Metallic Ion Release from Corrosion of Cast Stainless Steel TPLO Implants Is Implicated in Osteosarcoma Development in Dogs: A Focal Electrochemical Analysis

Introduction:
Implant corrosion and ion release are associated with tumor development. Cast 316L stainless steel plates previously used in dogs in the TPLO procedure undergo considerable corrosion that was suggested to result in peri-implant osteosarcoma (OSA).

Materials and Methods:
Focal electrochemical surface properties (spot diameter 100um) of cast plates retrieved from dogs with/without peri-implant OSA were investigated. Electrochemical variations due to corrosion were assessed to calculate local metallic ion release. Retrieved forged implants without peri-implant OSA served as controls.

Results:
Cast plates demonstrated inhomogeneous superficial composition with high spatial variability of the electrochemical surface properties. This effect was increased in plastic deformed regions of the plates (intra-operative contouring). Ion release in cast plates at non-deformed locations showed generally lower values and larger variation compared to deformed locations, although not statistically significant. All cast plates showed significantly higher ion release than forged plates at non- deformed (p=0.025) and deformed (p=0.022) surface regions compared to forged plates. No correlation between ion release and OSA development could be confirmed; however, significantly greater ion release was observed with cast plates (p=0.008), or cast plates with OSA (p<0.001) and without OSA (p=0.011) compared to forged plates.

Discussion/Conclusion:
The cast implants underwent localized corrosion resulting in greater metallic ion release than corresponding forged implants. The biological interpretation suggests that tumour development is more likely to occur in these areas as a result of chronic inflammation and the direct toxic effects of the accumulated ions. This corrosion behaviour may trigger neoplastic transformation of cells adjacent to these implant surfaces.