Late-developing infection in instrumented idiopathic scoliosis

Study Design. This is a retrospective review of all patients requiring either Cotrel-Dubousset or Moss Miami rod removal. All initial spinal instrumentations were for adolescent idiopathic scoliosis from 1985 through 1994. Twenty-two patients who underwent rod removal for late-developing infection constitute the study group. Objectives. To determine the bacteriology and treatment of patients with late-developing infection after posterior spinal instrumentation for scoliosis. Summary of Background Data. There have been conflicting reports regarding this entity, some reporting a high percentage of positive cultures and others a low yield. The latter have attributed the entity to fretting corrosion. Much literature describes late appearance of infection with large foreign bodies (implants). Glycocalyx, a membrane that surrounds bacteria adjacent to surgical implants, results in poor antibiotic penetration, poor macrophage action, and difficulty in culturing bacteria. Methods. One thousand two hundred forty-seven patients who underwent posterior instrumentation from 1985 through 1994 were reviewed. Those requiring implant removal were further studied. Those with late-developing infection (more than 1 year after the initial procedure) were further reviewed. Culture reports, presence of pseudarthrosis, and antibiotic regimen after implant removal were the primary parameters studied. Results. Twenty-two patients (1.7%) experienced development of late infection a mean of 3.1 years after the initial procedure. In specimens from these patients cultured only 72 hours, only 1 of 10 was positive. Of those cultured for 7-10 days (the last 12) 11 were positive, usually for low-virulence skin organisms. After surgery, patients received antibiotics parenterally for 48 hours and orally for 7 days. All wounds were closed primarily. Four patients had pseudarthroses, two underwent revised procedures with titanium implants without signs of infection at more than 2 years' follow-up. Conclusions. Late-appearing infection with spinal instrumentation can be treated with device removal, primary skin closure, and short-term oral antibiotics. The infections affect soft tissue, not the bone.