Corrosion on an internal spinal fixator system

Study Design. Thirteen spinal fixators with 26 stabilization bridges and 52 pedicle screws and a mean length of implantation of 10 months were prospectively examined for corrosion. Objectives. To determine the type of corrosion and the correlation between the construction of the spinal fixator and the type of corrosion. Summary of Background Data. Evidence of fretting and crevice corrosion is seen in many stainless steel implants in retrieval studies. Such reactions have not been described in the literature on spinal fixator systems. Methods. Macroscopic and microscopic alterations in the adjacent tissue were examined, and the corrosive alterations were documented photographically using stereoscopic optical light microscopy. The chemical composition of the implants was determined spectrographically. Microradiography and x-ray fluorescence analysis of the soft tissue were performed. Results. At surgery, tissue discoloration was found in four cases. Histologic examination showed extensive fibrosis, foreign body reaction and inflammation associated with a small number of metal particles, indicating metallosis in five cases. Corresponding particles were detected by microradiography. Corrosion was found on 13 telescopic rods and on two pedicle screws. The alterations on the telescopic rods could be interpreted as crevice corrosion and the alterations in the pedicle screws as fretting corrosion. The two monobloc fixator bridges did not show signs of corrosion. In these implants, the neigh boring tissue was macroscopically inconspicuous, and histologic examination showed minimal fibrosis or presence of metal particles. Spectrographic examination of the spinal fixators showed no structural imperfection. Conclusions. The construction constraints of a spinal fixator make it prone to corrosion. New spinal implants should be examined not only in vitro but also in vivo to ascertain whether corrosion and adjacent tissue reaction occur. Corrosion is one reason to explant the internal fixation system after fusion of the spinal fracture