The tradeoffs associated with modular hip prostheses.

In an effort to gain greater insight into the tradeoffs associated with modular hip prostheses, 2 approaches were taken. A questionnaire was sent to each of the orthopaedic implant manufacturing companies asking specific questions regarding modular components, and a series of retrieved prostheses, both modular and nonmodular, were examined to determine the potential sources of problems associated with modular connections. The respondents to the questionnaire generally agreed that it was more expensive to produce modular prostheses due to the required tolerances at the modular connections, and that the increased flexibility provided by the modularity was important to surgical outcome. There was less consensus on whether inventories were reduced and little data to support any improvement in surgical outcome caused by modularity. The most frequent problems associated with modular connections were fretting and corrosion. Easily observable significant fretting occurred in 4% of 701 head/neck tapers. Corrosion was observed in > 30% of the mixed-alloy head/stem combinations, in < 10% of all-titanium-alloy modular components, and in < 6% of all-cobalt-alloy devices. In 1 series of retrieved modular femoral components (15 titanium alloy and 15 cobalt alloy) with both sets having approximately the same duration of implantation, 7% of the all-cobalt-alloy components had corrosion, whereas 33% of the mixed-alloy components had corrosion.