Metalloma from Wear Between a Cobalt-Chromium Rod and Titanium Screws

Study Design: Case report Objective: The aim of this study was to evaluate the etiology of metallosis/metalloma in spinal fusion through a case observation and literature review. Summary of literature review: Metalloma is observed in artificial joint replacement, even including spinal arthroplasty, but rarely occurs after fusion surgery of the spine, as movements are limited. The erosive mechanisms involve a multifaceted interplay of mechanical wear and corrosion. Materials and Methods: A 60-year-old man developed low back pain with lower-limb radiculopathy 2 years after L1-S1 fusion surgery using titanium (pedicle and set) screws and a cobalt-chromium rod with an interbody cage at L2-L3, L3-L4, and L4-L5. Radiographic assessment revealed non-union at L5-S1. Magnetic resonance imaging showed an intraspinal mass at S1 compressing the thecal sac. In revision exploration, dark gray granulation tissue was confirmed to be metalloma in histopathological examination. Results: After removal of the metalloma mass and bone grafting, along with set screw revision at S1, the patient was pain-free in his activities of daily living at the latest 6-month postoperative follow-up. Conclusions: Our report and literature review highlight the need for diagnostic suspicion, especially in the presence of differential material properties of combined implants. Inadequate fusion is another factor to consider, as it may increase the risk of metallosis development.