Screw fixation in bone of guinea pigs sensitized to nickel and cobalt

A screw was inserted transversely through the distal femora and proximal tibiae of guinea pigs sensitized to either Ni or Co. An equal number of nonsensitized animals were treated in the same way. The animals with Ni allergy received an ASIF stainless steel screw and the animals with Co allergy a Howmedica Vitallium screw. After 6 weeks no obvious differences were observed in the histological picture around the femur screws that could be ascribed to metal sensitivity. The mechanical strength of the bone adjacent to the tibial screws was tested by measuring maximum torque during continuous tightening of the screws at a rate of 2 revolution/second. No significant differences in maximum torque resistance were found between sensitized and nonsensitized animals. The results indicate that sensitivity to Ni or Co does not compromise the mechanical fixation between metal and bone during the early period after the implantation.