Electron Microprobe Analysis and Tissue Reaction around Titanium Alloy Spinal Implants

STUDY DESIGN A retrospective study of tissue surrounding titanium alloy spinal implants was performed using histological and electron microprobe analysis. PURPOSE To identify the metal debris generated by spinal implants, and then to evaluate the electron microprobe analysis results and the histological response of soft tissue surrounding the spinal implants. OVERVIEW OF LITERATURE Microscopic metal particles from the soft tissue surrounding joint arthroplasty have been shown to activate a macrophage response that leads to bone resorption and increased inflammation. The effect of unintended wear particles in spinal instrumentation remains a clinical concern. METHODS Ten patients (average age, 51.3 years), 6 men and 4 women, who had undergone previous lumbar fusions using pedicle screw instrumentation and who were now undergoing revision surgery were included in the study. The tissues obtained from the adjacent area of these implants were analyzed by light microscopy, immunohistochemistry and scanning electron microscope. After the removing the spinal implants, the changes of back pain and the spinal fusion were assessed. RESULTS There were metal particles in the soft tissue in 7 cases. Histological finding observed mild chronic inflammation surrounding the deposition of the metal particles and the anti Cotrel-Dubousset 68 positive macrophages were observed at tissue adjacent to the metal particles in 5 patients. Scanning electron microscopy of the specimens showed metallic debris within the tissue and mapping of the metallic particles revealed the distribution of titanium in the tissue in 5 cases. Nine patients had successful relief of back pain after removing the spinal implants. Improvement of the back pain may be an association macrophage response rather than the metal particle. CONCLUSIONS The presence of metallic particles generated from spinal implants may serve as the impetus for a late-onset inflammatory response and late operative site pain.