Diaphyseal femoral and tibial fractures are in the spotlight within the traumatology-orthopedics scenario. Intramedullary nailing (IMN) remains the method of choice for treating these fractures, both open and closed ones. Occurrences of surgical site infection (SSI) related to this type of osteosynthesis are a challenge for all the professionals involved in patient healthcare. The reported incidence of SSI after IMN ranges from 0.9 to 17.5%. The majority of the data comes from retrospective studies and as part of case series descriptions, with little detail about the criteria used for defining and searching for cases of infection. Regarding the potential risk factors for this complication, previous use of external fixators, occurrence of open fractures and the severity of exposure according to the Gustilo-Anderson classification were indicated in a few retrospective studies as being possibly related to this complication. The objectives of the present observational cohort study are: 1. To determine the incidence of SSI related to IMN for fixation of diaphyseal femoral and tibial fractures in patients treated in a university traumatology and orthopedics reference hospital in São Paulo, Brazil; 2. To evaluate the risk factors related to the occurrence of this type of infection.

Diaphyseal femoral and tibial fractures are a important challenge faced by the orthopedic surgeon, due to their high incidence and high social and economic impact. Currently, the observed increases in the rates of injuries secondary to traffic, work and firearms-related accidents, and also those related to sports practice, have led to significant growth of the incidence of these fractures, especially among young and economically active individuals .

Although standardized criteria for indications of conservative treatment exist, surgery is often recommended due to its better functional results and shorter rehabilitation period. Intramedullary nailing (IMN) was introduced by Küntscher in 1939 and remains the method of choice for treating these fractures, both closed and open ones, especially because the surgical technique is considered to be simple, standardized and replicable; does not cause major soft tissue damage and allows early loading. This technique is associated with a higher consolidation rate and lower incidence of complications, among which infections are included.

Surgical site infection (SSI) after internal fracture fixation is considered to be a severe, hard-to-treat complication, and it is important to remember that the presence of the implant itself favors bacterial invasion and alters local immunity, thus hampering the action of granulocytes. In addition, injury to the soft tissues adjacent to the fracture focus also hampers this immunity and favors occurrence of infections.

Although complications are less frequent than in other internal fracture fixation methods, they can occur during the postoperative period, relating to the use of IMN, and these may include SSI. Its occurrence significantly increases recovery time and treatment costs, and it compromises the long-term functional results and rehabilitation.

SSIs, including those related to IMN, are defined internationally in accordance with the criteria established in the United States (USA) by the National Healthcare Safety Network (NHSN), an agency belonging to the Centers for Disease Control and Prevention (CDC). 8 This body is responsible for healthcare-related infection surveillance actions in that country. In Brazil, as in other countries, adaptations made by the local health and epidemiological surveillance authorities are followed.

In January 2015, the NHSN made available a document with new definitions of SSI, which came into force in the USA from that moment onwards, with important changes. The period for defining infections relating to fracture fixation procedures, regardless of the type of synthesis material used, became only 90 days, instead of one year from the data of the surgery. For better evaluation, however, for the present study, the surveillance period remains one year for defining SSIs relating to IMN.

Different incidences of SSI after fixation of lower-limb fractures through IMN have been reported in the literature. Most of these have come from retrospective studies and as part of the description of series of cases of patients who underwent this procedure, with little detail about the criteria used for defining and searching for SSI cases. Only two prospective studies have so far reported the occurrence of this complication: these studies were not specifically designed for evaluating SSI and only describe its occurrence superficially, among other complications . Until recently, only Gaebler et al., in 2000, had described this complication with greater methodological rigor. In 2015, however, because of the gap in knowledge that existed, three authors published the results from retrospective studies that had been specifically designed for evaluating SSIs relating to IMN for correcting lower-limb fractures. Despite this recent interest in this subject among researchers, there continue to be no prospective studies specifically designed for investigating the incidence of this complication, or its risk factors. In Latin America, in particular, there are no studies of any kind evaluating the incidence of SSI after fixation of lower-limb fractures using IMN.

Risk factors for occurrences of surgical site infections are generally divided into those relating to the host, the surgical environment and the microbiota. For occurrences of SSI after fracture fixation procedures, the following are considered also to be risk factors: degree of energy of the associated trauma, degree of injury of the adjacent soft tissues, degree of local contamination, duration of osteosynthesis surgery and immunological status of the patient.

However, specifically with regard to risk factors relating to occurrences of SSI after fixation of lower-limb fractures through IMN, information is scarce, given that the majority of the studies that analyzed the incidence of this complication did not allow for analysis of the risk factors relating to their occurrence. Until 2015, only Gaebler et al. had published results from an analysis on these risk factors. They concluded from their retrospective study that the risk of acquiring SSI after implantation of IMNs was 22.4 times higher among patients with Gustilo III open fractures than among patients with other types of fractures. However, these authors did not evaluate the importance of other factors that are considered to be associated with occurrences of SSI after fracture fixation.

Because of the lack of information on this important subject, in 2015 three authors published results from retrospective investigations that enabled a few conclusions. Galvin et al., in their study on closed tibial fractures in American soldiers, found higher incidence of SSI after IMN in patients who presented clinical instability during the initial care, although this difference was not statistically significant.

In turn, Metsemakers et al. concluded, after an initial univariate analysis, that previous use of external fixators, occurrences of open fractures and the severity of exposure according to Gustilo-Anderson would be factors associated with occurrences of SSI, as also would greater time intervals between the fracture and its fixation through IMN. It needs to be highlighted that these authors did not define the time interval above which the risk of infection would be greater. After multiple logistic regression analysis, however, only previous external fixation remained as a factor associated with occurrence of SSI after internal fixation of the fracture with IMN. In the study conducted by Roussignol et al., only the severity of the open fracture according to the Gustilo-Anderson classification had a statistically significant correlation with occurrences of infection. Other variables, including the severity according to the AO classification, previous external fixation, and time interval between fracture and its internal fixation did not present correlations with increased incidence of SSI associated with IMN.

It needs to be emphasized that none of the studies cited that presented information on the factors associated with occurrences of SSI after fracture fixation through IMN were prospective. This shows that the medical literature still lacks information obtained using greater methodological rigor.

Inclusion Criteria:

• Closed and open diaphyseal femoral and tibial fractures treated through IMN;
• Age: 16 years or older
• The patient or a person legally responsible for the patient should sign the free and informed consent statement (FICS) in order to take part in the study.

Exclusion Criteria:

• No exclusion criteria

Patients were included in the research after the surgical plan for intramedullary nailing for fixation of their fractures has been defined. This inclusion could occur up to 72 hours after the surgical procedure. If a patient presented more than one diaphyseal femoral or tibial fracture that could be potentially included in the study, only the first surgically corrected fracture were considered for analysis in the study.

221 patients were included and completed follow up

18 months

26 cases of infection were observed after 12 months of follow-up. One patient died from infection.

Hyperglicemia was not measured.