ABSTRACT
PURPOSE: Skeletal metastases affect up to 85% of breast cancer patients by the time of their death. This prospective in vivo study evaluated the diagnostic performance of computed tomography-based structural rigidity analysis (CTRA) to predict vertebral fracture risk in breast cancer patients with skeletal metastasis and in comparison with the current standard of care. EXPERIMENTAL DESIGN: Torso CT scans of 94 women with vertebral metastatic breast cancer were obtained as part of routine screening for lung and liver metastases. The load-bearing capacity (LBC) and axial (EA) and bending (EI) rigidities of vertebrae T8 to L5 were calculated from CT images. The LBC was normalized by patient body mass index (BMI) to account for height and mass variations. Vertebral fracture risk was also calculated using the current radiographic-based criteria based on lesion size and location. The actual occurrence of a new vertebral fracture was assessed radiographically over the ensuing 4 months. RESULTS: Eleven vertebral fractures occurred in 10 patients. The structural parameters EA, EI, LBC, and LBC/BMI were all 100% sensitive and 55%, 53%, 44%, and 70% specific to predict fracture risk, respectively. Although radiographic criteria correctly predicted all fracture cases (100% sensitive), only 48 of the 236 spinal segments that did not have a fracture were correctly predicted not to fracture (20% specific). CONCLUSIONS: CTRA, using CT scans as part of routine screening for lung and liver metastasis, is shown to be as sensitive as, and significantly more specific than, the current radiographic criteria for predicting vertebral fracture in breast cancer patients with skeletal metastasis. (Clin Cancer Res 2009;15(24):7676-83).
ABSTRACT
BACKGROUND CONTEXT: Surgeons are hesitant to mix components made of differing metal classes for fear of galvanic corrosion complications. However, in vitro studies have failed to show a significant potential for galvanic corrosion between titanium and stainless steel, the two primary metallic alloys used for spinal implants. Galvanic corrosion resulting from metal mixing has not been described in the literature for spinal implant systems. PURPOSE: To determine whether galvanic potential significantly affects in vitro corrosion of titanium and stainless steel spinal implant components during cyclical compression bending. STUDY DESIGN/SETTING: Bilateral spinal implant constructs consisting of pedicle screws, slotted connectors, 6.35-mm diameter rods and a transverse rod connector assembled in polyethylene test blocks were tested in vitro. Two constructs had stainless steel rods with mixed stainless steel (SS-SS) and titanium (SS-Ti) components, and two constructs had titanium rods with mixed stainless steel (Ti-SS) and titanium (Ti-Ti) components. METHODS: Each construct was immersed in phosphate-buffered saline (pH 7.4) at 37 C and tested in cyclic compression bending using a sinusoidal load-controlling function with a peak load of 300 N and a frequency of 5 Hz until a level of 5 million cycles was reached. The samples were then removed and analyzed visually for evidence of corrosion. In addition, scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) were used to evaluate the extent of corrosion at the interconnections. RESULTS: None of the constructs failed during testing. Gross observation of the implant components after disassembly revealed that no corrosion had occurred on the surface of the implants that had not been in contact with another component. The Ti-Ti interfaces showed some minor signs of corrosion only detectable using SEM and EDS. The greatest amount of corrosion occurred at the SS-SS interfaces and was qualitatively less at the SS-Ti and Ti-SS interfaces. CONCLUSIONS: The results from this study indicate that when loaded dynamically in saline, stainless steel implant components have a greater susceptibility to corrosion than titanium. Furthermore, the galvanic potential between the dissimilar metals does not cause a discernible effect on the corrosion of either. Although the mixture of titanium alloy with stainless steel is not advocated, the results of this study suggest that galvanic corrosion is less pronounced in SS-Ti mixed interfaces than in all stainless steel constructs.