Bacterial Phenotype of Staphylococcus Aureus Has no Effect on Patients' Clinical Outcome in Orthopedic Device Related Bone Infections
Bacterial Phenotype of Staphylococcus Aureus Has no Effect on Patients' Clinical Outcome in Orthopedic Device Related Bone Infections
This was a prospective study performed between November 2011 and September 2013. Patients
 with a confirmed S. aureus infection after fracture fixation or prosthetic joint infection
 were included. Exclusion criteria included infections involving external fixation pins,
 infections without any implanted hardware and culture positive patients not displaying any
 clinical sign of infection. The following surgical parameters were documented: affected bone
 or joint; type of implant; time between implantation of the device and onset of symptoms.
 Personal characteristics and patients'health status were also documented. Any revision
 surgeries involving the site of interest and all isolated pathogens were recorded throughout
 the course of treatment and follow-up.

 A follow up examination was performed an average of 23 months after discharge. Primary
 outcome at follow up was cure. Cure was defined by the authors as: missing local (at site of
 interest) or systemic signs of infection, terminated surgical and systemic therapy and
 restoration of joint or limb function.

 At the first surgical procedure after enrolment, at least four deep bone biopsies were taken
 from the interface between implant and affected bone. Identification and antibiotic
 susceptibility testing of all growth was performed. Multi-drug-resistance (MDR) was defined
 according to the definitions of the European Committee of Antimicrobial Susceptibility
 Testing (EUCAST). Biofilm formation was analysed and quantified in microtitre plate assays
 according to protocol of Stepanovic et al.(see references).
This was a prospective study performed between November 2011 and September 2013. All patients
 provided informed written consent prior to inclusion in the study. Inclusion criteria were
 deep S. aureus infections after fracture fixation or prosthetic joint surgery. Fracture
 fixation infections includes fractures involving the long bones as well as the pelvis and the
 spine. Bacterial growth at the site of interest in combination with either pseudarthrosis,
 implant-loosening/failure or local and systemic signs of surgical site infection were
 required for inclusion. Exclusion criteria included infections involving external fixation
 pins, infections without any implanted hardware and culture positive patients not displaying
 any clinical sign of infection.

 Upon entry into the study, the following surgical parameters were documented: affected bone
 or joint; type of implant; time between implantation of the device and onset of symptoms.
 Personal characteristics were also documented and included: gender; age; body mass index
 (BMI); smoker/non-smoker; overall medical condition (Charlson comorbidity index); and chronic
 immunosuppressive conditions (Diabetes mellitus, chronic alcoholism, Child's class C
 cirrhosis, neoplasia, transplantation, AIDS and steroid medication). Any revision surgeries
 involving the site of interest and all isolated pathogens were recorded throughout the course
 of treatment and follow-up.

 A follow up examination was performed an average of 23 months after discharge. Primary
 outcome at follow up was cure. Cure was defined by the authors as: missing local (at site of
 interest) or systemic signs of infection and terminated surgical and systemic therapy.

 At the first surgical procedure after enrolment, at least four deep bone biopsies were taken
 from the interface between implant and affected bone. The tissue samples were placed in a
 sterile container with thioglycollate liquid medium (bioMérieux, Hazelwood, MO, USA). The
 samples were cultured for ten days at 37°C and examined each day macroscopically. Any growth
 was inoculated onto a blood agar plate (bioMérieux, Hazelwood, MO, USA) for further growth
 and subsequent identification. In all cases, additional swabs and soft tissue samples may
 have been taken as per clinical routine, however, only samples adjacent to the implant were
 used for diagnosis in this study.

 Identification and antibiotic susceptibility testing of all growth was performed using a
 Vitek2 (bioMerieux Vitek Inc, Hazelwood, MO, USA). Multi-drug-resistance (MDR) was defined
 according to the definitions of the European Committee of Antimicrobial Susceptibility
 Testing (EUCAST). Oxacillin resistance was used as an indicator for methicillin resistant S.
 aureus (MRSA).

 Biofilm formation was analysed and quantified in microtitre plate assays according to the
 well-established protocol of Stepanovic et al.(see references).

 The key variables with regards to bacterial phenotype were: biofilm formation; methicillin
 resistance;multidrug resistance;staphyloxanthin production and hemolysis. The primary outcome
 measure was whether the infection was "cured" or not. Primary outcome parameters were
 calculated as a function of all patients for whom data was complete. Statistical comparison
 was restricted to the lower extremity cohort since the other patients are not scored for many
 of the functional outcome measures and as such incomplete.

 Univariate logistic regression models were used to determine the influence of each prognostic
 factor (obesity, smoking, diabetes mellitus, chronic immune suppression, open fracture
 (initially), early onset infection, biofilm formation, methicillin resistance, MDR and
 Charlson comorbidity index) on cure. P-values <0.05 were considered significant. Statistical
 analyses were performed using SAS software (Version 9.2; Cary, NC, USA).
Inclusion Criteria:

 -  Infections after fracture fixation or prosthetic joint surgery

 -  Affected bone or joint: Long bones of the lower and upper extremity

 -  Bacterial growth of S. aureus at the site of interest

 -  Written consent

 -  Age: 18 and older

 Exclusion Criteria:

 -  no prove of bacterial growth at site of interest

 -  missing consent

 -  infections involving external fixation pins, infections without any implanted
 hardware.