Efforts to reduce wear in total joint arthroplasty have traditionally been focused on improving implant design and polyethylene quality.

However, these improvements do not address the roughening of the cobalt chrome femoral component surface. This roughening is due to two phenomena: 1)Abrasive wear - occurs when a hard third-body gets between two surfaces. While this gouges the polyethylene, the more important factor is the femoral component scratch that results. 2)Oxidative wear - occurs as the passive surface film on metal is sheared off and reformed, with an associated release of metal ions.

The resulting increase in counterface roughness has been reported to be a significant factor in accelerating polyethylene wear. How often do femoral components become scratched clinically? Perhaps more often than you think.

Retrieval Study ^1,2

• Thirteen consecutive cobalt chrome femoral components and their corresponding polyethylene inserts from primary and revision total knee arthroplasty were obtained at revision surgery. All were retrieved for sepsis and were normal functioning TKAs before infection.
• All 13 inserts displayed scratching and burnishing and all femoral condyles showed evidence of scratching aligned with and, in some cases, oblique to the direction of articulation.

Laboratory Wear Tests ⁹.

• ... a single scratch 2µm deep (with 1µm adjacent peak height) on a metal surface can cause a dramatic increase in the wear rate of UHMWPE (polyethylene).