Impact of Surgical Site Infection To Outcome In Patients With Operatively Treated Tibial Plateau Fractures– A Retrospective Multicenter Study

Ralf Henkelmann (  ralf.henkelmann@medizin.uni-leipzig.de ) University of Leipzig, Clinic of Orthopedic, Trauma and Plastic Surgery https://orcid.org/0000-0001-52741896 Karl-Heinz Frosch University Hospital Hamburg-Eppendorf: Universitatsklinikum Hamburg-Eppendorf Richard Glaab Canton Hospital: Kantonsspital Aarau AG Meinhard Mende University of Leipzig Faculty of Medicine: Universitat Leipzig Medizinische Fakultat Christopher Ull Berufsgenossenschaftliche Kliniken Bergmannsheil: Berufsgenossenschaftliches Universitatsklinikum Bergmannsheil Philipp-Johannes Braun Unfallkrankenhaus Berlin Tobias J. Gensior Orthopädische Gemeinschaftspraxis Neuss Christoph Katthagen University Hospital Munster: Universitatsklinikum Munster Pierre Hepp University Hospital Leipzig: Universitatsklinikum Leipzig


Background
The goal of the surgical treatment of tibial plateau fractures (TPF) is to achieve the best level of mobility and quality of life postoperatively. However, the postoperative outcome depends on many factors. The initial surgical treatment strategy is determined by the fracture morphology, soft tissue damage, concomitant injuries and the general condition of the patient. In the early postoperative phase surgical site infection (SSI) is the most feared complication. Average SSI rates of 4.5% and more were described. [1] [2] [3] In a systematic review it was shown that only 44% have a satisfactory outcome after a deep SSI. [4] Focus of the most studies is to evaluate the generell outcome of tibial plateau fractures. [5][6][7][8] The aim of the here presented study was to evalute the impact of SSI on the outcome after operatively treated TPF measured with patient reported outcome scores.

Study design
We performed a retrospective multicenter study at seven level I trauma centers in Germany and Switzerland. The study was approved by the leading ethical committee of the XX and all corresponding ethic committees of the participating centers. Setting / Study size All patients who had surgical treated tibial plateau fracture in one of the hospitals from January 2005 through December 2014 were identi ed by querying the hospitals database with the International Classi cation of Disease (ICD) code for proximal tibia fractures. To avoid an inclusion of patients which were improperly coded, primarily operated in another hospital or were not in accordance with our inclusion and exclusion criteria charts were screened manually of every patient. All variables to be recorded were speci ed in advance and communicated to all participating centres in a pre-prepared spreadsheet.

Participants
Inclusion criteria are: aged > 18, primarily treated in one of the hospitals, proximal tibia fracture according to AO/OTA 41 B or C. [9] Exclusion criteria are: previous surgery at fracture site in another hospital, AO 41 A fractures, pathological fractures Variables / Data sources / measurements In addition to the standard parameters (age, sex, etc.), comorbidities were categorized into 4 groups according to the number of comorbidities: none, 1-3 comorbidities, 4-5 comorbidities, ≥ 6 comorbidities. The variables diabetes mellitus, nicotine abuse, alcohol/drug abuse as well as immunosuppressive drugs were listed separately at nominal scale level.
Accompanying injuries to the affected knee joint were classi ed as none, not relevant (abrasions, soft tissue injuries grade 1 according to Gustillo and Anderson) and relevant (further fractures of the affected extremity, compartment syndrome). Other concomitant injuries were categorized as none, not relevant (hematoma, abrasions, craniocerebral trauma grade 1) and relevant (fracture to other body region, craniocerebral trauma > 1 grade). Furthermore, patients with an Injury Severity Score (ISS) > 16 were classi ed as polytrauma. [10] The fracture morphology was classi ed according to the AO/OTA classi cation. [9] Furthermore, the variables open fracture and compartment syndrome were considered. SSI was recorded according to the de nition proposed by the current protocol of the National Healthcare Safety Network, Centers for Disease Control and Prevention (CDC). These de nitions are used in the German guideline of the Robert Koch-Institut (RKI) as well as by the WHO [11]. ) and Lysholm score. [12][13][14] For the KOOS5 score (maximum 100), a lower score represented more symptoms or pain, greater di culty performing ADLs and Sport/Rec, and poorer QoL. This rating also is valid for the Lysholm score (maximum 100).
A minimum follow-up was determined at 12 months postoperatively. A follow-up examination of the patient group with a SSI was performed in all participating centers. A reference group with patients without SSI was conducted by the additional follow-up examination of patients in three centers.

Bias
Due to the retrospective study design and the large number of study centers, it is possible that patients with an SSI may not have returned to one of the study centers for further treatment. Thus, the number of SSIs may be higher and the in uence of a higher number of patients with SSIs may have an impact on the results.
All patients with SSIs were contacted and followed up by telephone or post. Patients without SSI were included in three centers on the same procedure.

Statistical methods
The study cohort was characterized by standard statistics: Mean value (standard deviation) for continuous data, number (percent) for categorical data. Patient groups with and without infection were compared using ttest for continuous measurements and chi-square tests without correction for cross tables. All tests were performed two-sided to the signi cance level α = 0.05. The analyses were performed with IBM SPSS Statistics version 24 software.

Participants
Between January 2005 and Deceber 2014, 2106 patients were included in the overall study with 94 patients with SSI, which corresponds to a rate of 4.5%.
Of those 94 patients, 41 could be evaluated according to the study protocol (43.6%). As a reference group, 246 patients without SSI with follow-up were included in three centers (37.0%). In summary, 287 patients with an average follow-up of 75.9 ± 35.9 months (14-146) were included in this study (Fig. 1).

Descriptive Data
Basic demographic data for the collective and the two subgroups (SSI, without SSI) are presented in Tables 1  and 2. Patients in the overall group were on average 50.7 years old, had a BMI of 26.8 and a ratio of women of 49.1%. There was no signi cant difference between the groups in terms of age, Diabetes mellitus, BMI and comorbidities. Furthermore, there was a signi cant difference in body weight, sex, smoking and drug abuse between the groups (Table 1). There was a signi cantly higher proportion of C fractures in the SSI group. Also in the subgroups, the SSI group showed a signi cantly more complex fracture morphology. Signi cantly more patients were polytraumatized or had a relevant concomitant injury to the affected knee joint or other body region. Open fractures or compartment syndrome were signi cantly more frequent in the SSI group (Table 2). In surgical care, an external xator was applied signi cantly more frequently in patients with an SSI. A list of the primary surgical procedures in both groups and in the overall group is shown in Table 3.

Discussion
The aim of this study was to evaluate the outcome of patients with operatively treated TPF with SSI compared to patients without SSI using established and validated PROs. In terms of PRO, a signi cantly poorer outcome was recorded in patients with SSI. Furthermore, our analysis showed that patients with SSI differed signi cantly from patients without SSI in terms of gender, smoking and drug addiction. Additionally the trauma-associated factors showed a signi cant difference in the severity of fracture morphology, concomitant injuries (especially open fracture and compartment syndrome), and the incidence of polytraumata between the groups. The in uence of some of these factors on the development of an SSI has already been demonstrated by us hence a distribution of these factors in the groups was to be expected. [15] In general TPF can be life-changing injuries for concerned patients. This can be additionally highlighted by our data compared to KOOS or Lysholm reference data from a healthy population. [14,16] However, an SSI signi cantly further worsens the outcome. We have already been able to show in a systematic review that an infection is associated with a poor outcome. [4] But the in uence of SSI has not yet been investigated in multiple studies with PROs. Van  and movement limitation as well as the impairment of the periarticular soft tissues by multiple revisions could mainly be responsible for this. In general a return to sport is often very di cult after TPF as also shown in other studies and may explain why there was no difference between the groups. [5][6][7] Also the Lysholm Score con rmed the negative in uence of an infection on the outcome. Finally, our data showed that an SSI is responsible for a poor outcome after surgical treatment of a TPF regardless of other risk or in uencing factors. These strong results show that in addition to optimal fracture reduction and postoperative management, the avoidance of SSI has the greatest impact on a good outcome in TPF.

Limitations
The strongest limitation is the retrospective study design. Epidemiological data were complete from all participating centers, but only a small number of patients could be obtained for follow-up (43.6% and 37.0%).
Due to this small number of responders, a bias cannot be excluded. However, in terms of epidemiological data, there was no signi cant difference between the groups with and without SSI in terms of with and without followup. This study was performed in line with the principles of the Declaration of Helsinki. The study was approved by the leading ethical committee of the University of Leipzig (Reference number: 098/15-ff) and by the corresponding ethics committees of all participating hospitals. Patients gave their written consent to participate in the study after receiving appropriate information.

Consent for publication
Not applicable.

Availability of data and materials
The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Con ict of interest
The authors declare that they have no con ict of interest Funding None.
Authors' contributions RH and PH were responsible for data control and study supervision. The rst draft of the manuscript was written by RH and PH; all authors commented on previous versions of the manuscript. All authors read and approved the nal manuscript. RH, TG, CU, PJB, CK, RG, and KHF performed the data acquisition and data control in each trial site and obtained the respective approval of the responsible ethics committee. MM performed data curation, formal analysis, validation, and visualization of the study data, as well as further review and revision of the manuscript. PH and RH were responsible for project coordination.