gms | German Medical Science

Objective: Peri-implant osteosarcoma (OSA) occurrence was found in dogs treated with the Slocum cast stainless steel tibial plateau leveling osteotomy (TPLO) plate. Recently, it was assumed that the metallurgical inhomogeneity of the plate surface, or the reduced corrosion resistance of the cast stainless steel material, were related to OSA occurrence. Therefore, the aim of the current study was to investigate the corrosion behavior of TPLO plate surfaces from animals with and without OSA.

Method: Eighteen retrieved 316L cast stainless steel Slocum TPLO plates, 9 from dogs with (CwOS) and 9 from dogs without peri-implant osteosarcoma (CnOS) were investigated. Three retrieved forged stainless steel TPLO plates (Synthes) from dogs without osteosarcoma (FnOS) represented a different manufacturing process. On all plates, visual inspections with a stereomicroscope and local micro electrochemical corrosion measurements were performed on plastic deformed surface areas in 1M NaCl on various spots (d=0.1mm) and corrosion resistance factors (CRF) were calculated. To assess the metallurgical inhomogeneity, nine randomly positioned corrosion measurements were performed on one plate of each group. The Mann-Whitney U Test was used for statistical analysis.

Results and conclusion: The time in-situ was comparable for both cast implant groups (CwOS 59±19 months vs. CnOS 52±14 months) and was shorter for FnOS (35±5 months). Microscopic inspections on the cast groups showed rough surfaces, residues and signs of local corrosion attacks. Furthermore, local notches and more severe tool marks were found next to the contoured regions of the plate. On the forged plates only few marks, but no residues or microscopic signs of corrosion could be detected. The CRF values determined on different surface spots showed a wide variation for the cast plates and a small bandwidth in forged plates; the differences between groups were significant (p<0.001). Repeated measurements on one plate of each group showed a significantly higher ion production for CwOS than for CnOS (p=0.008) or FnOS (p<0.001).

The local micro electrochemical corrosion measurements showed no clear difference between local corrosion behaviors of the two groups of cast plates due to a large standard deviation. The ion measurements clearly show a significant increase of ion release for the OSA group, which resembles the metallurgical inhomogeneity of the plate surface. Both corrosion and metal ion release result in chronic inflammation in the tissues with oncogenic effects; furthermore, direct toxic effects of these ions may also contribute to a foreign-body carcinogenesis. Despite our findings and their implications, there remains no clear evidence for a direct causal connection between the surface properties of cast plates, the local CRF and the occurrence of peri-implant OSA. Nevertheless, our results add to the speculation that OSA development might be related to local surface corrosion and the influence of that condition on neighboring bone cells.