Background: Patellofemoral complications are a common cause of
failure of total knee replacement. In this study, we examined eighty-five
patellar components that had been retrieved for a variety of reasons after a
mean of 71.9 months in vivo. The objective of this study was to identify
factors contributing to surface damage of patellar components in total knee
Methods: The retrieved patellar components were of three primary
designs: dome-shaped, sombrero-shaped, and pseudo-anatomic. Five zones on each
specimen were evaluated for five different types of damage (creep, pitting,
delamination, abrasion, and burnishing). The severity of the damage was
assigned a score of 0 to 4, with 0 indicating no damage and 4 indicating
extreme damage. The extent of the damage was also assigned a score of 0 to 4,
with 0 indicating 0% and 4 indicating 76% to 100%. An asymmetry ratio was
calculated for each damage pattern to evaluate the uniformity of the
distribution of the damage across each component.
Results: Eighty-six percent of the components had a damage score of
=4 (product of the extent and severity scores) for at least one damage
mechanism (creep for 38% of the components, pitting for 47%, delamination for
26%, abrasion for 49%, and burnishing for 76%). Components that had been in
situ for more than two years had significantly more severe creep,
delamination, and burnishing than components that had been in place for less
than two years. Metal-backed designs had more severe damage than
all-polyethylene components. Factors that reduced the occurrence and severity
of polyethylene damage were a congruent patellar design (a non-dome-shaped
component) and the use of an asymmetric femoral component.
Conclusions: Damage to the patellar component was a common finding,
particularly when the implant had been retrieved more than two years after
implantation. Moreover, delamination was frequently found on the patellar
components, as has been observed by others who examined retrieved tibial
inserts. The results of this study suggest that the use of congruent patellar
components may reduce damage.
Clinical Relevance: Understanding the causes of failure of patellar
components may be important for addressing an etiology of pain and dysfunction
following total knee arthroplasty.
Level of Evidence: Prognostic Level II. See Instructions
to Authors for a complete description of levels of evidence.