Abstract
Introduction
Anterior knee pain following total knee arthroplasty continues to be prevalent and may result from abnormal loading of the patellofemoral joint. The kinematics and biomechanics of the patellofemoral joint are complex, and trochlear design likely plays a principle role in affecting patellofemoral contact. As such, understanding the implications of trochlear design on patellofemoral contact remains important. The goal of the present study was to characterize trochlear wear of retrieved femoral components, which may help elucidate the details regarding patellofemoral kinematics and contact properties in relation to design features.
Materials and Methods
Retrieved femoral components featuring a single design (cobalt-chrome, posterior stabilized, cemented components with fixed bearing design) were included in the study. Components were selected based on similar time-in-vivo, age, and BMI. The trochlea of femoral components was consistently divided into six equal zones. Trochlear wear and surface damage in each zone were assessed using visual inspection under low-magnification light microscopy and light profilometry.
Results
Ten implants were selected and were used for the topographical analysis. The implants were selected based on time-in-vivo (33.6 months±18), BMI (40.4 kg/m2±13.2), patient age (67.9 years old±13.3) and gender (6 males, 4 females). Revision diagnosis across the implants were infection (n=6), instability (n=2), loosening (n=1), and fracture (n=1). All zones of the trochlea of retrieved femoral components showed evidence of wear on visual assessment, however, surface profilometry showed that the amount of wear in the retrieved components was not significantly different from a new, unused reference component (p>0.05). In fact, surface skeweness was higher in the new component (p=0.026). Modes of wear included scratches (100%), striations (65%), pitting (43%), and delamination (13%). Zone 1, which includes the raised lateral flange, tended to have more damage than the other zones, but this was statistically non-significant (p=0.634). No significant differences were found between the remaining trochlear zones with respect to wear based on visual assessment and light-microscopy (p=0.634) or surface profilometry (p=0.469). No significant differences were found with between proximal and distal wear (p>0.05) as well as medial and lateral trochlear wear (p>0.05).
Conclusions
Femoral components exhibit trochlear wear after in-vivo use. The amount of wear, however, is not substantially different from its new state and may represent early polishing. While the raised lateral flange zone trended towards greater wear than other zones, this was not statistically significant. Overall, with modern trochlear design, there was no evidence of asymmetric or abnormal loading of the trochlea. Longer term retrieval studies are required to assess patterns of femoral component wear and determine the clinical correlation of these findings.
