A recent advancement in the design of the total artificial hip is the introduction of modularity. Within the last year clinical retrievals have shown that significant corrosion can occur at the cone-taper interface in some variations of the modular hip. The hypothesis of this study was that the stability of the cone-taper interface affects the amount of fretting corrosion that occurs. The development of a method that can study the taper corrosion and determine the most stable design is therefore necessary.
Design characteristics that may affect corrosion include the use of dissimilar metals, taper angle, taper diameter, percent coverage, machining tolerance, and head neck extension. The fretting that occurred at the interface was initially studied by measuring potential changes while cyclically loading hips in a universal testing machine. This method of measurement proved ineffective at isolating the fretting at the taper interface so current changes were monitored instead. The current was measured when the saline was below the crevice and when it was just above the crevice, and the two measurements were subtracted from each other to produce the taper fretting current.
When comparing two different designs, one showed a significant taper fretting current while the other's was minimal. In a second study, when comparing two different head neck extensions placed on identical stem designs, a significant taper fretting current was seen with the + 10-mm head as compared to a +0-mm head. It is concluded that this method can be used in the evaluation of designs to optimize stability and reduce the resulting fretting corrosion.