Mechanical properties of porous metal total hip prostheses

The forged condition is the strongest form of the Co-Cr-Mo and Ti-6Al-4V alloys used in orthopaedics. Both the Co-Cr-Mo alloy and the Ti-6Al-4V alloy lose strength when incorporated into porous implants. The strength loss in the Co-Cr-Mo alloy is a generalized condition and is largely a result of the microstructure of these cast and then gravity-sintered prostheses. The greatest fatigue strength achieved throughout these porous Co-Cr-Mo implants is that of the cast alloy. The strength loss in diffusion-bonded, porous titanium-alloyed implants is largely a result of notch sensitivity. This strength loss is not a generalized condition; it is localized on the implant to regions of porous coating attachment. In implant regions apart from the porous coatings, these titanium implants can have the strength of other wrought or forged titanium alloy implants. To achieve a functionally strong implant, porous implant design needs to account for these losses in material strength. Implant strength should be verified experimentally and communicated to the orthopaedic surgeon for assessment of implant adequacy for a particular patient. Patient weight, activity, and life expectancy are important elements in judging the adequacy of an implant's strength.