Fractured Whiteside Ortholoc II knee components

A comprehensive failure analysis was performed-on 6 femoral components and 1 tibial component that fractured in service. All were Whiteside Ortholoc I I total knee arthroplasty components, manufactured from cast cobalt-chromiu m-molybdenum alloy and porous coated. Fracture surface analysis revealed fa tigue-induced failure in all cases. Most fractures occurred at regions of h igh stress concentration, such as sharp corners, sintered beads, and thin s ections. Metallurgical examination showed significant variation in grain si ze, interdendritic carbides, and hardness between samples. In some cases, c ontinuous carbide networks and voids were prominent at the bead-substrate i nterface. Patient weight and surgical placement were identified as contribu tory factors in component failure. Limitations of cast cobalt-chromium-moly bdenum alloy in weight-bearing applications must be emphasized, particularl y when important determinants, such as design, metallurgy, and specific cli nical factors, are less than optimal.