Three cases of metallosis associated with spine instrumentation

The characteristic trait of metallosis is the presence of tissue staining. Analyzing explanted revision hardware from spine surgeries and performing ICPMS/AES analysis on removed tissue samples, a clinically relevant definition for metallosis may be developed. Results of the analysis identified hardware fretting wear and corrosion, and ICP-MS/AES analysis identified elevated metal ion concentrations in all cases. This supports the hypothesis that corrosion may be linked to poor health outcomes and potential need for revision surgery. Using failure analysis methods, corrosion products from orthopedic spine implants can be identified to begin to characterize metallosis in a clinically relevant manner. Failure analysis for patients undergoing revision spine surgery for other causes. Using failure analysis methods we conducted a retrieval analysis of explanted hardware and tissue. Implant failure with surrounding tissue metal staining is a current issue in the field of orthopedics. Specifically in spine, this issue is under reported and over looked as a clinically significant finding. Metallosis is most commonly used to describe the presence of tissue staining however this is not a clinically relevant definition. There is a need for further research to provide a better understanding of metallosis leading to better patient outcomes. Patients were screened for this study during a radiological review prior to surgery. All explanted hardware was documented and inspected for signs of wear and corrosion using non-destructive testing. A tissue sample that is normally removed and discarded was collected for ICP-MS/AES analysis. The presence of fretting corrosion, galling and corrosion fatigue was found on all explanted hardware. Cr levels are significantly higher than what was previously published as normal in muscle 0.03  μg/g. One case was a 4 order of magnitude elevation with the other 2 approximately 2 orders of magnitude increase. Titanium and Co concentrations are also significantly increased. The Ca to P ratio for all samples is approximately 1.7:1 suggesting some form of apatitic crystal present due to drying of the tissues. In all cases, the Al, Mo, V, Co, content in surrounding tissue is significantly elevated >10× above "normal," 8.4 ± 4.8; 1.61 ± 1.41; 0.06 ± 0.03; 1.35 ± 1.97 μg/g respectively. A "normal" reference titanium level could only be found for whole blood, 0.00072 ± 0.1412 μ/g. Iron and Ni measurements are within typical values presented in previous studies. No single mechanism for the release of metal ion in a patient is clear. Evidence suggests a tribocorrosive process due to both wear and environmental factors. Specific biologic mechanisms, such as the possible presence of bacteria may affect the fretting and corrosion of spinal instrumentation must be explored in conjunction with thorough review of patient outcomes. Such an effort can potentially reduce patient readmission and increase successful patient outcomes. Graphics abstract: