures may vary considerably in severity, we cannot exclude that some of these prescriptions were prophylactic.
Our study showed an association between male sex and prescription of antibiotics as indicated by an aOR of 2.0 in the multivariable logistic regression model, as well as a higher proportion of antibiotics prescription among men compared to women regardless of surgical method and node level in the classification tree analysis. To the best of our knowledge, SSI rates in relation to gender have not previously been studied. We speculate that our findings may be due to a higher percentage of high energetic trauma among men and thus an inherent higher risk of infection. Another possible explanation may be a tendency among health-care providers to treat men with prescribed antibiotics to a greater extent than women. Further studies are needed to investigate this.
Aspects of study design and methods, strengths and limitations
The great number of included patients in this study warranted high precision. Further, the high coverage of the population-based registers (the NPR and the SPDR) reduced the risk of selection bias.
We chose to investigate SSI after DRF surgery by the use of a proxy because the coding of SSI after fracture fixation in the NPR was not considered consistent or reliable, most likely due to the previously reported lack of consensus on definition and classification in clinical practice . Given the strongly regulated and well-monitored pharmaceutical system in Sweden , as well as the extensive multi-levelcross-sectoral national efforts to contain antibiotic resistance over the recent decades, in which the Swedish strategic program against antibiotic resistance (STRAMA) has played a central role , providing guidelines for antibiotic use, we believe that the use of a dispensed prescription of peroral Flucloxacillin and/or Clindamycin as a proxy was valid. Our motives included, firstly, that no over-the-counter antibiotics are permitted in Sweden. Secondly, antibiotic prophylaxis continuing after the perioperative intravenous doses, is not recommended in Sweden . Thirdly, as most primary SSIs after DRF surgery are superficial and have an early onset [11, 16], the clinical praxis in the setting under study is peroral treatment primarily aimed at Staphylococcus aureus, with Flucloxacillin, or Clindamycin in case of penicillin allergy.
The time period after surgery during which the SPDR was screened for prescriptions of antibiotics was set to 8 weeks based on our clinical experience as well as previous research [18, 23, 37]. We are aware that by doing so, late onset SSIs occurring after 8 weeks were missed. However, based on our clinical experience we believe that late onset SSIs are rare in DRF surgery.
The study period encompassed 7 years, ending in 2013. We are aware that treatment trends have continued to change since 2013, with an increasing popularity of plate fixation over external fixation as the method of choice. However, we argue that by covering a time period during which external fixation was still one of the standard treatment methods for displaced non-complex DRFs, this study has provided comparative data for the main surgical methods, which is less susceptible to confounding by indication than more recent data would be.
A limitation of the NPR was its lack of detailed patient- and fracture-related data relevant to fracture treatment and complications (e.g. fracture side, fracture classification, tobacco use). Another potential limitation was the lack of validation of DRF codes in the NPR. Further, as patients with concomitant bilateral DRFs or a recurring DRF within the study period were only accounted for once, there was a risk of underestimating the number of fractures. Also, the NCSP-S code for plate fixation in the NPR is the same for volar, dorsal and multiple plating. While the standard approach for plate fixation of DRFs is volar, dorsal and multiple approaches are mainly used for a subset of complex DRFs. To not be able to separate these may have introduced bias. Lastly, the NCSP-S code for percutaneous pinning does not discriminate between pins buried under the skin or not, which also may have introduced bias. However, a recent Cochrane review of percutaneous pinning in the treatment of DRFs found very low-quality evidence that buried pins reduce the incidence of superficial SSIs .
The SPDR provides information on dispensed prescription drugs only. Thus, prescribed medications which are not dispensed are not registered in the SPDR. This may have caused an underestimation of the primary outcome in our study. Likewise, an overestimation of our primary outcome may have been caused by prophylactic prescription of antibiotics for postoperative swelling and pain without positive bacterial culture findings, as well as by prescription of Flucloxacillin and/or Clindamycin due to other infections unrelated to DRF surgery.
We did not extract the NCSP-S code for surgical debridement from the NPR file. Thus, in this register study we could not differ superficial SSIs manageable with only peroral antibiotics from deep infections requiring in-patient care, intravenous antibiotics and surgical debridement. However, deep SSIs which require surgical debridement and intravenous antibiotics are rare after DRF surgery . Furthermore, these patients are most likely prescribed peroral antibiotics at discharge and are thus included in our study population.