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Objective:
Surgical site infections (SSI) in patients with posterior spinal instrumentation pose a challenge to the patients, the treating physicians and the health care system. Literature on the most appropriate treatment is scarce and data on the need for removal of implants are contradictory. Therefore, we retrospectively analysed the management and clinical outcome of such patients at our institution.

Methods:
Our in-house databases of prospectively documented surgeries and infectious diseases were searched for eligible patients (01/2008-06/2018). Patient files were reviewed for age, gender, BMI, smoking status, medical history, details of surgery (duration, local antibiotics, debridement and implant retention (DAIR), partial (-cage) or complete (+cage) implant removal/exchange), causative pathogens, antimicrobial treatment, and outcome. Infection outcome was assessed in patients with ≥1 year follow-up (FU) (healed=no revision & no suspected signs of infection; surgical failure (sf)=non-septic revision; relapse=readmission for septic revision with same pathogen; new infection=new pathogen on septic revision; cure=healed & sf). Patient-reported outcome (PRO) was documented with the Core Outcome Measures Index (COMI) assessing pain on a 10-point scale, function, well-being, quality of life, disability.

Results:
172 patients (31.8% male; 65.3±12.8y; BMI 29.3±5.6 kg.m-2, 23.0% smokers) underwent 214 revisions for 178 SSI. Median time between index and revision surgery was 23d (7d –11y). In 65% (139/214) deep subfascial infection was macroscopically diagnosed intraoperatively. The most commonly isolated pathogens were Staphylococcus epidermidis (n=80, 37.4%) and Staphylococcus aureus (n=56, 26.2%); n=28 polymicrobial (13.1%). DAIR was done in 136/214 (63.6%) surgeries, partial removal/exchange of loose implants in 61/214 (28.5%), and complete removal/exchange in 14/214 (28.5%); missing n=3 (1.4%). Persistent infection required multiple revisions (up to 4) in 29/178 SSI (16.3%). Surgery was followed by intravenous and oral antimicrobial treatment for 10-12 weeks.
In the 136 SSI (76.4%) with ≥1-y FU, infection was cured in 113 (83.1%); relapse occurred in 9 cases (relapse rate: 6.6%). Two patients (1.4%) died due to uncontrolled infection. COMI decreased significantly (p<0.001) from 8.2±1.5 before treatment to 4.8±2.9 at the 1y-FU. A significant reduction in pain was noted within the first year (backpain: 6.7±2.3 vs. 3.7±2.8, legpain: 5.8±3.3 vs. 3.1±2.8, p < 0.001). 93.3% of patients with a completed COMI (n=112/120) were satisfied with the overall treatment received.

Conclusion:
In most cases, patients with SSI after posterior spinal instrumentation can be successfully treated with optimal surgical and antibiotic treatment. Implants could be retained in the majority of cases. Multiple revisions may be necessary in selected cases. PRO are satisfactory. These results may serve for future establishment of treatment algorithms and patient information.