Corrosion-Accelerated Mechanical Failure of a Vitallium Nail-Plate

¹ From the Department of Metallurgy and Materials Science, Massachusetts institute of Technology, Cambridge, and the Departments of Orthopaedic Surgery and Pathology, Massachusetts General Hospital, Boston

Analysis of a broken Vitallium nail-plate device which had been used to fix an intertrochanteric fracture of the hip revealed that the nail was composed of cast Vitallium and the plate of wrought Vitallium. Little or no plastic flow accompanied the failure of the plate, suggesting gross overloading was not the prime cause of implant fracture, although it would have probably occurred in this case if failure had not interceded. The condition of the fracture surface indicated that essentially brittle failure had occurred, and that the fracture crack had initiated from the region of nail-plate contact, even though such a region is normally in a state of compressive stress. The scanning electron microscope was used to examine all surfaces, and revealed the presence of microscopic cracks nucleated by corrosion pits in the nail-plate contact area. The pits were probably due to electrochemical action aggravated by the dissimilar metal contact, stress concentration, and crevice corrosion effect of the nail-plate contact area inherent in the implant design. These findings suggest that wrought and cast Vitallium should not be used in combination, even when only compressive stresses on the implant are involved.

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