John Charnely Cemeted Stem Design

 https://hipandkneebook.com/new-blog/2017/3/13/tha-implants-history-of-tha

Charnley Stem 

    Composite Beam Design 

    Collar /flange and a rough surface finish

    

Composite Beam or Shape close design 

    - relies on friction to maintain position of stem within cement mantle 

    - rough surface finish ( > 2 Ra ) collar / flange intended to minimized micromotion at prosthesis cement       interface. 

How does this fail ? 

        Composite beam designs fail mechanism-

        Due to movement at prosthesis cement interface,

        Rough surface abrades cement mantle, once  micro-movement is established.

        Gap formation in turn leads to increased micro movement and circulation of wear debris.