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The Contribution of Biomaterials to the Dawning of the Age of the Forgotten Hip

By Robert Poggie

Primary total hip arthroplasty (THA) has undergone 25 years of product development, thanks to contributions from a host of materials technologies. The result? A reliable, fully-functional, pain-free, lifetime hip replacement for most patients. Using today’s lexicon, this now-routine procedure has been succinctly termed the “forgotten hip.” 

As is common in all areas of human progress, the road to the forgotten hip has been paved with certain pitfalls. One example is Sir John Charnley’s discovery of high density polyethylene in the early 1960s as a suitable material for the acetabular bearing, after learning that PTFE (Teflon) was not the solution. The success of THA depends upon many factors including design, surgical technique, post-operative care and materials, with the latter arguably being the most influential in realization of the forgotten hip today and in the future, for most primary THA patients. 

Before we predict advancements, let’s review how we arrived at the current standard for THA. 

Evolution of Fixation

In the early 1990s, cementless primary hip arthroplasty was rapidly supplanting cemented arthroplasty with polymethyl methacrylate, or PMMA, as the majority means of fixation. This shift can be traced back to the 1980s with the introduction of new thermal spray and sintered coating technologies, ranging from “large” beaded coatings most notably promoted by Howmedica, “small” sintered beads marketed by DePuy, fiber metal from Zimmer, hydroxyapatite from Osteonics and plasma sprayed titanium from Biomet.

Subsequently, all companies were offering one or more solutions for cementless fixation by the mid-1990s. (See Exhibit 1.) These surface modifications all had one primary purpose: to provide fixation of femoral and acetabular components to bone. The generally accepted range for porosity of the porous coatings for bone ingrowth was between 250 to 750 micrometers, which still holds true today.

Read more in BONEZONE.