Late-developing infection following posterior fusion for adolescent idiopathic scoliosis

This study is a retrospective case series review of patients with adolescent idiopathic scoliosis (AIS) who were revised more than 1 year after the index procedure, due to a late-developing deep wound infection, to determine onset, bacteriology, possible influence of implant alloy (titanium vs. stainless-steel) and treatment outcome of patients. From a total of 540 patients who underwent posterior-only fusion for AIS from 1993 through 2005 at our institution, 15 cases (2.77%) were revised due to a late-developing post-operative infection: there were six males and nine females, with an average age at initial surgery of 15.8 years (range 12-18). Late infections occurred at a mean of 70 months (15-95) after the index procedure. The implant alloy used was a stainless-steel instrumentation in 11 patients (4.56% of 241) and a titanium one in 4 patients (1.33% of 299): there was an higher incidence of late infections in stainless-steel alloy group of patients (P < 0.0001). Complete removal of instrumentation was performed in nine patients, obtaining in all cases wound healing and no symptoms of infection, at a minimum 3 years follow-up. In the other six patients, presenting less severe clinical signs of infections, an attempt to save/replace the previous instrumentation was performed, but a complete instrumentation removal had to be performed 11.6 months later (range 3-24) for the persistence or recurrence of infection: all patients healed uneventfully at a minimum 3 years follow-up. Intraoperative cultures were obtained in all 15 cases, being positive in 13 cases (S. epidermidis in 5 patients, S. aureus in 3, Propionibacterium acnes in 1, Serratia marcescens in 1, Propionibacterium acnes + S. epidermidis in 1, S. aureus + S. epidermidis in 1 and coagulase-negative Staphylococci in 1). None presented at latest follow-up scoliosis progression: there was no statistically significant difference between final and pre-operative revision surgery values (P = 0.17). In conclusion, treatment of late-developing post-operative infection in AIS surgery required complete removal of the implant, continuous drain and adequate antibiotic therapy based on intraoperative swab antibiogram. Titanium alloy instrumentations resulted less subject to late post-operative infections, when compared to stainless-steel ones (P < 0.0001).