METAL RELEASE IN PATIENTS WHO HAVE HAS A PRIMARY TOTAL HIP-ARTHROPLASTY - A PROSPECTIVE, CONTROLLED, LONGITUDINAL-STUDY

There is an increasing recognition that, in the long term, total joint replacement may be associated with adverse local and remote tissue re sponses that are mediated by the degradation products of prosthetic ma terials. Particular interest has centered on the metal-degradation pro ducts of total joint replacements because of the known toxicities of t he metal elements that make up the alloys used in the implants. We mea sured the concentrations of titanium, aluminum, cobalt, and chromium i n the serum and the concentration of chromium in the urine of seventy- five patients during a three-year prospective, longitudinal study, Twe nty patients had had a so-called hybrid total hip replacement (inserti on of a modular cobalt-ahoy femoral stem and head with cement and a ti tanium acetabular cup without cement), fifteen had had insertion of an extensively porous-coated cobalt-alloy stem with a cobalt-alloy head and a titanium-alloy socket without cement, and twenty had had inserti on of a proximally porous-coated titanium-alloy stem with a cobalt-aho y head and a titanium socket without cement. The remaining twenty pati ents did not have an implant and served as controls, The results of ou r study showed that, thirty-six months postoperatively, patients who h ave a well functioning prosthesis with components containing titanium have as much as a threefold increase in the concentration of titanium in the serum and those who have a well functioning prosthesis with cob alt-ahoy components have as much as a fivefold and an eightfold increa se in the concentrations of chromium in the serum and urine, respectiv ely. The predominant source of the disseminated chromium-degradation p roducts is probably the modular head-neck junction and may be a functi on of the geometry of the coupling, Passive dissolution of extensively porous-coated cobalt-alloy stems was not found to be a dominant mode of metal release, CLINICAL RELEVANCE: Increased concentrations of circ ulating metal-degradation products derived from orthopaedic implants m ay have deleterious biological effects over the long term that warrant investigation, This is a particularly timely concern because of recen t clinical trends, including the reintroduction of metal-on-metal bear ing surfaces and the increasing popularity of extensively porous-coate d devices with large surface areas of exposed metal. Accurate monitori ng of the concentrations of metal in the serum and urine after total h ip replacement also can provide insights into the mechanisms of metal release, Our findings suggest that fretting corrosion at the head-neck coupling is an important source of metal release that can lead to inc reased concentrations of chromium in the serum, Determinations of the concentrations of metal in the serum and urine may be useful in the di agnosis of patients who are symptomatic after a total joint replacemen t as increased levels are indicative of at least one mode of mechanica l dysfunction (for example, fretting corrosion) of the device.