Late operative site pain with isola posterior instrumentation requiring implant removal - Infection or metal reaction?

Objectives. To elucidate the cause of late operative site pain in six cases of scoliosis managed with Isola posterior instrumentation that required removal of the implants. Method. Microbiologic examination of wound swabs and enriched culture of operative tissue specimens was undertaken in all cases. Histologic study of the peri-implant membranes also was conducted. Results. The presentation in all cases was similar: back pain appearing between 12-20 months after surgery, followed by a local wound swelling leading to a wound sinus. In only one of these cases was the discharge positive for bacterial growth. Implant removal was curative. Histologic examination of tissue specimens revealed a neutrophil-rich granulation tissue reaction suggestive of an infective etiology despite the failure to isolate organisms. Within the granulation tissue was metallic debris that varied from very sparse to abundant from fretting at the distal cross-connector junctions. A review of recent literature describing similar problems suggests that late onset spinal pain is a real entity and a major cause of implant removal. Conclusions. On reviewing the evidence for an infective etiology versus a metallurgic reaction etiology for these cases of late onset spinal pain, it was concluded that a subacute low-grade implant infection was the main cause. Histologic findings would seem to confirm low-grade infection. There may be more than one causative factor for late operative site pain, as it is possible that fretting at cross connection junctions may provide the environment for the incubation of dormant or inactive microbes.