Background: With extensive use of posterior
stabilized total knee arthroplasty implants, it is increasingly
important to assess the mechanical performance of this design alternative.
The purpose of this study was to examine the wear patterns at the
femoral cam-tibial post interface in a series of posterior stabilized prostheses
retrieved at revision arthroplasty.
Methods: Qualitative and quantitative wear analysis
was performed over the surface of the stabilizing posts from twenty-three
retrieved total knee components that had been implanted for a mean
of 35.6 months (range, 2.3 to 107.2 months). The implants were designs
from four different manufacturers. Digital images of the anterior,
posterior, medial, and lateral surfaces of the tibial post were
made for quantitative analysis and determination of a post wear score.
Wear was characterized with a grading system that isolates adhesive,
abrasive, and fatigue wear, inferring a weighted score from an estimation of
generated polyethylene debris.
Results: Evidence of wear or damage was observed
on all twenty-three of the stabilizing posts, including those revised
because of infection. On the average, 39.9% (range, 18.5% to
60%) of the post surface demonstrated some form of deformation,
with adhesive wear, or burnishing, being the predominant wear mechanism.
Seven posts (30%) exhibited severe damage with gross loss
of polyethylene. The wear caused premature failure and early revision
of two components: one of these failures was related to isolated
post wear and the other, to severe post wear and subsequent fracture.
Overall, wear was primarily posterior, but wear over the anterior, medial,
and lateral surfaces was also notable.
Conclusions: The cam-post articulation in posterior
stabilized implants can be an additional source of polyethylene
wear debris. The variability in wear patterns observed among designs
may be due to differences in cam-post mechanics, post location,
and post geometry. The surgeon should be aware that the cam-post
interface is not an innocuous articulation, and manufacturers should
be motivated to produce implants that maintain the function of the
post while limiting wear and surface damage.